Anatomy and Physiology Notes

CHAPTER 1

Interest in the human body and how it functions probably developed when our ancestors began to think about the reasons why people became ill and died. All earlier cultures had someone designated as a healer who was responsible for finding plants and herbs that cured body disorders. This healer also was responsible for praying or invoking the assistance of past ancestors to help in the healing process.
As cultures developed and science began to evolve, interest in and knowledge about the human body advanced. Leonardo da Vinci, an Italian (1452-1519), was the first to correctly illustrate the human skeleton with all of its bones. The Flemish anatomist Andreas Vesalius (1514-1564) wrote a book on the human body, and the English anatomist William Harvey (1578-1657) discovered how blood circulates through the body. These are just a few of the many contributors who added to our understanding of the human body and how it functions. Anatomy is the study of the structure or morphology of the body and how the body parts are organized. | |

| Physiology is the study of the functions of body parts, what they do and how they do it. These two areas of the organization of the body are so closely associated that it is difficult to separate them. For example, our mouth has teeth to break down food mechanically, a tongue that tastes the food and manipulates it and salivary glands that produce saliva containing enzymes that break down complex carbohydrates into simple sugars, thus beginning the process of digestion. | | |

| Pathology is the study of the diseases of the body. |
We still do not know everything about how the human body functions. Research is still going on today to discover the mysteries of this complex unit we call ourselves.
To facilitate uniformity of terms, scientists have adopted four basic reference systems of bodily organization. These systems are directions, planes, cavities and structural units. When referring to terms of direction, planes and cavities, the human body is erect and facing forward. The arms are at the sides and the palms of the hand and feet are positioned toward the front. All descriptions of location or position assume the body to be in this posture. anatomy is the structure of the body, and physiology is the function.
The study of the structure, or morphology, of the body and how the body parts are organized is known as; anatomy
The study of the functions of body parts, what they do, and how they do it is known as: physiology
The study of diseases of the body is known as pathology

When an anatomist (one who studies the human body’s structures) is describing parts of the body, it is necessary to make reference to their positions in regard to the body as a whole. The following directional terms have been established to facilitate these references. Use the figure on the right as your guide as these terms are defined.
Superior means uppermost or above. Example: the head is superior to the neck, the thoracic cavity is superior to the abdominal cavity.
Inferior means lowermost or below. Example: the foot is inferior to the ankle, the ankle is inferior to the knee. Anterior means toward the front. Example: the mammary glands are on the anterior chest wall. The term ventral can also be used for anterior. Ventral means the belly side. | |

| Posterior means toward the back. Example: the vertebral column is posterior to the digestive tract, the esophagus is posterior to the trachea. |

The term dorsal can also be used for posterior. Dorsal means the back side.
Cephalad (SEF-ah-lad) or cranial means toward the head. It is synonymous with superior. Example: the thoracic cavity lies cephalad (or superior) to the abdominopelvic cavity.

Occasionally, caudal (KAWD-al) is synonymous with inferior. However, caudal specifically means toward the tail and, as we know, humans do not have tails.
Medial means nearest the midline of the body. Example: the nose is in a medial position on the face, the ulna is on the medial side of the forearm.

Lateral means toward the side or away from the midline of the body. Example: the ears are in a lateral position on the face, the radius is lateral to the ulna.
Proximal means nearest the point of attachment or origin. Example: the elbow is proximal to the wrist, the knee is proximal to the ankle.
Distal means away from the point of attachment or origin. Example: the wrist is distal to the elbow, the ankle is distal to the knee.
With respect to the body, superior and inferior are terms of direction
An alternate term for anterior is ventral
The upper structures are considered to be superior and lower structures are inferior.
An alternate term for dorsal is posterior
Cephalad or cranial means toward the head.
Nearest the origin is proximal
The opposite of the nearest point of attachment is distal
The term superior means uppermost or above.
The term posteriormeans toward the back.
The term inferior means lowermost or below.
At the dermatologist’s office, Jiang Mei is told that she has a mole on the anterior aspect of her leg, just distal to the knee. What part of her leg would that be? Correct Answer: On the front of her lower leg on her shin.

Occasionally, it is useful to describe the body as having imaginary flat geometric surfaces passing through it called planes (see on the right). These terms are most useful when describing dissections to look inside an organ or the body as a whole.
A midsagittal (mid-SAJ-ih-tal) plane vertically divides the body through the midline into two equal left and right portions or halves. This is also referred to as a median plane.

A sagittal plane is any plane parallel to the midsagittal or median plane vertically dividing the body into unequal right and left portions.

A horizontal or transverse plane is any plane dividing the body into superior and inferior portions.

A frontal or coronal plane is one that divides the anterior (or ventral) and posterior (or dorsal) portions of the body at right angles to the sagittal plane. When organs are sectioned to reveal internal structures, two other terms are often used. A cut through the long axis of an organ is called a longitudinal section, and a cut at right angles to the long axis is referred to as a transverse or cross section.
The plane parallel to the median is the sagittal plane.
Dividing the body into superior and inferior parts is the transverse plane.
Anterior and posterior portions are divided by the coronal plane.
The vertical plane that divides the body through the midline into two equal left and right halves is known as the: midsagittal plane
The plane that divides the body into superior and inferior portions is known as the: horizontal plane
The plane that divides the anterior and posterior portions of the body at right angles to the sagittal plane is known as the: frontal plane

The body has two major cavities: the dorsal cavity and the ventral cavity . Each of these is further subdivided into lesser cavities. The organs of any cavity are referred to as the viscera (VISS-er-ah). | The dorsal cavity contains organs of the nervous system that coordinate the body’s functions. It is divided into the: | | |

| cranial cavity, which contains the brain | spinal cavity, which contains the spinal cord. | The ventral cavity contains organs that are involved in maintaining homeostasis or a constant internal environment within small ranges of deviation and includes the: | | |

| thoracic cavity |

abdominopelvic cavity
The first subdivision of the ventral cavity is the thoracic (tho-RASS-ik) cavity. It is surrounded by the rib cage. The thoracic cavity contains the heart in a pericardial sac referred to as the pericardial cavity, and the two lungs each covered by the pleural membrane are referred to as the pleural cavities.

A space called the mediastinum (mee-dee-ass-TYE-NUM) is found between the two pleural cavities. It contains the heart, thymus gland, lymph and blood vessels, trachea, esophagus and nerves. The diaphragm muscle separates the thoracic cavity from the abdominopelvic cavity.

The abdominopelvic cavity is the second subdivision of the ventral cavity. It contains the kidneys, stomach, liver and gallbladder, small and large intestines, spleen, pancreas and the ovaries and uterus in women.

Two other terms are used when discussing the cavities of the body. The term parietal (pah-RYE-eh-tal) refers to the walls of a cavity. Example: the parietal peritoneum lines the abdominal wall. The term visceral refers to the covering on an organ. Example: the visceral peritoneum covers abdominal organs.
The two major cavities of the body are the dorsal and ventral.
Internal organs are the viscera of the body.
The dorsal cavity is divided into the spinal and the cranial cavities.
Between the pleural cavities is the mediastinum
The lining of the abdominal wall is the parietal peritoneum
The muscle that separates the thoracic cavity from the abdominopelvic cavity is the: diaphragm
The body cavity containing the organs of the nervous system is the: dorsal cavity
The body cavity containing the heart and the lungs is the thoracic cavity
Studying the X-rays, Dr. Sangetha states, “You can see the outline of the pericardial sac here.” What cavity of the body is this X-ray targeting? Thoracic

All living material is composed of cells, the smallest units of life. Cells are organized into tissues. Tissues are organized into organs, and organs are part of the major systems of the body.
The cell is the basic unit of biologic organization. The liquid part of a cell is called protoplasm (PRO-toh-plazm). This protoplasm is surrounded by a limiting membrane, the cell membrane, also called the plasma membrane, which selectively determines what may enter or exit the cell. This protoplasm is an aqueous (watery), colloidal (grouping of large molecules) solution of various proteins, lipids, carbohydrates and inorganic salts that are organized into cellular structures referred to as organelles. These organelles, such as the mitochondria, ribosomes and lysosomes, among others, are discussed in further detail in Chapter 3. | A cell performs all the activities necessary to maintain life, including metabolism, assimilation, digestion, excretion and reproduction. Different kinds of cells make up a tissue (muscle or bone). | | |

| Different types of tissues make up an organ (stomach or heart). Finally, organs are grouped into systems (digestive system or nervous system). Each system of the body serves some general function to maintain the body as a whole. All of the diverse tissues of the body can be placed into one of four categories: 1. epithelial (ep-ih-THEE-lee-al) 2. connective 3. muscle 4. nervous |

Epithelial tissue covers surfaces and protects (both the outer surface like the skin and inner surfaces of organs like the intestine), forms glands and lines cavities of the body. It is made up of one or more layers of cells with very little, if any, intercellular material.

Connective tissue binds together and supports other tissues and organs. In many instances it is highly specialized (blood, bone, lymphatic tissue). It is made up of different kinds of cells that produce various fibers (elastin and collagen) embedded in a matrix (substance) of nonliving intercellular material.

Muscle tissue is characterized by elongated cells (so long in fact they are often referred to as muscle fibers) that generate movement by shortening or contracting in a forcible manner. There are three types of muscle tissue. Skeletal or voluntary muscle pulls on bones and causes body movements. Smooth or involuntary muscle is found in the intestines where it pushes food along the digestive tract. It is also found in arteries and veins where it pushes blood forward. Cardiac muscle is found only in the heart. It is also involuntary and causes contractions of the heart; these contractions pump the blood through thousands of miles of blood vessels.

Finally, nervous tissue is composed of nerve cells forming a coordinating system of fibers connecting the numerous sensory (touch, sight) and motor (muscular) structures of the body.

Organs are composed of cells integrated into tissues serving a common function (skin, liver, stomach, heart, lungs).

A system is a group of organs and includes: 1. Integumentary System 2. Skeletal System 3. Muscular System 4. Nervous System 5. Endocrine System 6. Cardiovascular System 7. Lymphatic System 8. Respiratory System 9. Digestive System 10. Urinary System 11. Reproductive System

The integumentary system is made up of two layers: the epidermis and the dermis. It includes the skin, hair, nails, sebaceous glands and sweat glands. Its functions include insulation of the body, protection of the body from environmental hazards such as the ultraviolet radiation of the sun and certain chemicals and regulation of body temperature and water. It also has receptor sites to detect changes in temperature and pressure.

The skeletal system is composed of bones, cartilage and the membranous structures associated with bones. It protects the soft and vital parts of the body and provides support for body tissues. Its bones act as levers for movement. This system also manufactures blood cells in red bone marrow and stores fat in yellow bone marrow.

The muscular system consists of muscles, fasciae (fibrous connective tissues), tendon sheaths and bursae (fibrous sacs). Skeletal muscles pull on bones to allow movement; smooth muscle pushes food through the digestive tract and blood through the circulatory system; and cardiac muscle causes contraction of the heart.

The nervous system consists of the brain, spinal cord, cranial nerves, peripheral nerves and the sensory and motor structures of the body. Its functions include controlling, correlating and regulating the other systems of the body; interpreting stimuli from the outside world; and controlling the special senses of sight, hearing, taste and smell.

The endocrine system consists of the endocrine (ductless) glands. The master gland, or pituitary, controls the other glands-thyroid, adrenal glands, ovaries and testes. These glands produce hormones that chemically regulate the body’s functions. This system works with the nervous system through the hypothalamus of the brain, which controls the pituitary gland.

The cardiovascular, or blood circulatory, system consists of the heart, arteries, veins and capillaries. Its function is to pump and distribute blood, which carries oxygen, nutrients and wastes to and from the cells of the body.

The lymphatic, or immune, system is made up of the lymph nodes, the thymus gland, the spleen and the lymph vessels. Its function is to drain tissue spaces of excess interstitial fluids and absorb fats from the intestine and carry them to the blood. It also protects the body from disease by developing immunities and destroying most invading disease-causing microorganisms.

The respiratory system is composed of the nasal cavities, pharynx, larynx, trachea, bronchi and lungs. It brings oxygen to and eliminates carbon dioxide from the blood.

The digestive system includes the alimentary canal (mouth, esophagus, stomach, small and large intestines, rectum and anus) with its associated glands (salivary, liver and pancreas). Its function is to convert food into simpler substances that along with other nutrients can be absorbed by the cells of the body, and eliminate indigestible wastes.

The urinary system is made up of two kidneys, two ureters, the bladder and the urethra. Its functions include the chemical regulation of the blood, the formation and elimination of urine and the maintenance of homeostasis.

The reproductive system consists of the ovaries, uterine tubes, uterus and vagina in the female and the testes, vas deferens, seminal vesicles, prostate gland, penis and the urethra in the male. Its functions include maintenance of sexual characteristics and the perpetuation of our species.
Protoplasm is the liquid portion of a cell.
The four categories of body tissue are epithelial, connective, muscle and nervous
Cardiac muscle is found only in the heart.
The integumentary system is made up of the dermis and the epidermis
Three kinds of muscle tissue are smooth, cardiac and skeletal
The skeletal system is composed of bones, cartilage, and the membranous structures associated with bones.
The respiratory system is responsible for bringing oxygen to, and eliminating carbon dioxide gas from, the blood.
Tissue that binds together and supports other tissues and organs is known as connective tissue.
The urinary system is made up of two kidneys, two ureters, the bladder, and the urethra.
A system is a group of organs that perform a common function.
The reproductive system consists of the ovaries, uterine tubes, uterus, and vagina in the female.
The smallest units of all living material are: cells
A group of organs that serve a common function is known as a: system
The body system composed of bones, cartilage, and the membranous structures associated with bones is the: skeletal system
The ductless glands that produce hormones that function to chemically regulate the body's functions are part of which body system? endocrine system
The system composed of the nasal cavities, pharynx, larynx, trachea, bronchi, and lungs is the: respiratory system
The membrane surrounding the protoplasm of a cell is known as the: cell membrane
Mrs. McGilroy, a retired schoolteacher, complains to her friends that her ankles are always swollen, even in the morning. What body systems could be affected? Cardiovascular; lymphatic

Homeostasis (hom-ee-oh-STAY-sis) is the maintenance (within varying narrow limits) of the internal environment of the body. One of the first scientists to discuss the significance of homeostasis to the survival of an organism was French scientist Claude Bernard (1813-1878). Homeostasis is essential to survival; hence, many of the body’s systems are concerned with maintaining this internal environment. Some examples of homeostasis are blood sugar levels, body temperature, heart rate and the fluid environment of cells. When homeostasis is maintained, the body is healthy. This is the reason your doctor takes your temperature and blood pressure as part of a routine examination.

After ingesting a meal, which is predominately carbohydrates (salad, vegetables, bread and perhaps fruit), the blood glucose level increases dramatically due to the breakdown of the complex carbohydrates by the digestive system into sugars such as glucose. Cells take in the glucose they need carried by the blood, but so much glucose is in the blood that now the pancreas secretes insulin, which moves the excess blood glucose into the liver where it is stored as glycogen, or animal starch. Between meals, when the blood glucose level drops below normal, the pancreas secretes glucagon, which breaks down the glycogen into glucose and returns it to the blood circulatory system for distribution to body cells. Thus, the glucose level in the blood plasma remains at a nearly constant level so that it does not remain elevated after a meal, nor does it drop too low between meals.
Body temperature regulation is another important example of homeostasis. When we go out on a hot summer day and our body temperature rises above 98.6oF, the hypothalamus of the brain detects this change and sends signals to various organs so that we sweat (sweating is a cooling process). As water is excreted by the sweat glands onto the skin, it evaporates in the air (evaporation is a cooling mechanism).

In addition, our blood vessels dilate to bring the blood near the skin’s surface to dissipate body heat. When our body temperature falls below 98.6oF, such as when we go out on a cold winter day, the hypothalamus sends signals to muscles, causing us to shiver to raise our body temperature; it also causes our blood vessels to constrict to conserve body heat.

Our body must constantly monitor itself to correct any major deviations in homeostasis. It does this by using what is referred to as a negative feedback loop. Feedback responses that revise disturbances to our body’s condition are examples of negative feedback. A good example of a negative feedback loop is the relationship between your home thermostat and your furnace. You set the thermostat at a temperature of 72oF. When the temperature in your home drops below 72oF, the furnace turns on to raise the house temperature. When the temperature goes above 72oF, the thermostat causes the furnace to turn off.

Our organ systems help control the internal environment of the body and cells so that it remains fairly constant. Our digestive, urinary, circulatory and respiratory systems work together so that every cell receives the right amount of oxygen and nutrients, and so waste products are eliminated fairly quickly and do not accumulate to toxic levels. If homeostasis is not maintained, the body will experience disease and, eventually, death.
The balanced maintenance of the internal environment is homeostasis
The body is cooled by the action of sweat glands.\
CHAPTER 2

Because all of the structures of the body (cells, tissues and organs) are composed of chemicals, it is necessary to have a basic understanding of the science of chemistry. In addition, the body functions through chemical reactions. For example, in the digestive process, complex foods are broken down through chemical reactions into simpler substances such as sugars that can be absorbed and used by the body’s cells. Later these simple substances are converted into another kind of chemical fuel, adenosine triphosphate (ATP) (ah-DEN-oh-seen try-FOS-fate), which allows the body cells to do work and function.
This chapter introduces you to some basic principles of chemistry that will assist in your comprehension of human anatomy and physiology. To understand the human body, it is necessary to understand the chemical basis of life. We will look at the structure of the atom, how atoms interact with one another to form compounds and how those compounds form the building blocks of life. All nonliving and living things are made of matter. Matter is composed of elements, which are primary substances from which all other things are constructed. Elements cannot be broken down into simpler substances. There are 92 elements that occur naturally. Other elements have been created artificially in the laboratory.

Chemistry is the science that deals with the elements, their compounds, the chemical reactions that occur between elements and compounds and the molecular structure of all matter. Students of anatomy need to have some basic knowledge of this field of stud
In the digestive process, complex foods are broken down into simpler substances like sugars
Sugar is eventually converted into a kind of chemical fuel called adenosine triphosphate
All living and nonliving things are made of matter
There are 92 natural elements.
The science that studies the elements, their compounds, the chemical reactions that occur between elements and compounds, and the molecular structure of all matter is known as: chemistry

Atoms are the smallest particles of an element that maintain all the characteristics of that element and enter into chemical reactions. Each atom consists of a relatively heavy, compact central nucleus composed of protons and neutrons.

Lighter particles called electrons orbit the nucleus at some distance from its center. Electrons are practically weightless, and each one carries a negative electrical charge (-).
Atomic nuclei are composed of protons and neutrons, except for the hydrogen nucleus, which contains only one proton. Each proton and neutron has one unit of atomic weight and is about 1800 times heavier than an electron. Thus, an atom’s weight results almost entirely from its protons and neutrons. A proton carries a positive charge (+), whereas a neutron is neutral and has no charge.

Like charges repel-they push away from each other. Thus, when you brush your hair on a dry day, like electrical charges build up on the brush and your hair so your hair flies away from the brush. Unlike charges attract. The clinging of clothes taken out of a dryer is due to the attraction of unlike electrical charges.
The nucleus of an atom is composed of protons and neutrons
The smallest particles of an element that maintain all of the characteristics of that element and enter into chemical reactions are known as: atoms
An atom consists of a nucleus containing positively charged protons and: neutral neutrons
Each element has a distinctive number of protons. An element is a substance whose atoms all contain the same number of protons and the same number of electrons. Because the number of protons equals the number of electrons, an atom is electrically neutral. The theory that suggested that all matter consists of atoms was proposed in 1808 by John Dalton (1766-1844). He stated that atoms were responsible for the combinations of elements found in compounds. The atomic theory developed from his proposal.

The atomic theory proposed that: 1. All matter is made up of tiny particles called atoms. 2. All atoms of a given element are similar to one another but different from the atoms of other elements. 3. Atoms of two or more elements combine to form compounds. 4. A chemical reaction involves the rearrangement, separation or combination of atoms. 5. Atoms are never created or destroyed during a chemical reaction.
In the atoms of some elements, the number of neutrons varies. Carbon is the element found in all living matter. Life on earth is based on the carbon atom. In fact, a whole branch of chemistry called organic chemistry studies the nature of the carbon atom and its chemical reactions. Different atoms of carbon may have different numbers of neutrons.
Atoms of carbon may have one of three different atomic weights-12, 13 or 14-depending on the number of neutrons. These different kinds of atoms of the same element are called isotopes and are designated as C12, C13 and C14. Each of these isotopes contains six protons and six electrons, but C12 has six neutrons, C13 has seven neutrons and C14 has eight neutrons. C14 is mildly radioactive and is used to estimate the age of fossilized human remains.

A radioactive isotope of iodine is used to treat disorders of the thyroid gland. The atomic number is the number of protons or the number of electrons. By the late 1800s, scientists discovered similarities in the behavior of the known elements. It was a Russian chemist, Dimitri Mendeleev (1834-1907), who suggested that the elements could be arranged in groups that showed similar physical and chemical properties. From his work, we have the modern periodic table of the elements, which arranges the elements by increasing atomic number in such a way that similar properties repeat at periodic intervals.
In summary, protons and neutrons make up the nucleus of an atom. Electrons orbit the nucleus. It is impossible to know exactly where any given electron is located at any given moment, but the area where it is found can be referred to as the electron’s orbital. Orbitals are grouped together to form energy levels consisting of electrons. Levels can contain more than one electron. Thus, atoms are represented as a round nucleus (containing protons and neutrons) surrounded by concentric circles representing the energy levels. | Carbon has two electrons in the first level and four electrons in the second level. | | |

| Hydrogen has a single electron in its first level and no other levels. |

Oxygen has two electrons in the first level and six electrons in the second level.
The theory about matter and atoms was proposed by John Dalton
Life on earth is based on the carbon atom.
Different kinds of atoms of the same element are called isotopes.
Oxygen has two electrons in the first level and six in the second.

Atoms combine chemically with one another in one of two ways, that is, they form bonds. Chemical bonds are formed when the outermost electrons are transferred (gained or lost) or shared between atoms. When the atoms of two or more different elements combine in this way, a compound (such as water, H2O) is created. This symbol H2O also represents a molecule. A molecule or compound is the smallest combination or particle retaining all the properties of the compound itself.

One type of bond is called an ionic bond. This kind of bond is formed when one atom gains electrons while the other atom loses electrons from its outermost level or orbit.

Atoms that gain electrons become negatively charged, whereas those that lose electrons become positively charged, each having originally been electrically neutral. The new charged atoms are called ions. Negatively charged ions (Cl-, for example) are attracted to positively charged ions (Na+). The resulting force that binds these ions together is an ionic bond.

Referring to the figure, notice that the sodium atom has a completely filled innermost level with two electrons, a completely filled second level with eight electrons but only one electron in its third level. The chlorine atom has a completely filled innermost level with two electrons, a completely filled second level with eight electrons but only seven in its third level. Because eight electrons fill the outermost level in forming the ionic bond, sodium loses its one electron to the chlorine atom’s outermost level, thus filling chlorine’s outermost level with eight electrons.

The resulting compound, sodium chloride (Na+Cl-), is common table salt formed by an ionic bond, held together by the attraction of the opposite electric charges of the ions. When immersed in water, compounds held together by ionic bonds tend to separate or dissociate into their constituent ions because of the attraction of the water molecule (which we shall discuss later in this chapter). Many of the substances required by human cells exist in nature in ionic form. Some examples are the mineral salts such as sodium, chloride, potassium, calcium and phosphate.

A second type of bond found in many molecules is the covalent bond. In this type of bond, the atoms share electrons to fill their outermost levels. Molecules containing covalent bonds do not dissociate when immersed in water. Four of the most important elements found in cells form this type of bond. They are carbon (C), oxygen (O), hydrogen (H) and nitrogen (N). They constitute about 95% of the materials found in cells. All of the cell’s larger molecules, and many of its smaller ones, contain such bonds; for example, the formation of the covalent bond between two hydrogen atoms forms the compound hydrogen gas (H2).

Another type of bond is the hydrogen bond. Hydrogen bonds are very weak bonds and help hold water molecules together by forming a bridge between the negative oxygen atom of one water molecule and the positive hydrogen atoms of another water molecule. Hydrogen bonds also help bind various parts of one molecule into a three-dimensional shape such as a protein molecule like an enzyme.
Elements or molecules furnishing electrons during a reaction are called electron donors (e.g., sodium); those that gain electrons during the process are called electron acceptors (e.g., chlorine when salt is formed).

Some very special molecules will gain electrons only to lose them to some other molecule in a very short time; these are designated as electron carriers. These molecules are discussed in Chapter 4 and are very important in making the cellular energy molecule ATP.

Bonds contain energy, the ability to do work. This results from the interaction of the electrons and the nuclei of the bonded atoms. If we measure the amount of energy present between two atoms, we discover that the amount varies as the distance between the atoms changes. When atoms are close to one another, the paths of their electrons overlap. The natural repulsion of these negatively charged electrons tends to drive the two atoms apart. Thus, the amount of energy necessary to keep them together is quite high. This type of bond contains a high degree of energy. If we break these bonds, as in the breakdown of a glucose (C6H12O6) molecule inside a cell, electron carriers in the cell will use the energy of the released electrons to put together an ATP molecule.

ATP is the high-energy fuel molecule that the cell needs to function. This high-energy molecule that is used in the cell is called adenosine triphosphate. This molecule is constantly being created and broken down to release its energy to do the cell’s work. It is abbreviated as ATP. It is created by adding a phosphate to adenosine diphosphate. When it is broken down (ATP --> ADP + PO4) it releases the energy contained in the phosphate bond. We shall discuss this in further detail in Chapter 4.
When atoms combine chemically, they form bonds
A combination of two or more different elements is called a compound.
An ionic bond is formed when one atom gains electrons and another loses one.
Negatively charged ions are attracted to positively charged ions.
In covalent bonds, atoms share electrons.
A very weak bond is the hydrogen bond.
Molecules furnishing electrons are called donors
Molecules gaining electrons are called acceptors
Elements or molecules furnishing electrons during a reaction are called: electron donors
A bond in which one atom gains electrons while the other loses electrons is known as what type of bond? Ionic
The combination of the atoms of two or more elements is known as a(n): compound
A bond in which atoms share electrons is known as what type of bond? Covalent
There are 10 common substances found in living systems. They are: 1. water 2. carbon dioxide gas 3. molecular oxygen 4. ammonia 5. mineral salts 6. carbohydrates 7. lipids 8. proteins 9. nucleic acids 10. adenosine triphosphate
Water is the most abundant substance in living cells, approximately 60% to 80%; plasma, which is the liquid portion of blood, is 92% water. Water is a small, simple molecule composed of two hydrogen atoms covalently bonded to one oxygen atom.

Because the oxygen atom attracts electrons more strongly than do the hydrogen atoms, water molecules are polar with a partial positive charge by the hydrogen atoms and a partial negative charge by the oxygen atom. This unique feature of the water molecule determines why ionic bonded molecules dissociate in water. Negatively charged ions (e.g., chloride) are attracted to the positively charged hydrogen atoms, and positively charged ions (e.g., sodium) are attracted to the negatively charged oxygen atoms. Thus, the ionic bonded molecule salt dissociates in water.
Water has a number of roles in cells. It takes part in some reactions, such as photosynthesis in plant cells, which supplies our earth with molecular oxygen, and respiration in both plant and animal cells, which produces energy. Photosynthesis: | |

| 6CO2 + 12H2O --> C6H12O6 + 6O2 + 6H2O; | | |

| Respiration: | | |

| C6H12O6 + 6O --> 6CO2 + 6H2O + energy in the form of ATP. |

Digestion of food requires water to break down larger molecules. This is called hydrolysis. Water serves as a medium or solvent for other reactions, and water is referred to as the universal solvent. The chemistry of life is dominated by the chemistry of water. Chemical reactions occur in cells between individual atoms, ions or molecules, not between large aggregations of these particles. It is as these particles move about in the water that they come in contact with other particles and chemical reactions occur. In addition, water is a basis for the transport of materials such as hormones and enzymes in the plasma of blood.

Water also absorbs and releases high levels of heat before its temperature changes, thus helping control normal body temperature. Vigorous exercise liberates heat from contracting muscle cells. This excess heat is absorbed by the water in the cells and then released. Water is part of amniotic fluid and protects the developing fetus. It is also part of the cerebrospinal fluid and protects the brain and spinal cord by functioning as a shock absorber. Finally, water is the base for all body lubricants such as mucus in the digestive tract and synovial fluid in joints.

The small carbon dioxide molecule (CO2) contains one carbon atom covalently bonded to two oxygen atoms. It is produced as a waste product of cellular respiration and must be eliminated quickly from the body through expiration via the respiratory system and the cardiovascular system. It is also necessary for photosynthesis in plant cells to convert the radiant energy of the sun into usable chemical energy such as glucose for both plant and animal cells. It is also a source of the element carbon, found in all organic compounds of living systems. If carbon dioxide is allowed to accumulate within cells, it becomes toxic by forming carbonic acid as it reacts with water. Hence, we exhale it quickly from the lungs.

Molecular oxygen (O2), formed when two oxygen atoms are covalently bonded together, is required by all organisms that breathe air. It is necessary to convert chemical energy (food), such as the energy found in a glucose (C6H12O6) molecule, into another form of chemical energy ATP that can be used by cells to do work. Because O2 is a product of photosynthesis, it becomes obvious how dependent we animals are on plants for our survival. Without plants there would be no molecular oxygen in our atmosphere, and without O2 there would be no life on our planet as we know it. The level of O2 in our atmosphere is maintained at a nearly constant level (about 21% of the gas in the atmosphere is oxygen) by the many different kinds of plants found on our earth.

The ammonia molecule (NH3) comes from the decomposition of proteins via the digestive process and the conversion of amino acids in cellular respiration to ATP molecules. Note that an important element in ammonia is nitrogen. Nitrogen is an essential element in amino acids, which are the building blocks of proteins.

Because even a small amount of ammonia is injurious to cells, the human body must quickly dispose of this material. Through enzymes, the liver converts the toxic ammonia to a harmless substance called urea. Because urea is soluble in water, the blood then carries the urea to the kidneys to be filtered and eliminated from the body as urine. Because many plants are able to use NH3 or the products of bacterial action on NH3 as a nitrogen source for protein synthesis, ammonia is a common constituent of fertilizers.

Mineral salts are composed of small ions. They are essential for the survival and functioning of the body’s cells. They function in numerous ways as parts of enzymes or as portions of the cellular environment necessary for enzyme or protein action. Calcium (Ca++) is necessary for muscle contraction and nervous transmission as well as building strong bones. Phosphate (PO4-) is necessary to produce the high-energy molecule ATP. Chloride (Cl-) is necessary for nervous transmission. Sodium (Na+) and potassium (K+) are also necessary for muscle cell contraction and nervous transmission.

Carbohydrates (kar-boh-HIGH-draytz) are made up of the atoms of carbon, hydrogen and oxygen in a 1:2:1 ratio (e.g., glucose or C6H12O6). The smallest carbohydrates are the simple sugars that cannot be made to react with water to produce a simpler form. Sugars are generally chains of either five or six carbon atoms. Important five-carbon sugars are ribose and deoxyribose, which are parts of the RNA and DNA nucleic acid molecules. Important six-carbon sugars are glucose and fructose (the suffix ose denotes a sugar). Note the repetition of the H-C-OH unit in the molecule. This is typical of sugars.

Starch, glycogen (animal starch), cellulose (the material of plant cell walls that forms fiber in our diets), chitin (KYE-tin) (the exoskeleton of arthropods such as insects and lobsters), as well as many other complex carbohydrates, are formed by bonding together a number of glucose molecules. Besides glucose there are other six-carbon sugars. Combinations of these with glucose result in another series of sugars such as common table sugar or sucrose, a disaccharide.

Carbohydrates have two important functions: energy storage (sugars, starch, glycogen) and cell strengthening (cellulose of plant cell walls and chitin in the external skeleton of arthropod animals). Energy storage is the more common function of carbohydrates.

There are a number of different kinds of lipids. Lipids are substances that are insoluble in water. Fats, phospholipids, steroids and prostaglandins are examples of these different kinds of molecules. We will concentrate on fats, which are a major kind of lipid. Of the fats in the human body, 95% are triglycerides, now called triacylglycerols (try-ass-il-GLISS-er-allz). They consist of two types of building blocks: glycerol and fatty acids.
Glycerol is a simple molecule similar to a sugar except that it has only a three-carbon chain. Each carbon of the chain is bonded to a hydrogen and a hydroxyl (-OH) group as well as to the carbons of the chain. Fatty acids are composed of long chains of carbon atoms of different lengths. All the carbon atoms are bonded to hydrogen atoms except the carbon at one end of the chain. This carbon atom is bonded to the carboxyl (-COOH) group, which makes these molecules slightly acidic. Most naturally occurring fatty acids contain an even number of carbon atoms, 14 to 18.

Fatty acids are composed of long chains of carbon atoms of different lengths. All the carbon atoms are bonded to hydrogen atoms except the carbon at one end of the chain. This carbon atom is bonded to the carboxyl (-COOH) group, which makes these molecules slightly acidic. Most naturally occurring fatty acids contain an even number of carbon atoms, 14 to 18.
A fatty acid is saturated if it contains only single covalent bonds as those found in whole milk, butter, eggs, beef, pork and coconut and palm oils. Too much of these fatty acids contributes to cardiovascular disease. Saturated fats tend to be solids at room temperature. However, if the carbon chain has one or more double covalent bonds between the carbon atoms, it is an unsaturated fatty acid. These fatty acids are good for you and are found in sunflower, corn and fish oils.
Unsaturated fats tend to be liquids at room temperature. Fats have a number of major roles in the body. Like carbohydrates they contain stored chemical energy. Fat found under the skin acts as an insulator to prevent heat loss. Any animal that lives in the Arctic or Antarctic region (polar bears, seals, whales or penguins) has a thick layer of insulatory fat. The camel’s hump is a thick deposit of fat to protect its internal organs from excessive rises in temperature in the hot desert. Fat also protects organs as a surrounding layer such as the layer around our kidneys to protect them from severe jolts.

Proteins are composed of carbon, hydrogen, oxygen and nitrogen covalently bonded. Most proteins also contain some sulfur. The basic building blocks of proteins are the 20 amino acids. They vary in both the length of their carbon chain backbones and the atoms connected to that backbone. However, each amino acid has a carboxyl group (-COOH), an amine group (-NH2), a hydrogen atom, and the R group. The R group refers to the different types of atoms and length of the chain. Covalent bonds form between different amino acids to form proteins. These are referred to as peptide bonds.
Proteins function in a number of very important ways in the human body. Many are structural proteins. Proteins are part of a cell’s membranous structures: plasma membrane, nuclear membrane, endoplasmic reticulum and mitochondria. In addition, actin and myosin are structural proteins found in a muscle cell. We could not move, talk, digest or circulate blood without the proteins actin and myosin. Chemical reactions inside a cell allow a cell to function properly.
These chemical reactions would not occur in cells without the assistance of enzymes. Enzymes are protein catalysts, which increase the rate of a chemical reaction without being affected by the reaction. In addition, our immune system functions because antibodies, which are proteins of a high molecular weight, are formed to combat foreign proteins called antigens that enter the body. Some examples of foreign proteins are bacterial cell membranes, virus protein coats and bacterial flagella. Finally, proteins are also a source of energy that can be broken down and converted to ATP just like carbohydrates and fats.

Proteins are also discussed in terms of their structure: 1. primary structure 2. secondary structure 3. tertiary structure 4. quaternary structure

The primary structure of a protein is determined by its amino acid sequence. The secondary structure is determined by the hydrogen bonds between amino acids that cause the protein to coil into helices or pleated sheets. This shape is crucial to the functioning of proteins. If those hydrogen bonds are destroyed, the protein becomes nonfunctional. Hydrogen bonds can be broken by high temperatures or increased acidity, resulting in changes in pH.

The tertiary structure is a secondary folding caused by interactions within the peptide bonds and between sulfur atoms of different amino acids. Changes affecting this structure can also affect the function of the protein. Finally, the quaternary structure is determined by the spatial relationships between individual units.

Two very important nucleic acids are found in cells. Deoxyribonucleic acid (DNA) (dee-ock-see-rye-boh-noo-KLEE-ik) is the genetic material of cells located in the nucleus of the cell. It determines all of the functions and characteristics of the cell. Ribonucleic acid (RNA) (rye-boh-noo-KLEE-ik) is structurally related to DNA. Two important types of RNA are messenger RNA and transfer RNA, which are important molecules necessary for protein synthesis (discussed in Chapter 3).

The nucleic acids are very large molecules made of carbon, oxygen, hydrogen, nitrogen and phosphorous atoms. The basic structure of a nucleic acid is a chain of nucleotides. The DNA molecule is a double helical chain, and the RNA molecules are single chains of nucleotides. A nucleotide is a complex combination of a sugar (deoxyribose in DNA and ribose in RNA), a nitrogen base and a phosphate group bonded to the sugar. There are two categories of nitrogen bases, which consist of a complex ring structure of carbon and nitrogen atoms: 1. purines 2. pyrimidine

Purines consist of a fused double ring of nine atoms. The two purine nitrogen bases are adenine and guanine. Pyrimidines consist of a single ring of six atoms. The three pyrimidine nitrogen bases are thymine, cytosine and uracil. The DNA molecule has adenine, thymine, guanine and cytosine. The RNA molecule substitutes uracil for thymine and also has adenine, cytosine and guanine. In the DNA molecule, adenine joins thymine, whereas cytosine always joins guanine in forming the double helical chain. We will discuss this structure in detail in Chapter 4.
Adenosine triphosphate (ATP) is the high-energy molecule or fuel that runs the cell’s machinery. All the food we eat (which is a form of chemical energy) must be transformed into another form of chemical energy (ATP) that allows our cells to maintain, repair and reproduce themselves. The ATP molecule consists of a ribose sugar, the purine adenine, and three phosphate groups. The energy of the molecule is stored in the second and third phosphate groups.

The breakdown of the glucose molecule and other nutrients provides the energy to make ATP molecules (discussed in greater detail in Chapter 4). An ATP molecule is made by putting together an adenosine diphosphate (ADP) with a phosphate group (PO4): ADP +PO4 + energy --> ATP. The energy stored in the ATP molecule is then used to run the cell and to perform activities such as structural repair, reproduction, assimilation and transport of materials across cell membranes. This occurs when we break down an ATP molecule by releasing the energy in the phosphate bonds: ATP --> ADP +PO4 + energy (to do cell processes).
Cells contain approximately 60 to 80 % water
Digestion of food requires water to break down larger molecules.
Carbon dioxide contains one carbon atom and two oxygen atoms.
Ammonia comes from the decomposition of proteins.
The smallest carbohydrates are the simple sugars
Two five-carbon sugars are ribose and deoxyribose
Two six-carbon sugars are glucose and fructose
In the body, 95% of fats are triglycerides
Triglycerides are now called triacylglycerols
Triglycerides consist of the building blocks glycerol and fatty acids
Catalysts increase the rate of a chemical reaction without being affected by it.
The three pyrimidine nitrogen bases are cytosine, uracil and thymine
ATP is made by putting together ADP with a phosphate group.
The most abundant substance in living cells is water

The plasma membrane of cells is a selectively permeable membrane. This means that only selected materials are capable of getting into and out of cells. The chemical structure of the cell membrane is responsible for this quality. The cell membrane is composed of an outer and inner layer of protein with a double phospholipid layer in between. This chemical arrangement allows water to pass into and out of the cell with ease. However, water is not the only material needed for the cell’s survival. Cells need food like sugars, amino acids to make proteins and nutrients like the mineral salts. Materials pass through the cell’s membrane in three different ways: diffusion, osmosis, and active transport.

Diffusion is the movement of molecules through a medium from an area of high concentration of those molecules to an area of low concentration of those molecules. As an example of diffusion, think of a closed perfume bottle in a room. Within the stoppered bottle, perfume molecules are in constant motion; they are in the liquid and the gaseous state. Those in the gaseous state are in faster motion than those in the liquid state. In the air of the room, there are also molecules in motion such as water vapor, oxygen, nitrogen and carbon dioxide gas.
When the perfume bottle is opened, perfume molecules randomly move out of the bottle and randomly bump or collide with those other molecules in the air. The collisions are like bumping billiard balls on a pool table. The random collisions eventually bump the perfume molecules toward the walls of the room and eventually throughout the room. If the perfume bottle is opened at one end of the room and you are standing at the opposite end of the room, you would eventually smell the perfume once the molecules reached your end of the room. A person standing near the perfume bottle when it was opened would smell the perfume molecules before you did.

The random collisions of diffusing molecules are referred to as Brownian movement after Sir Robert Brown, an English scientist who described this kind of movement in 1827.

Despite the randomness of these collisions, over time there is a net displacement of perfume molecules from areas of high concentration (on and near the perfume bottle) to areas of low concentration (at the other end of the room). This is diffusion. Eventually, the proportion of perfume molecules being bumped back to the perfume bottle will equal the proportion of perfume molecules being bumped away from the bottle and the molecules will be evenly spread throughout the room.

Temperature has an effect on diffusion. The higher the temperature, the faster the movement. Think of a chunk of ice. Low temperature keeps the molecules moving very slowly, so the water is in a solid state. As temperature increases, molecular motion increases and the water moves to a liquid state. The ice melts. Continued heating, such as putting a pot of water on a stove, increases molecular motion even further so that the water becomes water vapor and moves into the gaseous state.

An example of an important diffusion in the human body is the uptake of oxygen by the blood in the lungs and the release of carbon dioxide gas to the lungs from the blood. Blood returning to the lungs is low in oxygen but high in carbon dioxide gas as a result of cellular respiration. When we breathe in air, we take in oxygen gas, so the lungs have lots of oxygen but little carbon dioxide gas.
The oxygen moves from an area of high concentration (the lungs) to an area of low concentration (the blood) by diffusion. Similarly, the carbon dioxide gas moves from an area of higher concentration (the blood) to an area of low concentration (the lungs) by diffusion. We exhale to get rid of the carbon dioxide gas now in the lungs

Osmosis (oz-MOH-sis) is a special kind of diffusion. Osmosis pertains only to the movement of water molecules through a selectively permeable membrane (e.g., a plasma membrane) from an area of high concentration of water molecules (e.g., pure water) to an area of low concentration of water molecules (e.g., water to which a solute such as salt or sugar has been added).

Osmosis can be demonstrated fairly simply by separating pure distilled water with a selectively permeable membrane (a barrier that will allow only water to pass through it but not solutes such as salt) and adding a 3% salt solution to the water on the other side of the membrane.

The water level on the solute side will rise, and the water on the pure water side will drop. The rise in water on the open-ended flask tube opposes atmosphere pressure and gravity and will eventually stop rising. At this equilibrium level, the number of water molecules entering the solute area equals the number of water molecules leaving the solute area. The amount of pressure required to stop osmosis is a measure of osmotic pressure. The solution stops rising when the weight of the column equals the osmotic pressure.

The mechanism of osmosis is simple. The salt in the column of water in solution cannot pass through the selectively permeable membrane. Salt is in higher concentration in the solution. Water is in lower concentration in the column because salt has been added to the water. However, the water in the beaker is pure distilled water; there are no solutes in it. The water, which can move through the selectively permeable membrane, causes the observed increased height of the water column in the flask. The water “tries” to equalize its concentration in both the beaker and the flask. Thus, the water moves from an area of high concentration in the beaker through the selectively permeable membrane.
Selectively Permeable Biologic Membranes |

Many biologic membranes are selectively permeable, such as the membranes of cells. The effects of osmosis on red blood cells can easily be demonstrated. If a red blood cell is placed in a normal saline solution (an isotonic solution) where the salt concentration outside the red blood cell equals the salt concentration inside the red blood cell, water molecules will pass into and out of the red blood cell at an equal rate, and there will be no observed change in the shape of the red blood cell.

If, however, the red blood cell is placed in pure distilled water (a hypotonic solution) where the water molecules are in a higher concentration outside the red blood cell, water will move into the red blood cell, causing it to swell and eventually rupture.

If the red blood cell is placed in a 5% salt solution (a hypertonic solution) where there is more water inside the red blood cell than in the solution, the red blood cell will lose water to the solution and will shrivel up or crenulate.

Because blood in the circulatory system is under pressure due to the beating of the heart, much blood plasma (the fluid part of blood, which is predominantly water with dissolved and colloidal suspended materials in it) is lost into surrounding tissues in the highly permeable one-cell-thick capillaries. Colloidally suspended proteins in the blood cannot pass through the capillary cell membranes; thus, they cause an osmotic pressure large enough to reabsorb most of the fluid that escapes from the capillaries.
Active Transport |

Although water and a few other substances with small molecular weights can osmose into the cells that need them, osmotic transportation is insufficient for most of the cell’s needs. Sugars, amino acids, larger proteins and fats are needed by the cell to produce ATP and to maintain and create structure. Cells obtain these nonosmotic or nondiffusable materials by a special mechanism called active transport. This mechanism, however, needs energy in the form of ATP to overcome the osmotic/diffusional barriers-another major reason that ATP is so important to a cell’s survival. Active transport is the transportation of materials against a concentration gradient or in opposition to other factors that would normally keep the material from entering the cell.
The movement through a medium from high concentration to low concentration is called diffusion
If the solutions inside a cell and outside a cell are the same, it is isotonic
The movement of fluid and solutions through a selectively permeable membrane from an area of high concentration to an area of low concentration is known as osmosis
The transportation of materials against a concentration gradient or in opposition to other factors that would normally keep the material from entering the cell is known as: active transport

pH is defined as the negative logarithm of the hydrogen ion concentration in a solution: pH 5-log [H+]. Pure water has a pH of 7. Remember that when distilled water (H2O) dissociates, for every H+ ion formed, an OH- ion is also formed. Or, in other words, the dissociation of water produces H+ and OH- in equal amounts. Therefore, a pH of 7 indicates neutrality on the pH scale. The figure shows the pH of various solutions.

If a substance dissociates and forms an excess of H+ ions when dissolved in water, it is referred to as an acid. All acidic solutions have pH values below 7. The stronger an acid is, the more H+ ions it produces and the lower its pH value. Because the pH scale is logarithmic, a pH change of 1 means a 10-fold change in the concentration of hydrogen ions. So lemon juice with a pH value of 2 is 100 times more acidic than tomato juice with a pH of 4.

A substance that combines with H+ ions when dissolved in water is called a base or alkali. By combining with H+ ions, a base therefore lowers the H+ ion concentration in that solution. Basic, also called alkaline, solutions have pH values above 7. Seawater with a pH of 8 is 10 times more basic than pure distilled water with a pH of 7. In our bodies, saliva in our mouths has a pH value slightly lower than 7 so it is just slightly acidic, whereas the stomach with its gastric juice and hydrochloric acid is very acidic with a pH value near 1. Our blood on the other hand has a pH value of 7.4, making it just slightly basic. Urine has a pH of 6, which, although acidic, is not as acidic as tomato juice with a pH of 4.

The pH inside most cells and in the fluid surrounding cells is fairly close to 7. Because enzymes are extremely sensitive to pH, even a small change can render them nonfunctional; thus, our bodies have buffers. A buffer is a substance that acts as a reservoir for hydrogen ions, donating them to a solution when their concentration falls, and taking the hydrogen ions from a solution when their concentration rises.

Buffers are necessary because the chemical reactions in cells constantly are producing acids and bases. Buffers help maintain homeostasis within cells in regard to pH levels. Most buffers consist of pairs of substances, one an acid and the other a base. For example, the key buffer in human blood is the acid-base pair bicarbonate (a base) and carbonic acid (an acid). Carbon dioxide and water combine chemically to form carbonic acid (H2CO3). The carbonic acid then can dissociate in water, freeing H+ ions and bicarbonate ions HCO3-. The blood’s pH can be stabilized by the equilibrium between these forward and reverse reactions that interconvert the H2CO3 carbonic acid and the HCO3- bicarbonate ion (base).
The negative logarithm of the hydrogen ion concentration in a solution is pH
A Buffer is a substance that acts as a reservoir for hydrogen ions.
A substance that dissociates and forms an excess of H+ ions when dissolved in water is referred to as an acid
While investigating life on another planet, an astronaut encounters an alien whose body has the same chemical composition as the human body. What would be the most abundant substance in the alien’s body? Water
If that alien removed all the sodium from the astronaut, what body systems would be affected? Muscular system; nervous system
Everett was watching children playing a game, tossing a ball back and forth between two groups. “Wow,” he said, “that’s just how a covalent bond works.”

CHAPTER 3
The cell is the basic unit of biologic organization. Our bodies are made up of trillions of cells. Although cells have different functions in the body, they all have certain common structural properties.
Cells are composed of a fluid medium called protoplasm surrounded by a cell or plasma membrane. Structures within this protoplasm are called organelles.
Protoplasm
| All cells are composed of protoplasm, which is an aqueous colloidal solution of carbohydrates, proteins, lipids, nucleic acids and inorganic salts surrounded by a limiting cell membrane. |
This protoplasm (proto meaning “first” and plasm meaning “formed”) is predominantly water with organic compounds, called organelles, in a colloidal suspension and inorganic compounds in solution.
Subdivisions of Protoplasm | When one observes a cell under the microscope in a laboratory, the most prominent structure in the cell is the nucleus, which is the control center of the cell. For this reason, the protoplasm of the cell is subdivided into two sections: 1. the protoplasm inside the nucleus is called nucleoplasm 2. the protoplasm outside the nucleus is called the cytoplasm |
Organelles are the building blocks of structures within the protoplasm. Some organelles are common to most cells. Higher cells like those of the human body are called eukaryotic cells (eu = true); cells that do not have membrane-bound organelles (e.g., bacteria) are called prokaryotic cells.
Organelles that are common to all eukaryotic cells are the: 1. nucleus 2. mitochondria 3. endoplasmic reticulum 4. ribosomes 5. Golgi apparatus 6. lysosomes 7. Specialized Organelles | If a cell has a specialized function that other cells do not have, for example, movement, the cell will have specialized organelles. Cells in our bodies that move materials across their exposed or free surface will be covered with row on row of hundreds of cilia. |
(For instance, cells in our respiratory tract produce mucus to trap dust and microorganisms that get past the hairs in our nose then move the material to our throat to be swallowed and passed out through the digestive system.) The human sperm cell, which must travel up the uterus of the female to the upper one-third of the fallopian or uterine tube to fertilize an egg, has a flagellum to propel it along its journey. Plant cells that do photosynthesis (the conversion of light energy into chemical energy, i.e., foods like sugars) have special organelles called chloroplasts.
Cells vary in size and most cells are too small to be seen with an unaided eye. Cells are measured in terms of microns (MY-kronz), more commonly called micrometers (my-KROM-ee-terz). One micrometer (µm) equals one-thousandth (10-3) of a millimeter. Most eukaryotic cells range in size from 10 to 100 micrometers in diameter (10 to 100 millionths of a meter).
Two German scientists laid the foundation of what we call today the cell theory. In 1838, Matthias Schleiden, a botanist, after careful study of plant tissues, stated that all plants are composed of individual units called cells. In 1839, Theodor Schwann, a zoologist, stated that all animals are also composed of individual units called cells. Thus the foundation of our modern cell theory was formed.
The modern cell theory consists of the following principles: 1. Cells are the smallest complete living things-they are the basic units of organization of all organisms. 2. All organisms are composed of one or more cells in which all life processes occur. 3. Cells arise only from preexisting cells through the process of cell division. 4. All of today’s existing cells are descendants of the first cells formed early in the evolutionary history of life on earth.
Living cells were observed a few years later by the Dutch naturalist Anton von Leeuvenhoek. He observed pond water under his microscope and was amazed at what he saw in what he believed was pure water. He called the tiny organisms in the water animalcules (meaning little animals). It took, however, almost another 150 years before the significance of cells as the building blocks of biologic organization was to take hold.
All cells are surrounded by a cell membrane. This membrane is often called the plasma membrane or the plasmalemma.
Under the high magnification of an electron microscope, a cell membrane is composed of a double phospholipid layer with proteins embedded in the phospholipid layer.
The phospholipids look like balloons with tails. The round balloon-like part is hydrophilic (attracts water) and the double tails are hydrophobic (repels water). This arrangement allows for the easy passage of water molecules through the cell membrane via osmosis (discussed in Chapter 2).
The proteins embedded in the double phospholipid layer of the cell membrane allow for the passage of molecules and ions across the cell membrane. They act as channels, active transport areas, receptor sites and identity markers for the cell.
Some proteins make transport channels for small dissolved ions, others act as enzymes for the active transport of materials into the cell against a concentration gradient and need adenosine triphosphate (ATP) to function, other proteins act as receptor sites for hormones to gain entrance into the cell and still other proteins act as cell identity markers. In addition, some proteins in the phospholipid layer act as cementing materials for cell adhesion on the outside of cells to hold cells together; others act as structural supports inside the cell attaching to cytoskeleton structures, which hold organelles in place in the cytoplasm.
Proteins also make up the structure of the sodium-potassium pump, a unique feature of certain cell membranes like muscle cell membranes and nerve cell membranes.
These molecules of proteins and phospholipids are currently referred to in their arrangement as a fluid mosaic pattern. The molecules are like the tiles of a mosaic but rather than being embedded in a solid cement-like material, they are embedded in a fluid and can move slightly to allow the passage of materials across the cell membrane and thus into the cytoplasm of the cell.
This basic molecular structure of the cell membrane is the same for all other membrane-bound organelles of the cell.
The cell membrane is called the plasmalemma
The liquid portion of a cell is called protoplasm. The protoplasm outside the nucleus is called cytoplasm; the protoplasm inside the nucleus is called nucleoplasm.
The main constituent of cytoplasm is water. This water, however, has many different kinds of chemical compounds distributed among the water molecules.
Some of these compounds are nucleic acids like transfer ribonucleic acid (RNA) and messsenger RNA, enzymes, hormones and various other chemicals involved in the functioning of the cell. Some of these compounds are in solution in the water, whereas others are in a colloidal suspension.
In both solutions and colloids, substances are uniformly distributed throughout the water medium. In a solution, however, individual atoms or ions are distributed throughout the medium. In a colloid, clumps of atoms rather than individual atoms are distributed throughout the medium.
The factor that determines whether a substance will go into solution or a colloidal suspension in water is the electronic interaction between the molecules of the substance and the molecules of water. Because the oxygen atom in H2O has a stronger attraction for the electrons in the H-O bond than the hydrogen atom (it shares the electrons unequally), the oxygen atom is slightly negative and the two hydrogen atoms are slightly positive.
POLAR. A molecule with such an unequal electron distribution of bonding electrons is said to be polar. Because of this polarity of the water molecule, other polar compounds, like ionically bonded compounds such as salt (sodium chloride) are readily soluble in water and go into solution. The polarity of the water molecules lessens the electrostatic forces holding ionically bonded molecules together so that they dissociate into individual ions and dissolve in the water.
NONPOLAR. Other compounds such as covalently bonded molecules are made up of atoms that have equal attraction for the bonding electrons that hold them together. Thus, the bonding electrons are not attracted to one atom of the bond more than the other. Compounds with such unpolarized bonds are called nonpolar and do not dissolve readily in water. The organic compounds with the C-H bonds are nonpolar and thus go into a colloidal suspension in the watery medium of the cytoplasm. Proteins, carbohydrates, fats and nucleic acids are colloidally suspended in the cytoplasm, whereas the mineral salts like sodium, potassium, calcium, chlorine and phosphorous are in solution.
Some cellular components, such as storage granules and fat droplets, are neither dissolved nor suspended in the cytoplasm. These compounds are products of cellular functions that have collected at certain specific sites within the cytoplasm. The cytoplasm will also contain structures called vacuoles. A vacuole is an area within the cytoplasm that is surrounded by a vacuolar membrane. This membrane has the same structure as the cell membrane. A vacuole is generally filled with a watery mixture but can also contain stored food (food vacuole) or waste products of the cell.
The nucleus is the most prominent structure in the cell. It is clearly visible with a light compound microscope. It is a fluid-containing structure that is separated from the cytoplasm by the nuclear membrane, sometimes referred to as the nuclear envelope. The nucleus is the control center of the cell. Cells whose nuclei have been removed lose their functions. Cells with a nucleus transplanted from a different cell take on the characteristics of the cell from which the nucleus was taken.
A unique feature of the nuclear membrane or envelope is that it is composed of two membranes. The inner membrane surrounds and contains the nucleoplasm and its materials. The outer membrane is continuous with the endoplasmic reticulum (ER), an organelle discussed later.
The structure of the nuclear membrane is the same fluid mosaic pattern as the cell or plasma membrane.
The electron microscope has revealed the presence of pores or openings in the double nuclear membrane. These pores have a very fine partition to hinder the free transport or leakage of materials of the nucleoplasm but which allow the passage of materials from the nucleoplasm, which must gain access to the cytoplasm. For example, when protein synthesis must take place, the code to make the protein is on the DNA in the nucleus but the protein is made at a ribosomal site in the cytoplasm. The code is copied from the DNA by a special molecule called messenger RNA (mRNA), which leaves the nucleus through a pore to go to the ribosome.
The fluid medium of the nucleus is called the nucleoplasm. It consists of a colloidal suspension of proteins; the nucleic acids DNA, deoxyribonucleic acid(DNA) (dee-ock-see-rye-boh-noo-KLEE-ik ASS-id), and RNA, ribonucleic acid (rye-boh-noo-KLEE-ik ASS-id); enzymes and other chemicals of the nucleus. Many chemical reactions occur in the nucleoplasm and are essential to cellular function and survival, including cellular reproduction.
When the cell is stained, fine dark threads appear in the nucleus. This material is called chromatin (KROH-mah-tin) and is the genetic material of the cell.
The cells of the human body contain 46 chromosomes (22 pairs of autosomes and one pair of sex chromosomes: one member of each pair comes from the father and one member from the mother). The egg cell and the sperm cell contain one-half that number, or 23 chromosomes. Chromosomes are made of DNA molecules and proteins.
When the DNA molecules duplicate during cell division, they shorten and thicken and become visible. We now call the DNA chromosomes. When the cell is not dividing, the DNA molecules are long and thin and visible only as chromatin. All of the above terms are used to describe the different levels of chromosomal organization. This is discussed in greater detail in Chapter 4. DNA controls many of the functions of the cell.
The nucleolus (noo-KLEE-oh-lus) is a spherical particle within the nucleoplasm that does not have a covering membrane around it. It is composed of primarily DNA, RNA and proteins. A cell may have more than one nucleolus. This structure is the site of ribosomal synthesis. It is involved in protein synthesis because it makes the ribosomes and ribosomes are the sites of protein synthesis.
A mitochondrion (singular) or mitochondria (my-toh-KON-dree-ah) (plural) are small oblong-shaped structures composed of two membranes. The outer membrane gives a mitochondrion its capsule shape; the inner membrane folds on itself to provide a surface on which the energy-releasing chemical reactions of the cell occur. When viewed under a light compound microscope, mitochondria appear only as small, dark granules in the cytoplasm. It is the electron microscope that has revealed to us the true nature of the mitochondria.
Cristae
| The folds of the inner membrane are called cristae (KRIS-tee). It is on the cristae that cellular respiration occurs, where food (chemical energy) is converted into another usable form of chemical energy, ATP. For this reason, the mitochondria are known as the powerhouses of the cell. |

| In its most simple expression, cellular respiration can be stated as follows: |

| Food (like glucose) + oxygen --> energy + waste. |

| C6H12O6 + 6O2 --›ATP + 6CO2 + 6H2O. |

|
Most of the energy-producing reactions, which occur in the mitochondria, take place on the surface of the cristae. Cells with high energy requirements (like muscle cells) will have mitochondria with many folds or cristae. Cells with low energy requirements, like the lining of the cheek (epithelial cells), will have mitochondria with fewer folds or cristae. All cells will have approximately the same number of mitochondria. They are inherited from the mother via the egg cell. Mitochondria also contain mitochondrial DNA.
Lysosomes (LIGH-so-sohmz) are small bodies in the cytoplasm that contain powerful digestive enzymes to enhance the breakdown of cellular components. The structure and size of lysosomes vary but they are generally spherical. They have three general functions: 1. Digest stored food 2. Maintenance and repair of cellular components 3. Suicide agents

They act in conjunction with stored food vacuoles. When a cell needs more energy, a lysosome will fuse with a stored food vacuole to break down the stored food into a more usable form that can go to a mitochondrion to be converted into ATP. For example, starch, a complex carbohydrate, will be broken down into simple sugars, protein into amino acids and fats into fatty acids and glycerol.
Lysosomes also act in the maintenance and repair of cellular components. If a section of ER needs to be rebuilt, the lysosome will break down the membrane into amino acids, fatty acids, glycerol and so on and material that can be recycled to build new protein and phospholipids.
Lysosomes also act as suicide agents in old and weakened cells. This process is known as autolysis (aw-TAHL-ih-sis). The lysosome will expel all of its enzymes directly into the cytoplasm of the cell to destroy the cell and its organelles.
The endoplasmic reticulum (en-doh-PLAZ-mik re-TIK-you-lum), or ER, is a complex system of membranes that forms a collection of membrane-bound cavities. These often interconnect into a membrane-bound system of channels within the cytoplasm. The shape and size of these cavities vary with the type of cell. When the cavities are sac-like or channel-like, they are called cisternae (sis-TER-nee) and are used to store and transport materials made by the cell. The ER is attached to the outer membrane of the nuclear membrane or envelope and ultimately connects with the cell membrane. With the use of the electron microscope, it was discovered that there are two types of ER: 1. a rough ER 2. a smooth ER

All cells will have a rough or granular ER. It is called rough or granular because it has ribosomes attached to it. These are the granules on the ER. Because of the attached ribosomes, the rough ER is a site of protein synthesis. Proteins that will be secreted by the cell are synthesized there. The cavities and vesicles of the rough ER serve in the segregation and transport of these proteins in preparation for further discharge and processing. The rough ER may also be involved in the collection of digestive enzymes to form lysosomes.
Occasionally, a smooth or agranular ER will be attached to a granular ER. Structurally, the agranular form differs from the rough form. It does not have attached ribosomes. It also differs in function. Only certain cells have the agranular or smooth ER. It is found in the cells of the gonads in which sex hormones are being synthesized. One function appears to be sex hormone synthesis. It is also found in the cells of the lacteals of the villi of the small intestine. Thus, it is also believed to be involved in the transportation of fats.
The Golgi (GOHL-jee) apparatus is also called the Golgi body. It consists of an assembly of flat sac-like cisternae that resembles a stack of saucers or pancakes. Golgi bodies can differ in both size and compactness. They function as the points within the cell where compounds to be secreted by the cell are collected and concentrated. They may be seen attached to the ER. When the cell’s secretions are a combination of both proteins and carbohydrates, the carbohydrates will be synthesized in the Golgi apparatus and the complexes of carbohydrates and proteins are assembled there. In the pancreas, enzymes synthesized by the ribosomes are collected in the membranes of the Golgi apparatus and then are secreted. Lysosomes may also form at the Golgi body when digestive enzymes are collected there.
Ribosomes (RYE-boh-sohmz) are tiny granules distributed throughout the cytoplasm and are attached to the rough or granular ER. They are not surrounded by a membrane. Ribosomes are composed of ribosomal RNA and proteins. Messenger RNA attaches to ribosomes during protein synthesis. There are many, many ribosomes in the cell because they are so essential to cell function. They are the sites of protein synthesis.
Proteins are essential to cellular function and structure. Proteins are part of membrane structures (proteins are embedded in the double phospholipid layer). Enzymes are protein catalysts (all chemical reactions in the cell require enzymes), and our immune system functions through the production of antibodies (large proteins) that attack foreign proteins (antigens).
The code to make a particular protein lies on a DNA molecule in the nucleus. Genes on the DNA molecule constitute the code. However, proteins are made at the ribosomes. Therefore, this code must be copied and taken to the ribosomes.
A special molecule called messenger RNA (mRNA) copies the code from the DNA molecule in the nucleus. This process is called transcription and occurs with the assistance of an enzyme called RNA polymerase. The mRNA then leaves the nucleus through a nuclear pore and goes into the cytoplasm to a ribosome or group of ribosomes. The ribosome will now assist in the assemblage of the protein because it now has the code or recipe to produce the protein. To make the protein, the ribosome now needs the ingredients, which are amino acids. In a cell, proteins are assembled from amino acids.
Another molecule will now go into the cytoplasm and collect the amino acids. This molecule is transfer RNA (tRNA). It is coded for a particular amino acid by means of three nitrogen bases at one end of the molecule known as the anti-codon. These three bases will fit or match with three bases on the mRNA molecule called the codon. In this way, a series of tRNA molecules bring amino acids to certain sites on the mRNA molecule. This process is called translation (reading the code and bringing the appropriate amino acids in sequence along the mRNA).
Now the ribosomes, with the assistance of enzymes, put the amino acids together by linking them up and forming a polypeptide chain. The numerous ribosomes found in the cell indicate the importance and significance of protein synthesis to the survival and function of the cell.
Two centrioles (SEN-tree-olz) are found only in animal cells at right angles to each other near the nuclear membrane. The pair together is referred to as a centrosome (SEN-troh-sohm). They are composed of nine sets of triplet fibers. The inner fiber of each triplet is connected to the outer fiber of the adjacent triplet by a subfiber.
During cell division, the centrioles move to each side of the dividing cell and position themselves at a location called the opposite pole of the cell. They now form a system of microtubules, which are long, hollow cylinders made of a protein called tubulin. These fibers or microtubules redistribute the duplicated chromosomes during cell division into the appropriate new daughter cells.
Cristae

The folds of the inner membrane are called cristae (KRIS-tee). It is on the cristae that cellular respiration occurs, where food (chemical energy) is converted into another usable form of chemical energy, ATP.

Cilia (SIL-lee-ah) and flagella (fla-JELL-ah) are cellular organelles located on the cell surface. They are composed of fibrils that protrude from the cell and beat or vibrate. Some single-celled organisms use these structures to move through a medium.
For example, Euglena has a flagellum that propels it through the water, whereas a Paramecium is covered with row upon row of hundreds of cilia to allow it to swim in pond water. In the human body the male sperm cell is propelled by a single beating flagellum that assists it in reaching the female egg in the upper part of the fallopian or uterine tube where they unite in fertilization. Stationary cells, like those that line our respiratory tract, are covered with cilia on their free edge to move the mucus-dust package upward across the cell surfaces to bring this material to the throat to be swallowed and then discharged from the body.

Although cilia and flagella are similar anatomically, a flagellum is considerably longer than a cilium. A cell with cilia will have row on row of cilia, but a cell with flagella will have one (like the sperm cell) or two or four like some single-celled protozoans.
Externally, these structures are hairlike protrusions from the cell membrane. Internally, they are composed of nine double fibrils arranged in a cylindrical ring around two single, central fibrils. The microtubules or fibrils of the flagellum arise from a structure called the basal body found just below the area from which the flagellum protrudes from the surface of the cell membrane. The basal body or plate has a cylindrical structure like the centriole, that is, it is also composed of nine sets of triplet fibers.
In our laboratory exercise on cells, we will examine and compare plant cells with animal cells. Therefore, it is necessary to discuss these organelles found only in plant cells. There are three plastids found in plant cells. The most common and most numerous of these are the chloroplasts (KLOR-oh-plastz) that cause plants to look green.
Chloroplasts
| Chloroplasts are large organelles found mainly in plant cells. They contain the green pigment chlorophyll. These organelles are the site of photosynthesis. It is here that the light energy of the sun is converted into chemical energy and food for use by both plants and animals. Without plants and their chloroplasts, animals could not survive on this planet. The process of photosynthesis occurs inside the chloroplast. This chemical equation is: |

| 6CO2 +12H2O-›C6H12O6 or glucose (sugar, food) + 6O2 (the air we breathe) + 6H2O |
Chloroplasts are large enough to be easily seen with a light microscope. They are enclosed by a membrane but the internal membranous structure is complex. The inside contains many stacks of membranes called a granum. A granum is made of a stack of individual double membranes called a thylakoid (THIGH-lah-koid). The grana (plural) are connected to one another by a different system of membranes called lamella. The grana are made of proteins, enzymes, chlorophyll and other pigments arranged in a layered structure.
Plant cells also have two other types of plastids. Chromoplasts (KROH-moh-plastz) are similar in structure to chloroplasts but they contain other pigments like the carotenoid pigments. The carotenoid pigments are xanthophyll (ZAN-tho-fill), which produces a yellow color (the skin on a banana), and carotene (KAR-oh-teen), which produces a red-orange color (tomatoes and carrots). These pigments also produce the colors of flower petals and fruits. Another type of plastid is the leucoplast (LOO-koh-plast). Leucoplasts do not have any pigments-they are storage plastids. An onion bulb is full of leucoplasts where sugar is stored and a potato contains leucoplasts where starch is stored.
The cell membrane of plant cells is surrounded by a semirigid covering called the cell wall made of a complex carbohydrate called cellulose (SELL-you-lohs). Cellulose is synthesized by Golgi bodies by linking up glucose units. Animal cells do not have cell walls. This material is what we call fiber in our diet. It cannot be digested, thus, it keeps our stools soft. We eat fruits and vegetables to maintain a balance of fiber in our diet. This fiber may help prevent the development of colon cancer.
CHAPTER 4
For cells to maintain their structure and function, chemical reactions must occur inside the cell. These chemical reactions require an input of biologically usable energy. The most common and available form of energy within a cell is the chemical energy found within the structure of an ATP (adenosine triphosphate) molecule. We use the term metabolism (meh-TAB-oh-lizm) to describe the total chemical changes that occur inside a cell. There are two subcategories of metabolism: | |

| anabolism (an-AB-oh-lizm) is an energy-requiring process that builds larger molecules from combining smaller molecules | | |

| catabolism (ka-TAB-oh-lizm), which is an energy-releasing process that breaks down large molecules into smaller ones. These cellular metabolic processes are often called cellular respiration or cellular metabolism. | | |

| These cellular metabolic processes are often called cellular respiration or cellular metabolism. |
Molecules of ATP are made within the cell during a stepwise decomposition (catabolism) of organic molecules (carbohydrates, fats and proteins). We measure the energy contained in food as calories. This decomposition releases the chemical energy (calories) stored in these organic foodstuffs and this energy is used to synthesize ATP (another form of chemical energy) from ADP (adenosine diphosphate) and PO4 (inorganic phosphate). Thus, ATP is the energy source available to the cell to be used for all cell processes: chemical reactions use ATP as an energy source to maintain cellular structure and function.

Photosynthesis by plant cells is the ultimate source of the organic molecules (foodstuffs) that will be decomposed to form ATP. Photosynthesis requires 6CO2 +12H2O in the presence of light and chlorophyll to produce C6H12O6 (glucose) an organic molecule + 6O2 (oxygen) as a waste product + 6H2O (water) as a waste product. The formation of ATP is the final step in the transformation of light energy into the chemical energy of a biologically usable form. This explains the significance of our dependence on plants to convert sun or light energy into food or chemical energy.
Cellular Metabolism | The most efficient cellular process by which ATP is formed during the breakdown of organic molecules requires molecular oxygen (O2). This process is called cellular or biochemical respiration or cellular metabolism. The overall chemical equation is: C6H12O6 + 6O2+6CO2 + 6H2O + energy in the form of ATP. | | |

| Respiration, therefore, requires an exchange of gases between the cell and its surroundings to allow the inflow of O2 to the cell and the outflow of CO2. Biochemical respiration is strictly the oxygen-requiring or aerobic process of ATP production. This biochemical meaning of respiration should not be confused with the everyday meaning of breathing. The most common substance decomposed aerobically in cells to produce ATP is glucose, C6H12O6. |

Introducing 3 Steps of Cellular Metabolism | The breakdown of a glucose molecule into carbon dioxide gas and water is a continuous process. However, we will discuss this process in three steps. The first step is called glycolysis (gligh-KOL-ih-sis). Because it does not require oxygen, it is also occasionally called anaerobic (without oxygen) respiration. This step occurs in the cytoplasm of the cell. The next two steps are called the Krebs citric acid cycle and the electron transfer or transport system. These two steps require oxygen and they occur in the matrix and on the folds or cristae of the mitochondria of the cell. |
To maintain structure and function, chemical reactions must occur in cells.
Total chemical changes occurring inside a cell are called metabolism.
The process using CO2, H2O, light and chlorophyll to produce food is called photosynthesis.
The energy-requiring process that builds larger molecules by combining smaller molecules is known as: anabolism
The energy-releasing process that breaks down large molecules into smaller ones is known as: catabolism
The first step in the biochemical respiration process is the breakdown of glucose, which is called: glycolysis

The first step in the biochemical respiration process is glycolysis. It is common to the aerobic breakdown of glucose and to the two different types of anaerobic breakdown of glucose molecules. One type of anaerobic glucose decomposition occurs in yeast cells (a type of fungus) and is called fermentation. The other type occurs in our muscle cells when we exercise and experience muscle fatigue and cannot get enough oxygen to our muscle cells. In the overall process of glycolysis, the C6 (backbone chain of six carbon atoms) sugar glucose is slowly broken down by various enzymatic steps to two C3 units of pyruvic (pye-ROO-vik) acid. Refer to the figure on the right as we discuss glycolysis.
The first step in glycolysis (which takes place in the cytoplasm) is the addition of a phosphate to the glucose. This process is called phosphorylation (fos-for-ih-LAY-shun). The phosphate comes from the breakdown of an ATP molecule into ADP and PO4, releasing the energy required to add the phosphate to the glucose. The glucose phosphate quickly changes to another C6 sugar phosphate called fructose phosphate. In another ATP requiring reaction, the fructose phosphate is phosphorylated by breaking down another ATP into ADP and PO4. This phosphate is added to the fructose phosphate, creating fructose diphosphate. So far we have not made any ATP but rather we have used up two ATP and these must be paid back from our final ATP production at the end of glycolysis.

In the next step of glycolysis, the fructose diphosphate splits or cleaves into two C3 molecules of phosphoglyceraldehyde (fos-foh-GLISS-er-AL-deh-hyde), abbreviated as PGAL. The PGAL is now oxidized (loses electrons) by the removal of two electrons and two H+ ions to form two phosphoglyceric (fos-foh-GLISS-er-ik) acids, abbreviated as PGA. The two hydrogen atoms that come off each of the two PGALs go to the electron transport system and are taken up by the electron carrier molecule nicotinamide adenine dinucleotide (nik-oh-TIN-ah-mide ADD-eh-neen dye-noo-klee-oh-tide) abbreviated as NAD. This step is actually part of the electron transport system and will result in the production of six ATP molecules. However, this step occurs only if oxygen is present. In this process, NAD gets reduced (gains electrons) to NADH2. Because there were two PGALs, it happens twice. Each time an NAD gets reduced to NADH2 and the electron transport system functions, three ATP molecules are made. Again, because it happened twice, a total of six ATP are made in this aerobic step.
Next, the two PGAs get broken down through a series of high-energy releasing enzymatic steps to two C3 molecules of pyruvic acid. So much energy is given off in these steps that four ADP and four PO4 get added to form four ATP molecules. The energy in the PGA molecules is converted to the high-energy four ATP molecules. In this step, we make four ATP but it is from these ATP that we must pay back the two ATP used in the beginning of glycolysis. Therefore, our net gain of ATP is only two ATP.
In summary, the glycolytic breakdown of one molecule of glucose produces two pyruvic acid molecules. It took two ATP to start the sequence and four ATP were produced. However, to pay back the two ATP, our net gain is only two ATP. However, we also produced two NADH2, which are part of the electron transport system. When oxygen is present, we produce six more ATP via electron transport. Aerobic glycolysis produces six plus two or eight ATP molecules. Anaerobic glycolysis produces only two ATP.
In the presence of O2, the two pyruvic acid molecules formed as a result of glycolysis are further broken down in the second step of biochemical respiration. This step is named after its discoverer, a German-born British biochemist, Sir Hans Krebs, who first postulated the scheme in 1937. This is the Krebs citric acid cycle (which takes place in the mitochondria). We will explain this cycle using only one of the two pyruvic acid molecules produced in glycolysis. When finished, we will multiply all products by 2.
The C3 pyruvic acid is first converted to acetic acid (ah-SEE-tic ASS-id) in a transition stage and then to the C2acetyl-CoA (ah-SEE-tal) by an enzyme called Co enzyme A. This causes the pyruvic acid molecule to lose a carbon and two oxygens in the form of CO2 gas as a waste product. It also loses two hydrogens to NAD, producing NADH2 (thus, via electron transport three ATP molecules are made in this step). The acetyl-CoA now enters the Krebs citric acid cycle. This occurs on the cristae of the mitochondria.
The C2 acetyl-CoA reacts with a C4 molecule oxaloacetic (ok-sah-low-ah-SEE-tik) acid to form the C6 molecule citric acid, hence the name of the cycle. No ATP is produced in this step but an important event occurs. CoA enzyme is regenerated to react with another acetic acid to continue the cycle. Another enzyme now converts the citric acid to the C5alpha-ketoglutaric(AL-fah KEY-toh gluh-TAYR-ik) acid. This causes the citric acid to lose a carbon and two oxygens as CO2 gas (waste product) and two hydrogens to NAD. Thus, NAD gets reduced via electron transport to NADH2 and three ATP are made. The C5 alpha-ketoglutaric acid now gets broken down into the first C4 molecule succinic (suk-SIN-ik) acid. It loses a carbon and two oxygens as CO2 gas (waste product) and two hydrogens twice to NAD. Thus, via electron transport six more ATP molecules are made. Succinic acid changes to another C4 molecule, malic (MAH-lik) acid. | |

| Finally, the malic acid loses two hydrogens to flavin adenine dinucleotide (FLAY-vin ADD-eh-neen dye-NOO-klee-oh-tide), abbreviated as FAD. This is another electron carrier of the electron transport system and two more ATP molecules are made in this step. The malic acid now is converted to the oxaloacetic acid. Also going from alpha-ketoglutaric acid to oxaloacetic acid another ATP equivalent is made. This molecule is actually guanosine triphosphate (GTP).In summary, for every pyruvic acid that enters the Krebs citric acid cycle, three CO2, four NADH2, one FADH2 and one ATP (GTP) are produced. Because two pyruvic acids entered the cycle, we must multiply all of these products by 2.The Electron Transport (Transfer) SystemMost of the ATP produced during biochemical respiration is produced in the electron transport system. Two NADH2 were produced in glycolysis. Two NADH2 were produced during the acetyl-CoA formation. Then six NADH2 and two FADH2 were produced in the citric acid cycle. The NAD and FAD all donate the electrons of the hydrogen atoms that they captured in these reactions to the enzyme systems on the cristae of the mitochondria. Each of these electron carriers has a slightly different electron potential. As the electrons from the cofactor NADH2 get transferred from one electron carrier to the next, they slowly give up their energy. This energy is used in the energy-requiring synthesis of ATP from ADP and inorganic phosphate.The electron transport system functions as a series of reduction/oxidation reactions. When NAD accepts the two hydrogens, it gets reduced to NADH2. When it gives up the two hydrogens to FAD, NAD gets oxidized while FAD becomes FADH2 and gets reduced. This series of redox reactions continues until the electrons of the hydrogen atoms get ultimately donated to oxygen. Several kinds of electron carriers participate in this process: the cofactor NAD, the cofactor FAD, quinone and the cytochrome system. There is some debate as to whether the hydrogen protons (2H+) are transferred along with the electrons (2e-) in this transport or not. This scheme illustrates why the breakdown of glucose requires oxygen (O2). Oxygen is the ultimate electron acceptor for the electrons captured by the cofactors during glucose decomposition. One ATP is formed during the first step of electron transfer from NADH2 to FAD. During the following transfer from FADH2 to quinone H2 to the cytochrome system to O2 (or ½ O2 =O), two more units of ATP are formed. You will notice that the cytochrome system only accepts the two electrons and then transfers them to oxygen (O). Therefore, quinone H2 must directly transfer the two hydrogen protons (2H+) to oxygen (O), thus producing the waste product water (H2O).As we examine the electron transport system, we observe that when electrons are donated to NAD, three ATP units are formed during the entire electron transfer. However, when the electrons are donated directly to FAD and NAD is bypassed, only two ATP units are formed during the electron transfer.Summary of ATP Production During Glycolysis The net products from glycolysis are two ATP units and two NADH2 per glucose molecule. Because each NADH2 molecule produces three ATP during electron transport, a total of eight ATP units result in glycolysis, which includes electron transport.Summary of ATP Production During the Citric Acid Cycle and Electron Transport In the Krebs citric acid cycle and transition stage, four NADH2, one FADH2 and one ATP (or GTP) are formed during the breakdown of each pyruvic acid. However, because each glucose molecule produces two pyruvic acid molecules, we actually form eight NADH2, two FADH2 and two ATP (or GTP) units. The number of ATP units formed during the citric acid cycle and electron transport then is 24 +4 + 2 + or 30 ATP or 24 + 4 = 28 ATP and 2 GTP. | In total, 30 ATP from the citric acid cycle and electron transport plus 8 ATP from glycolysis and electron transport produced a net gain of 38 ATP units per each glucose molecule or 36 ATP and 2 GTP. This represents a cellular capture of about 60% of the energy available from the breakdown of a single glucose molecule. This is very high efficiency compared to that of any man-made machine.It is important to remember that cellular or biochemical respiration is a continuous process. Although we tend to discuss it in three “steps,” these steps are not separate events. We have seen that electron transport is part of glycolysis when oxygen is available and that electron transport accounts for most of the ATP production in the Krebs citric acid cycle.Phosphorylation is the process for adding a phosphate to glucose during glycolysisPhosphoglyceraldehyde is the result of cleaving fructose diphosphate.Glycolytic breakdown of one glucose molecule provides two pyruvic acid molecules.The transition from C3 pyruvic acid to C2 acetyl-CoA has a first transitional conversion of acetic acidThe Krebs’ citric acid cycle produces five acids in transition; they are oxaloacetic, citric, alpha-ketoglutaric, succinic and malic.There are two situations when glucose is broken down in the absence of oxygen. One is when yeast cells (a type of fungus) feed on glucose, and this process is called fermentation. The other situation occurs in our muscle cells when we overexercise and experience muscle fatigue and cannot get enough oxygen to the muscle cells. Then the muscle cells begin to break down glucose in the absence of oxygen, a much less efficient breakdown with less ATP produced. We will now look at these two anaerobic processes.Fermentation is the process by which yeast breaks down glucose anaerobically (in the absence of oxygen). The final products of fermentation are: carbon dioxide gas (CO2), ethyl alcohol (CH3CH2OH) and ATP. In yeast cells, glucose breaks down, as in glycolysis, to produce two molecules of pyruvic acid, a net gain of two ATP and two NADH2. However, because oxygen is not used, the pyruvic acid molecules do not proceed to the citric acid cycle. Instead a yeast enzyme called a decarboxylase breaks down the pyruvic acid to CO2, and a C2 compound, acetaldehyde (ass-et-AL-deh-hyde) (CH3CHO). It is the CO2 gas that causes bread to rise and is the reason we add yeast to our flour (glucose), water and eggs (which makes dough) when we bake bread.Without Oxygen | Because this process occurs without oxygen, the NADH2 does not give its electrons to oxygen through the electron transport system as it does in aerobic respiration. Instead the NADH2 donates its two hydrogen atoms to the acetaldehyde through the action of another yeast enzyme called an alcoholic dehydrogenase. This reaction regenerates the NAD and forms the final product ethyl alcohol. This product is what is produced in the beer, wine and liquor industries to convert the sugars in grapes and the sugars in grains to alcohol. | | | | In conclusion, the fermentation process produces only two ATP per glucose molecule. Obviously, this energy-capturing mechanism is much less efficient than aerobic respiration. |
The second situation that can occur in anaerobic respiration is the breakdown of glucose in human muscle cells when not enough oxygen becomes available due to muscle fatigue such as when an athlete sprints. Again this process starts with glycolysis. However, the pyruvic acid formed undergoes a different fate. Again glycolysis yields two pyruvic acid molecules, a net gain of two ATP molecules, and two NADH2 per glucose molecule. As it was in fermentation, the two NADH2 cannot donate their electrons to oxygen. Instead the NADH2 donates them to pyruvic acid to form lactic (LAK-tik) acid.It is the accumulation of lactic acid that causes the momentary fatigue in muscles that are overexercised. When muscles are overworked, the muscle cells need to produce extra energy in the form of ATP. Aerobic respiration produces much of this energy. However, if the muscle is worked more rapidly than oxygen (O2) can be supplied to it from the bloodstream, the muscle cells will begin to produce the ATP anaerobically and lactic acid accumulates. Once oxygen gets to the muscle, the fatigue diminishes as lactic acid is broken down.

When we overexercise and our muscles get sore and we experience muscle fatigue, we notice that our heartbeat and breathing rate are accelerated. We sit down, breathe faster (to get more O2 into our bodies), and the soreness slowly diminishes. When O2 again becomes available, the lactic acid is converted back to pyruvic acid and aerobic respiration proceeds as normal. We note that anaerobic formation of ATP by muscles is much less efficient than aerobic respiration. Only two molecules of ATP are produced per glucose molecule.When yeast breaks down glucose, the resultant products are carbon dioxide gas, ethyl alcohol and ATP.During fermentation, the enzyme decarboxylase breaks down pyruvic acid and acetaldehyde. |
Anaerobic breakdown of glucose in muscle cells produces lactic acid.The process by which yeast cells break down glucose anaerobically is called: fermentation |

Obviously, we do not only eat glucose. So where do the other food compounds in our diet fit into the respiration cycle to produce ATP? If we think of the steps in biochemical respiration as parts of a very efficient cellular furnace where fuel (food) is converted to another form of chemical energy, ATP, then we can grasp a better understanding of how other food molecules are burned to produce ATP.Glucose is a simple carbohydrate. Other carbohydrates such as starch (plant carbohydrate) and glycogen (animal starch) as well as other types of sugars such as monosaccharides and disaccharides fit into the cellular furnace at the level where glucose enters the glycolytic sequence. If after digestion the food molecules are not needed immediately, they can be stored in the body (in food vacuoles or the liver, or converted to fat cells) until needed later to produce more ATP.Digestion decomposes fat into fatty acids and glycerol. They, too, will enter the cellular furnace at a stage related to their chemical structure. Glycerol, a C3 molecule, is similar to PGA and will enter at the PGA stage of glycolysis. Fatty acids enter the Krebs citric acid cycle.Proteins are broken down by digestion into amino acids. Again, they will enter the cellular furnace at a level related to their chemical structure. Alanine, a C3 amino acid, and lactic acid enter at the pyruvic acid stage. Glutamic acid, a C5 amino acid, is similar to alpha-ketogluteric acid. Aspartic acid, a C4 amino acid, resembles oxaloacetic acid. These amino acids enter into the citric acid cycle at different stages.

So when you put that piece of candy into your mouth during class break to get some extra energy to finish class, you now will have a better understanding of how that carbohydrate is converted to ATP, the fuel that runs our cells. The simplest way of describing cellular or biochemical respiration is to begin the process with a glucose molecule. Glycolysis occurs in the cytoplasm of the cell and produces pyruvic acid. If oxygen is available, the pyruvic acid is eventually converted to acetyl-CoA, which then enters the citric acid cycle, eventually being converted to CO2, H2O and 38 ATP. If oxygen is not available, the pyruvic acid is converted to lactic acid and only two ATP molecules are produced.Summary of ATP Production from One Glucose Molecule | The table summarizes products produced and the total ATP produced in the individual stages of the cellular metabolism of one glucose molecule. The stages are broken down into glycolysis, acetyl-CoA production and the citric acid cycle. |
Fatty acids and glycerol are products of fat digestion.Digestion breaks down protein into amino acidsCellular reproduction is the process by which a single cell duplicates itself. In this process the genetic material in the nucleus is duplicated during interphase of the cell cycle followed by the process called mitosis (my-TOH-sis) when the nuclear material is replicated. This is followed by duplication of the cellular organelles in the cytoplasm called cytokinesis (sigh-toh-kye-NEE-sis), which is the final event of mitosis leading to two new daughter cells. These processes, part of the cell cycle, allow our bodies to grow, repair themselves, and maintain our structures and functions. In other words, these processes allow us to maintain our life.However, cellular reproduction is also the process by which our genetic material is passed on to our offspring from one generation to the next. In this process of cellular reproduction, special cells called sex cells, the egg and the sperm, are produced. In this type of cellular reproduction, the genetic material must not only be duplicated, but it must also be reduced in half so that the female egg carries half of the genetic material or 23 chromosomes and the male sperm carries the other one half of the genetic material or the other 23 chromosomes. A special kind of cellular reduction division called meiosis (my-OH-sis), which occurs only in the gonads, allows this to occur. When a sperm and and egg unite in fertilization, the genetic material is returned to its full complement of 46 chromosomes.Meiosis occurs only in the gonads.A reduction division of the nuclear material so that each gamete contains only half as much hereditary material as the parent cell is known as: meiosisOne of the most significant discoveries in biology of the 20th century was the discovery of the three-dimensional structure of the DNA molecule. A number of scientists made various contributions to our knowledge of the DNA molecule. The molecule itself was discovered in 1869 by a German chemist, Friedrich Miescher. He extracted a substance from the nucleus of human cells and the sperm of fish. He called it nuclein because it came from the nucleus. Because this material was slightly acid, it became known as nucleic acid.It was not until the 1920s that any further discoveries were made. A biochemist, P. A. Levine, discovered that DNA contained three main components: 1. phosphate (PO4) groups, 2. five carbon sugars and nitrogen-containing bases called purines (adenine and guanine) 3. and pyrimidines (thymine and cytosine).The actual three-dimensional structure of DNA was discovered in the 1950s by three scientists. It was a British chemist, Rosalind Franklin, who discovered that the molecule had a helical structure similar to a winding staircase. This was accomplished when she conducted an x-ray crystallographic analysis of DNA. Her photograph was made in 1953 in the laboratory of another British biochemist, Maurice Wilkins.Two other researchers were also studying the DNA molecule at this time: James Watson, an American postdoctoral student, and an English scientist, Francis Crick, at Cambridge University in England. After learning informally of Rosalind Franklin’s discovery, they worked out the three-dimensional structure of the DNA molecule. Rosalind Franklin’s discovery of the helical nature of DNA was published in 1953, but Watson and Crick learned of her results before they were published. James Watson and Francis Crick won the Nobel Prize in 1962 after publishing their results. Rosalind Franklin, meanwhile, had tragically died of cancer prior to this event. Today, however, these three are given credit for discovering the structure of DNA, the molecule that contains all the hereditary information of an individual. An interesting account of the discovery of the nature of the molecule was published in 1968 by James Watson in his book The Double Helix. This discovery opened up whole new fields of research for the 20th century: recombinant DNA, the Human Genome Project and genetic engineering.

DNA (deoxyribonucleic acid) is the hereditary material of the cell. It not only determines the traits an organism exhibits, but it is exactly duplicated during reproduction so that offspring exhibit their parent’s basic characteristics. An organism’s characteristics are due to chemical reactions occurring inside our cells. DNA governs these chemical reactions by the chemical mechanism of controlling what proteins are made.Every DNA molecule is a double helical chain of nucleotides (noo-KLEE-oh-tides). A nucleotide consists of a phosphate group (PO4), a five-carbon sugar (deoxyribose) and an organic nitrogen-containing base, either a purine or a pyrimidine. There are two purines (PYOO-reenz), adenine (ADD-eh-neen) and guanine (GWAHN-een) and two pyrimidines (pih-RIM-ih-deenz), thymine (THYE-meen) and cytosine (SYE-toh-seen). Adenine always pairs up with thymine and guanine always pairs up with cytosine. Bonds form between the phosphate group of one nucleotide and the sugar of the next nucleotide. The organic nitrogen base extends out from the sugar of the nucleotide. It is easier to visualize the double helical nature of the DNA if we think of it as a spiral staircase. The handrails of the staircase are composed of the phosphate-sugar chain, and the stairs of the staircase are the nitrogen base pairs.If we look at the figure, we see that a pyrimidine always pairs with a purine. A pyrimidine is a single ring of six atoms (thymine and cytosine); a purine is a fused double ring of nine atoms (adenine and guanine). These organic nitrogen bases are a complex ring structure of carbon and nitrogen atoms. Because we know how the bases pair up in the double chain of nucleotides, if we only know one side of the helix, we can figure out the second side by matching bases. The two chains of the helix are held together by weak hydrogen bonds between the base pairs. There are two hydrogen bonds between the pyrimidine thymine and the purine adenine, whereas there are three hydrogen bonds between the pyrimidine cytosine and the purine guanine. Because of the specific pairing of bases, the sequence of bases in one chain determines the sequence of bases in the other. We therefore refer to the two chains as complements of each other. A gene is a sequence of organic nitrogen base pairs that codes for a polypetide or a protein.A major project of the 20th century that developed from Watson, Crick and Franklin’s discovery of DNA structure was the Human Genome Project. The objective of this project was to identify all the genes on all 46 chromosomes (DNA molecules). We know now that there are approximately 3 billion organic base pairs that code over 30,000 genes. We can think of the bases adenine (A), thymine (T), cytosine (C) and guanine (G) as the four letters of the alphabet of life. These base pairs determine all the characteristics of all the life we know on our planet-the basic structure of the DNA molecule is the same for all living organisms.The DNA molecule must be duplicated before cell division. The molecule separates where the hydrogen bonds hold the two chains of nucleotides together and a new copy of the DNA chain is constructed. The first step is the unwinding of the molecule. This is accomplished by helicase enzymes that separate the hydrogen bonds between the base pairs and stabilize the nucleotide chains of the double helix. Then new nucleotides are added to the separated chains by DNA polymerase, another enzyme. In this way, a copy of the DNA molecule is constructed.Levine discovered that DNA contained phosphate groups, five carbon sugars, purines and pyrimidines.Two purines in DNA are adenine and guanine.Two pyrimidines in DNA are thymine and cytosine.The four letters in the alphabet of life are A, C, T and G.All reproduction begins at the cellular level. The process by which a cell divides into two and duplicates its genetic material is called the cell cycle. The cell cycle is divided into three main stages: interphase (the stage in which great activity is occurring but this activity is not visible; thus, this stage used to be called a “resting stage”), mitosis and cytokinesis. Two of these three stages have substages. We shall discuss all stages in detail.The time to complete a cell cycle will vary greatly among different organisms. Cells in a developing embryo will complete the cell cycle in less than 20 minutes. A dividing mammalian cell will complete the cycle in approximately 24 hours. Other cells in our bodies rarely duplicate and undergo the cell cycle, such as nerve cells and muscle cells. Human liver cells will divide only if damaged. They usually have cell cycles lasting a full year.Refer to the figure for illustrations of the stages of the cell cycle discussed below. A cell spends most of its time in the stage of the cell cycle known as interphase. This phase, the longest and most dynamic part of a cell’s life, is not part of cell division. In fact, interphase means between phases. Yet during this time the cell is growing, metabolizing and maintaining itself. During this time, the nucleus is seen as a distinct structure surrounded by its nuclear membrane. Inside the nucleoplasm the unwound strands of chromosomes are only visible as dark threads called chromatin (KRO-mah-tin).Interphase has three subphases: growth one (G1), synthesis (S) and growth two (G2). Some authors called the G phases gap one and gap two.G1 is the primary growth phase of the cell. It occupies the major portion of the life span of the cell.The synthesis or S phase is when the strands of DNA duplicate themselves. Each chromosome now consists of two sister chromatids attached to each other at a central region called the centromere but are not yet visible. Most chromosomes consist of 60% protein and 40% DNA.The G2 phase is the final phase for the preparation of cell division. In animal cells, the centrioles finish replicating and each cell now has two pairs. Mitochondria are replicated as the chromosomes now condense and coil into tightly compacted bodies. Tubulin is synthesized. This is the protein material that forms the microtubules and assembles at the spindle.Mitosis is the process of cellular reproduction that occurs in the nucleus and forms two identical nuclei. Because of the intricate movement of daughter chromosomes as they separate, this phase of the cell cycle has received a great deal of study by biologists. This phase can also be easily observed with a light microscope. Although mitosis is a continuous process, it is subdivided into four stages: prophase, metaphase, anaphase and telophase (TELL-oh-faze). Refer to the figure for an illustration of the stages of mitosis. The cells resulting from mitosis are exact duplicates or clones of the parent cell.The coiled, duplicated chromosomes have shortened and thickened and are now visible. Each chromosome consists of two sister or daughter chromatids. The sister chromatids remain attached to one another at the centromere (SIN-troh-meer). The centromere is a constricted or pinched-in area of the chromosome where a disk of protein called the kinetochore (kye-NEE-toh-kor) is found.In animal cells, the centriole pair begins to move apart to the opposite poles of the cell forming a group of microtubules between them called the spindle fibers. In plant cells, a similar group of spindle fibers forms even though there are no centrioles.As the centrioles move apart to the opposite poles of the cell, they become surrounded by a cluster of microtubules of tubulin that radiate outward looking like a starburst. This starburst form is called the aster. The spindle fibers form between the asters. As these fibers form, they push the centrioles to the opposite ends of the cell and brace the centrioles against the cell membrane. At this time the nuclear membrane breaks down and its components become part of the endoplasmic reticulum. The nucleolus is no longer visible.Each chromosome has two kinetochores, one for each sister chromatid. As prophase continues, a group of microtubules grow from the poles to the centromeres of the chromosomes. The microtubules attach the kinetochores to the poles of the spindle. Because these microtubules coming from the two poles attach to opposite sides of the centromere, they attach one sister chromatid to one pole and the other sister chromatid to the other, thus ensuring separation of the sister chromatids, each one going to a different daughter cell.Metaphase is the second stage of mitosis and begins when the sister chromatids align themselves at the center of the cell. The chromosomes are lined up in a circle along the inner circumference of the cell called the equator of the cell. Held in place by the microtubules and attached to the kinetochore of their centromeres, the chromosomes become arranged in a ring at the equatorial or metaphase plate in the middle of the cell. At the end of metaphase each centromere now divides, separating the two sister chromatids of each chromosome.Anaphase is the shortest stage of mitosis and is one of the most dynamic stages to observe. The divided centromere, each with a sister chromatid, moves toward the opposite poles of the spindle. The motion is caused by the pulling of the microtubules on the kinetochore of each sister chromatid. The sister chromatids take on a V shape as they are drawn to their respective poles. At this time, the poles also move apart by microtubular sliding and the sister chromatids are drawn to opposite poles by the shortening of the microtubules attached to them. Cytokinesis, the division of the cytoplasm, may begin in anaphase.The final stage of mitosis is telophase. The sister chromatids, which now can be called chromosomes, begin to decondense and uncoil. Their V-shaped or sausage form disappears into diffuse chromatin, becoming long and thin. The spindle apparatus is disassembled as the microtubules are broken down into units of tubulin to be used to construct the cytoskeleton of the new daughter cells. A nuclear membrane forms around each group of daughter chromosomes. Cytokinesis is nearly complete. In animal cells the centrioles duplicate. Plant cells do not have centrioles.The process of cell division is not yet complete because the actual separation of the cell into two new daughter cells has yet to occur. The phase of the cell cycle in which actual cell division occurs is called cytokinesis.In animal cells, cytokinesis occurs as the cells separate by a furrowing in or pinching in of the cell membrane referred to as a cleavage furrow. The cell membrane indents to form a valley outside the spindle equator. This furrow first appears in late anaphase, and in telophase, it is drawn in more deeply by the contraction of a ring of actin filaments that lie in the cytoplasm beneath the constriction points. As constriction proceeds, the furrow extends into the center of the cell and thus the cell is divided into two.In plant cells, a cell plate forms at the equator. Small membranous vesicles form this cell plate, which grows outward until it reaches the cell membrane and fuses with it. Cellulose is then deposited in this new membrane forming a new cell wall that divides the cell in two.Each new daughter cell now enters the interphase stage of the cell cycle. Each now begins its growth phase until it is ready to divide once more.The process by which a cell divides into two and duplicates its genetic material is known as a: cell cycle |
A significant stage of the cell cycle in which the cell is growing, metabolizing, and maintaining itself and is not dividing is known as the: interphase
The process of cellular reproduction that occurs in the nucleus, forming two identical nuclei, is known as: mitosis
In sexual reproduction, two specialized cells (the sperm and the egg) known as gametes unite to form a fertilized egg or zygote. The advantage of sexual reproduction is the increased genetic variability that results from the uniting of the hereditary material of two different organisms. This results in a new individual, similar to but not identical to either parent. This new genetic variability gives the offspring a chance to adapt to a changing environment. To produce these special cells or gametes, a special kind of cellular division must occur. This special kind of division is called meiosis (mye-OH-sis) and it occurs only in special organs of the body-in the female gonads or ovaries and in the male gonads or testes.
Meiosis is a reduction division of the nuclear material so that each gamete contains only half as much hereditary material as the parent cell. When two gametes unite, the resulting zygote has the full complement of hereditary or DNA material. Humans have 46 chromosomes in our body cells; however, the human egg has only 23 and the human sperm has only 23 as a result of meiosis. This reduced number is called the haploid (HAP-loyd) (Greek haploos = one) or n number and the total or full complement of chromosomes is referred to as the 2n or diploid (DIP-loyd) (Greek di = two) number. The figure illustrates the sexual cycle. We inherited 23 chromosomes from our mother through the egg fertilized at conception and 23 from our father’s sperm. Meiosis consists of two separate divisions where chromosomes are separated from one another but the DNA is duplicated only once. The first meiotic division is broken down into four substages: prophase I, metaphase I, anaphase I and telophase I. It is in this first meiotic division that the chromosomes are reduced in half. | |

| The second meiotic division is also broken down into four substages: prophase II, metaphase II, anaphase II and telophase II. In meiosis we end up with four daughter cells each containing only half the genetic material, whereas in mitosis we end up with two daughter cells each containing the full complement of genetic material.The DNA has already duplicated before the onset of meiosis. Therefore, just like at the beginning of mitosis in interphase, each thread of DNA consists of two sister chromatids joined at their centromere. In prophase I, the duplicated chromosomes shorten, coil, thicken and become visible. It is here in meiosis that now something very different occurs. Each chromosome pairs up with its homologue. Remember that our 46 chromosomes exist as 23 pairs. One member of each pair was inherited from our mother and the other member of each pair from our father. In mitosis, look-alike chromosomes did not pair up with one another.In meiosis, homologous chromosomes are brought so close together that they line up side by side in a process called synapsis. We now have a pair of homologous chromosomes each with two sister chromatids. The visible pair of chromosomes is called a tetrad.The chromosomes are so close together that they may actually exchange genetic material in a process called crossing-over. Actual segments of DNA are exchanged between the sister chromatids of the homologous chromosomes. Crossing-over is a common but random event and it occurs only in meiosis. Evidence of crossing-over can be seen with a light microscope as an X-shaped structure known as a chiasma or chiasmata (key-AZZ-mah-tah) (plural). The spindle forms from microtubules just as in mitosis; paired chromosomes separate slightly and orient themselves on the spindle attached by their centromere.Spindle microtubules attach to the kinetochore only on the outside of each centromere, and the centromeres of the two homologous chromosomes are attached to microtubules originating from opposite poles. This one-sided attachment in meiosis is in contrast to mitosis whose kinetochore on both sides of a centromere are held by microtubules. This ensures that the homologous chromosomes will be pulled to opposite poles of the cell. The homologous chromosomes line up on the equatorial plate. The centromeres of each pair lie opposite one another. The orientation on the spindle is random thus either homologue might be oriented to either pole.The microtubules of the spindle shorten and pull the centromeres toward the poles, dragging both sister chromatids with it. Thus, unlike mitosis, the centromere does not divide in this stage. Because of the random orientation of the homologous chromosomes on the equatorial plate, a pole may receive either homologue of each pair. Thus, the genes on different chromosomes assort independently.The homologous chromosome pairs have separated and now a member of each pair is at the opposite ends of the spindle. Now at each pole is a cluster of “haploid” chromosomes. The number has been reduced from 46 to 23 at each pole. However, each chromosome still consists of two sister chromatids attached by a common centromere. This “duplication condition” will be corrected in the second meiotic division. Now the spindle disappears, the chromosomes uncoil and become long and thin and a new nuclear membrane forms around each cluster of chromosomes at the opposite poles. Cytokinesis occurs and we have two new cells formed at the end of the first meiotic division. The second meiotic division closely resembles the occurrences in mitosis.In each of the two daughter cells produced in the first meiotic division, a spindle forms, and the chromosomes shorten, coil and thicken. The nuclear membrane disappears but no duplication of DNA occurs.In each of the two daughter cells, the chromosomes line up on the equatorial plate. Spindle fibers bind to both sides of the centromere. Each chromosome consists of two sister chromatids and one centromere.The centromeres of the chromosomes divide. The spindle fibers contract, pulling the sister chromatids apart and moving each one to an opposite pole. Now each chromosome is truly haploid, consisting of one chromatid and one centromere.New nuclear membranes form around the separated chromatids, the spindle disappears, and the chromosomes uncoil and decondense. The result is four haploid daughter cells each containing one-half the genetic material of the original parent cell, or, in our case, each cell having 23 chromosomes instead of 46.The four haploid cells produced by meiosis are not yet mature sex cells. Further differentiation must now occur. This is known as gametogenesis (gam-eh-toh-JEN-eh-sis).The process occurring in the semiferous tubules of the testes is called spermatogenesis (sper-mat-oh-JEN-eh-sis). The cytoplasm of each of the four cells produced, called spermatids, becomes modified into a tail-like flagellum. A concentration of mitochondria collect in the middle piece or collar. The mitochondria will produce the ATP necessary to propel the flagellum, which causes the sperm to swim. The nucleus of each cell becomes the head of the sperm. The genetic material is concentrated in the head of the sperm. The sperm cell will penetrate an egg and fuse with the genetic material of the egg in the process called fertilization, producing a fertilized egg or zygote.

The formation of the female egg, called oogenesis (oh-oh-JEN-eh-sis), occurs in the ovary. However, only one functional egg is produced. In the first meiotic division, there is an unequal distribution of the cytoplasm so that one cell is larger than the other. The larger cell in the second meiotic division also has unequal distribution of the cytoplasm. The three smaller cells produced are called polar bodies and eventually die. They have contributed cytoplasm to the single larger cell that will become the functional egg. The union of sperm and egg is called fertilization and restores the diploid number of chromosomes to 46.A reduction division of the nuclear material so that each gamete contains only half as much hereditary material as the parent cell is known as: meiosisThe formation of the male sex cell is known as: spermatogenesisThe formation of the female sex cell is known as: oogenesisThe stage of meiosis in which the centromeres of the chromosomes divide is: anaphase IIJulio is in Anatomy lab looking at a slide covered with cells. He is trying to find a cell in metaphase. What distinctive feature is found in a metaphasic cell? The chromosomes line up along the equator of the cell on the metaphase plate.The two types of cellular division consisting of mitosis and meiosis are easy to confuse. They have similarities but they also have differences. In both mitosis and meiosis, the chromosomes duplicate or replicate in the phase of the cell cycle called interphase. However, in mitosis the end result is two daughter cells each with exactly the same number of chromosomes as the parent cell, whereas in meiosis the end result is four daughter cells each with only half the number of chromosomes as the parent cell. Mitosis consists of one division, whereas meiosis consists of two divisions.In mitosis, when the genetic material duplicates, the homologous chromosomes are scattered in the nucleus and do not seek one another out. In meiosis, after duplication, the homologous pairs of chromosomes line up together and come so close that they entwine. Crossing-over or exchange of segments of DNA may occur. Crossing-over occurs only in prophase I of meiosis. This results in a recombination of existing genes, thus producing new genetic characteristics. In mitosis the centromere divides in anaphase. In meiosis the centromere does not divide in anaphase I. The centromere divides only in anaphase II. The figure on the right provides a summary comparison of mitosis and meiosis.Mitosis occurs in all cells of our bodies on a regular basis (except nerve, muscle and liver cells). After the egg is fertilized, the embryo develops by mitosis. After birth, we grow and mature by mitosis. When we cut our finger or bruise our tissues, the cells are repaired and replaced by mitosis. Liver cells divide only if damaged; muscle cells and nerve cells rarely divide by mitosis. Cells produced by mitosis can live on their own. These cells all contain the same genetic information as the parent cell. In special sections of our gonads, the seminiferous tubules of the testes of the male and in the ovaries of the female, another kind of cell division occurs.Meiosis occurs only in these special cells of the gonads. It is a reduction division. The genetic material is reduced in half. This process begins at puberty in the male and in the embryo of the female. It will continue at puberty in the female. The cells produced cannot live on their own. They live for only a short time and eventually die unless they fuse in fertilization inside the female reproductive tract.In each type of cellular division, the genetic material is exactly duplicated during interphase. Sometimes, however, the genetic material may be damaged by x-rays, radiation or certain chemicals. When this happens, the cells’ damaged genetic material may cause them not to go into interphase. They divide continuously, forming masses of tissues. This is cancer.Cancerous cells that have left the tumor site and traveled to other parts of the body are known as: metastasesA malignant tumor developing from epithelial tissue is called a: carcinomaDuncan has his father’s nose and his mother’s chin. What cellular process produced the cells that combined to give him these features? MeiosisCHAPTER 5The basic units of tissue (TISH-you) are groups of cells. These cells will have a similar function and a similar structure. Tissues are classified based on how these cells are arranged and what kind and how much material is found between the cells. Cells are either tightly packed or separated by interstitial material. The study of tissue is called histology (hiss-TALL-oh-jee). The four basic types of tissue are: 1. epithelial 2. connective 3. muscle 4. nervous | | Each type is further subdivided into specific examples. These tissues combine to form organs. The various organs make up the systems of the body that allow us to function and survive in our complex world. |
Groups of cells with similar function form tissuesThe four types of tissue in the human body are connective, muscle, nervous and epithelialEpithelial (ep-ih-THEE-lee-al) tissue functions in four major ways: 1. It protects underlying tissues. 2. It absorbs. 3. It secretes. 4. Epithelial tissue excretes. Sweat glands excrete waste products such as urea.Our skin is epithelial tissue and protects us from the harmful rays of the sun and certain chemicals. The lining of our digestive tract is made of epithelial tissue and protects underlying tissue from abrasion as food moves through the tract.In the lining of the small intestine, nutrients from our digested food enter blood capillaries and get carried to the cells of our body.All glands are made of epithelial tissue; the endocrine glands secrete hormones, the mucous glands secrete mucus and our intestinal tract contains cells that secrete digestive enzymes in addition to the pancreas and the liver, which secrete the major portions of digestive enzymes.When epithelial tissue has a protective or absorbing function, it is found in sheets covering a surface, like the skin or intestinal lining. When it has a secreting function, the cells involute from the surface into the underlying tissues to form glandular structures. Only a minimal, if any, amount of intercellular material is found in epithelial tissue. The cells are very tightly packed together and thus this tissue is not as easily penetrated as other tissues.Epithelial cells are anchored to each other and to underlying tissues by a specialized membrane called the basement membrane. This membrane acts like the adhesive on a tile floor, the tiles being the epithelial cells. It is very important because it acts as an anchor for the attached side of the epithelial cells and it provides protection for other underlying tissue like connective tissue.Epithelial tissue can be named according to shape and structures that might be on the free or outer edge of the cells. This surface can be plain or it can have rows of cilia (those that line the respiratory tract), a flagellum (the sperm cell), microvilli (folds) and secretory vesicles (those that line the small intestine). Epithelial tissue can be one layer or several layers thick.Epithelial cells are classified as either: 1. squamous 2. cuboidal 3. columnarSquamous (SKWAY-mus) cells are flat and slightly irregular in shape. They serve as a protective layer. They line our mouth, blood and lymph vessels, parts of kidney tubules, our throat and esophagus, the anus and our skin. If exposed to repeated irritation like the linings of ducts in glands, other epithelial cells can become squamous in appearance.Cuboidal (KYOO-boyd-al) cells look like small cubes. They are found in glands and the lining tissue of gland ducts (sweat and salivary), the germinal coverings of the ovaries and the pigmented layer of the retina of the eye. Their function can be secretion and protection. In areas of the kidney tubules, they function in absorption.Columnar cells are tall and rectangular looking. They are found lining the ducts of certain glands (e.g., mammary glands) and the bile duct of the liver. They are also found in mucus-secreting tissues such as the mucosa of the stomach, the villi of the small intestine, the uterine tubes and the upper respiratory tract. Many of these cells are ciliated.The four most common arrangements of epithelial cells are simple, stratified, pseudostratified and transitional. As epithelial cells are named, a combination of the classification of both shape and arrangement is used.The simple arrangement is one cell layer thick. It is found in the lining of blood capillaries, the alveoli of the lungs and in the loop of Henle in the kidney tubules. Refer to the figures on the right for simple cuboidal epithelium found in the lining of glandular ducts. Refer to the figure on the right for simple columnar epithelium found in the villi of the small intestine and the lining of the uterus.The stratified arrangement is several layers of cells thick. Refer to the figure on the right for stratified squamous epithelium found lining our mouth and throat and as the outer surface of our skin. Stratified cuboidal epithelium is found lining our sweat gland ducts and salivary gland ducts. Stratified columnar epithelium is found as the lining of the ducts of the mammary glands and in parts of the male urethra.The pseudostratified arrangement appears to consist of several layers due to nuclei variously positioned in the cell, but, in actuality, all cells extend from the basement membrane to the outer or free surface of the cells. This arrangement is usually seen with columnar cells. The figure on the right is an example of pseudostratified ciliated, columnar epithelium. We find this tissue in the throat, trachea and bronchi of the lungs.Transitional epithelium consists of several layers of closely packed, flexible and easily stretched cells. When the surfaces of the cells are stretched, as in a full bladder, the cells appear squamous or flat but when the tissue is relaxed, as in an empty bladder, the layers of cells look ragged like the teeth of a saw. This type of epithelium lines the pelvis of the kidney, the ureters, the urinary bladder and the upper part of the urethra.Epithelial tissue can also be named or classified based on its function. The terms mucous membrane, glands, endothelium and mesothelium all refer to epithelial tissue.Mucous (MYOO-kus) membrane lines the digestive, respiratory, urinary and reproductive tracts. It lines all body cavities that open to the outside. It is usually ciliated. Its most obvious function is to produce mucus, but it also concentrates bile in the gallbladder. It secretes enzymes for the digestion of food and nutrients before absorption. Mucous membrane protects, absorbs nutrients and secretes mucus, enzymes and bile salts.Glandular epithelium forms glands. Glands are involutions of epithelial cells specialized for synthesizing special compounds. The body has two types of multicellular glands: 1. Exocrine 2. EndocrineExocrine (EKS-oh-krin) glands have excretory ducts that lead the secreted material from the gland to the surface of a lumen (passageway) on the skin. There are two types of exocrine glands.Simple exocrine glands have single unbranching ducts. Some examples of simple exocrine glands are the sweat glands, most of the glands of the digestive tract and the sebaceous glands. The other type of exocrine gland is the compound exocrine gland. These glands are made of several component lobules each with ducts that join other ducts. Thus, the ducts are branching. Examples of compound exocrine glands are the mammary glands and the large salivary glands.Endocrine glands are the second type of multicellular glands in the body. They are ductless and secrete hormones; examples are the thyroid and pituitary glands. Goblet cells are unicellular glands that secrete mucus. They are interspersed among the epithelial cells that make up mucous membranes.
Endothelium (en-doh-THEE-lee-um) is a special name given to the epithelium that lines the circulatory system. This system is lined with a single layer of squamous-type cells. Endothelium lines the blood vessels and the lymphatic vessels. The endothelium that lines the heart gets another special name and is called endocardium. A blood capillary consists of only one layer of endothelium. It is through this single layer of cells that oxygen, carbon dioxide, nutrients, and waste are transported by the blood cells to the various cells of our bodies.Our final type of epithelial tissue based on function is mesothelium (mezo-THEE-lee-um). This tissue is also called serous (SEER-us) tissue. It is the tissue that lines the great cavities of the body that have no openings to the outside. These membranes consists of a simple squamous cell layer overlying a sheet of connective tissue. Special names are associated with this type of epithelial tissue also. The pleura (PLOO-rah) is the serous membrane or mesothelial tissue that lines the thoracic cavity. The pericardium is the serous membrane that covers the heart; the peritoneum (pair-ih-toh-NEE-um) is the serous membrane lining the abdominal cavity. This tissue protects, reduces friction between organs and secretes fluid. The term parietal refers to the walls of a cavity and visceral refers to the covering on an organ.The four functions of epithelial tissue are protection of underlying tissue, absorbtion of nutrients, secretion of hormones and mucus, and excretion of urea.Tall and rectangular cells are called columnar.A simple arrangement of epithelial cells can be found in the kidneys, blood vessels and lungs.The epithelial cell arrangement found lining the throat is called stratified.
Mucous membranes are usually ciliated.The tissue lining the circulatory system is endothelium.Epithelial cells are anchored to each other and to underlying tissues by a specialized membrane called the: basement membraneGlands with ducts that lead the secreted material away from the gland to the surface of a passageway or the skin are known as: exocrine glandsDuctless glands that secrete hormones are called: endocrine glandsThe endothelium that lines the heart is called the: endocardiumThe serous membrane that lines the entire abdominal cavity is the: peritoneumtissue that lines the urinary bladder Which tissue type would that be? EpitheliumThe second major type of tissue is connective tissue. This type of tissue allows movement and provides support for other types of tissue. In this tissue, unlike epithelial, there is an abundance of intercellular material called matrix (MAY-trikz). This matrix is variable in both type and amount. It is one of the main sources of differences between the different types of connective tissue. There are also fibers of collagen (KOL-ah-jen) and elastin (ee-LASS-tin) embedded in this matrix. Sometimes the fibers are very apparent under the microscope, as in a tendon, whereas in other tissues the fibers are not very apparent as in certain cartilage.We can classify connective tissue into three subgroups: 1. loose connective tissue 2. dense connective tissue 3. specialized connective tissueAs the name implies, the fibers of loose connective tissue are not tightly woven among themselves. There are three types of loose connective tissue: 1. areolar (ah-REE-oh-lah) 2. adipose (ADD-ih-pohz) 3. reticular (reh-TIK-you-lar)Areolar is the most widely distributed of the loose connective tissue. It is easily stretched yet resists tearing. This tissue has three main types of cells distributed among its delicate fibers: 1. fibroblasts 2. histiocytes 3. mast cellsFibroblasts (FYR-broh-blastz) are small flattened cells with large nuclei and reduced cytoplasm; they are also somewhat irregular in shape. The term fibroblast (blast meaning germinal or embryonic) refers to the ability of these cells to form fibrils (small fibers). They are active in the repair of injury.Histiocytes (HISS-tee-oh-sightz) are large, stationary phagocytic (fag-oh-SIH-tik) cells that eat up (phago = eat) debris and microorganisms outside the blood circulatory system. They function like some white blood cells (the leukocytes) do in the blood. When they are motile, they are called macrophages (MACK-roh-fay-jez). A macrophage of loose connective tissue is specifically called a histiocyte. Histiocytes are stationary or fixed in tissue.Mast cells are roundish or polygonal in shape and are found close to small blood vessels. Mast cells function in the production of heparin (an anticoagulant) and histamine (an inflammatory substance produced in response to allergies).Areolar tissue is the basic support tissue around organs, muscles, blood vessels and nerves. It forms the delicate membranes around the spinal cord and brain. It attaches the skin to its underlying tissues.Adipose tissue is the second type of loose connective tissue. It is loaded with fat cells. Fat cells are so full of stored fat that their nuclei and cytoplasm are pushed up against the cell membrane. In a histologic section under a microscope, they look like large soap bubbles and are very easy to recognize. Adipose tissue acts as a firm, protective packing around and between organs, bundles of muscle fibers and nerves, and it supports blood vessels. The kidneys have a surrounding layer of adipose tissue to protect them from hard blows or jolts. In addition, because fat is a poor conductor of heat, adipose tissue acts as insulation for the body, protecting us from excessive heat losses or excessive heat increases in temperature.Think of the animals in the Arctic and Antarctic. They can live there because of their layers of blubber, which is adipose tissue. The camel’s hump is not a water storage organ but a thick hump of fat containing adipose tissue to protect the animal’s internal organs from the heat of the desert.Reticular tissue is the third type of loose connective tissue. It consists of a fine network of fibers that form the framework of the liver, bone marrow and lymphoid organs such as the spleen and lymph nodes.Again as the name implies, dense connective tissue is composed of tightly packed protein fibers. It is further divided into two subgroups based on how the fibers are arranged and the proportions of the tough collagen and the flexible elastin fibers. Examples of dense connective tissue having a regular arrangement of fibers are tendons, which attach muscle to bone, ligaments, which attach bone to bone, and aponeuroses (ap-oh-noo-ROH-sis), which are wide flat tendons. Tendons have a majority of tough collagen fibers, whereas ligaments (e.g., the vocal cords), have a combination of tough collagen and elastic elastin fibers.Examples of dense connective tissue having an irregular arrangement of these fibers are muscle sheaths, the dermis layer of the skin and the outer coverings of body tubes like arteries. Capsules that are part of a joint structure also have dense irregular connective tissue as do fascia (FASH-ee-ah), the connective tissue covering a whole muscle.A number of types of connective tissue have specialized functions. Cartilage is one of these special kinds of tissues. The three types of cartilage found in the body are hyaline, fibrous and elastic. Cells of cartilage are called chondrocytes (KON-droh-sightz); they are large round cells with spherical nuclei. When we view cartilage under the microscope, these chondrocytes are found in cavities called lacunae (lah-KOO-nee). The lacunae are cavities in a firm matrix composed of protein and polysaccharides. Depending on the type of cartilage, various amounts of collagen and elastin fibers are embedded in the matrix, causing the cartilage to be either flexible or very strong and resistant.Hyaline cartilage, when viewed under the microscope, has a matrix with no visible fibers in it, hence the name hyaline, which means clear. As the fetus forms in the womb, the skeletal system is made entirely of hyaline cartilage and is visible after the first 3 months of pregnancy. Most of this hyaline cartilage is gradually replaced by bone over the next 6 months through a process called ossification. However, some hyaline cartilage remains as a covering on the surfaces of the bones at joints. In our bodies, the costal cartilages that attach the anterior ends of our upper seven pair of ribs to the sternum is hyaline cartilage. The trachea and bronchi are kept open by incomplete rings of hyaline cartilage. The septum of our nose is also made of hyaline cartilage.In our bodies, the costal cartilages that attach the anterior ends of our upper seven pair of ribs to the sternum is hyaline cartilage. The trachea and bronchi are kept open by incomplete rings of hyaline cartilage. The septum of our nose is also made of hyaline cartilage.Fibrocartilage has a majority of tough collagenous fibers embedded in the matrix. These fibers make this type of cartilage dense and very resistant to stretching. The intervertebral disks that surround our spinal cord and act as shock absorbers between our vertebrae are made of this strong cartilage. It also connects our two pelvic bones at the pubic symphysis. Thus, we can flex our vertebral column and bend within a particular range of movement. During delivery, a minimal range of expansion of the birth canal can occur at the pubic symphysis due to the fibrocartilage.
The third type of cartilage is elastic cartilage. This type of cartilage has a predominance of elastin fibers embedded in the matrix. These fibers must be specially stained to view under a microscope. These fibers permit this type of cartilage to be easily stretched and flexible while being capable of returning to its original shape. Elastic cartilage makes up our external ear or auricle, our ear canals or auditory tubes and our epiglottis.
Bone is very firm specialized connective tissue. Bone is covered in great detail in Chapter 7. If we section a bone we see that it is composed of two types of bone tissue: compact bone, which forms the dense outer layer of bone and looks solid, and cancellous bone, which forms the inner spongy-looking tissue underneath the compact bone. When viewed under a microscope, the bone cells called osteocytes (OSS-tee-oh-sightz) are also found in cavities or lacunae as we saw in cartilage. However, the matrix of bone is impregnated with mineral salts, particularly calcium and phosphorous, which give bone its firm, hard appearance.
Another specialized connective tissue is dentin, the material that forms our teeth. Dentin is closely related to bone in structure but is harder and denser. The crown of the tooth is covered with another material, enamel, which is white in appearance. Dentin is light brown. If you ever chipped a tooth, the brown material you saw under the white enamel was the dentin. The enamel is secreted onto the dentin of a tooth by special epithelial cells that make up the enamel organ. This secretion occurs just before the teeth break their way through the gums.Blood and hematopoietic (hee-MAT-oh-poy-eh-tik) tissue are other examples of specialized connective tissue. Blood is unique connective tissue in that it is composed of a fluid portion (the plasma) and the formed elements of blood: the erythrocytes (eh-RITH-roh-sightz) or red blood cells and leukocytes (LOO-koh-sightz) or white blood cells. We will discuss blood in more detail in Chapter 13. Blood cells are formed in red bone marrow, and some white blood cells are also formed in lymphoid organs. Marrow and lymphoid organs are referred to as hematopoietic tissue. Blood is liquid tissue circulating through the body. It transports oxygen, nutrients, hormones, enzymes and waste products such as carbon dioxide gas and urea. It also protects the body through its white blood cells and helps to regulate body temperature.Lymphoid tissue is another specialized connective tissue. Lymphoid tissue is found in the lymph glands or nodes, the thymus gland, the spleen, the tonsils and the adenoids. Lymph tissue manufactures plasma cells like the B lymphocytes. This tissue’s main role is antibody production and protects us from disease and foreign microorganisms.The reticuloendothelial (reh-tik-you-loh-in-doh-THEE-lee-al) or RE system consists of those specialized connective tissue cells that do phagocytosis. Three types of cells fit into this category. The first type are the RE cells that line the liver (they get another special name: Kupffer cells), and those that line the spleen and bone marrow. The second type are the macrophages. These cells are also referred to as histiocytes or “resting-wandering” cells, because they are fixed in tissue until they must wander to an invader and devour it. Any phagocytic cell of the RE system can be called a macrophage. The third type of cell is a neuroglia (noo-roh-GLEE-ah) or microglia (my-KROG-lee-ah) cell. This is a phagocytic cell found in the central nervous system.Synovial membranes line the cavities of freely moving joints and are also classified as specialized connective tissue. These membranes also line bursae, which are small sacs containing synovial fluid found between muscles, tendons, bones and skin and underlying structures. They prevent friction where one organ overlies or moves over another.Connective tissue has many and varied functions: 1. Support 2. Nourishment 3. Transportation 4. Connection 5. Movement 6. Protection 7. Insulation 8. Storage 9. Attachment and separation Support | 10. | Bones support other tissues of the body. On top of bones we find muscle, nerves, blood vessels, fat and skin. Cartilage supports our nose and forms the bulk of the structure of our ear. | 11. Nourishment | 12. Blood carries nutrients to the cells of our body. Synovial membranes in joint capsules nourish the cartilage found on top of bones. | 13. Transportation | 14. | Blood transports gases, enzymes and hormones to cells. | Connection | | Tendons connect muscles to bone, and ligaments connect bone to bone. | | Movement | | Muscles pull on bones, and bones move our bodies through our environment. | | Protection | | Bones protect vital organs of the body like the heart, lungs, brain and spinal cord. Blood cells, especially the white blood cells, protect us from foreign microorganisms and tissue injury. |
Insulation, Storage, Attachment and Separation | Insulation | | Adipose tissue (fat) insulates us from excessive heat loss and excessive increases in temperature. | | Storage | | Bone stores the mineral salts calcium and phosphorous. Adipose tissue stores the high-energy molecules of fat to be used and converted to adenosine triphosphate when necessary. | | Attachment and separation | | Connective tissue attaches skin to underlying muscle. It also forms layers around and between organs. |
The type of tissue providing for movement and support is connectiveThis type of tissue has intercellular material called a matrixConnective tissue has the subgroups called loose, dense and specializedThe most widely distributed loose connective tissue is areolarThe three main types of areolar cells are the irregularly-shaped fibroblasts, the large stationary histiocytes and the polygonal-shaped mast cellsAdipose tissue is fat.Dense connective tissues bearing a regular arrangement of fibers are tendonsAdipose tissue acts as a firm, protective packing around and between organs, bundles of muscle fibers, and nerves.Elastic cartilage is the type of cartilage that is easily stretched and flexible.Dentin is the specialized connective tissue that forms our teeth.Large, stationary phagocytic cells that eat up debris and microorganisms outside the blood circulatory system are called: histiocytesA loose connective tissue forming the framework of the liver, bone marrow and lymphoid organs is known as: reticular tissueA type of cartilage that is dense and very resistant to stretching is known as: fibrocartilageThe type of cartilage that is easily stretched and flexible while being capable of returning to its original shape is known as: elastic cartilageThe specialized connective tissue that has a main role of antibody production and protection from disease and foreign microorganisms is: lymphoid tissueThe loose connective tissue cells that function in the production of heparin and histamine are: mast cellsThe connective tissue covering a whole muscle is called: fasciaA specialized connective tissue cell found in the central nervous system is known as: neuroglianose Which tissue type(s) would likely be affected? Bone, cartilage, epithelial (also blood)The basic characteristic of muscle tissue is its ability to shorten and thicken or contract. This is due to the interaction of two proteins in the muscle cell: actin and myosin. Muscle cell contractility is discussed in greater detail in Chapter 9. Because a muscle cell’s length is much greater than its width, muscle cells are frequently referred to as muscle fibers. The three types of muscle tissue are: 1. smooth 2. striated or skeletal 3. cardiacSmooth muscle cells are spindle-shaped with a single nucleus. They are not striated (STRYE-ate-ed), that is, you do not see alternating dark and light bands when viewed under the microscope. This muscle tissue is involuntary, meaning we do not control its contraction. It is controlled by the autonomic nervous system.We find smooth muscle in the walls of hollow organs like those of the digestive tract, arteries and veins. The muscle cells are arranged in layers: an outer longitudinal layer and an inner circular layer. Simultaneous contraction of the two layers pushes materials inside the hollow organs in one direction. Hence, food is pushed by contraction of the smooth muscles along the digestive tract, called peristalsis (pair-ih-STALL-sis), and blood is pushed along in arteries and veins. Urine is also pushed down the ureters from the kidneys by contraction of smooth muscle.Striated or skeletal muscle is the muscle we normally think about when we mention muscle. It is the tissue that causes movement of our body by pulling on bones, hence the name skeletal muscle. The long thin cells of skeletal muscle are multinucleated and striated. We can see alternating light bands of the thin protein filaments of actin and dark bands of the thick protein filaments of myosin. When we eat “meat” of animals and fish, it is usually muscle that we are consuming. Muscle makes up about 40% of our total weight and mass. Striated muscle is voluntary and is under the control of the central nervous system.Cardiac muscle is found only in the heart. Like skeletal muscle it is striated and like smooth muscle it is uninucleated and under the control of the autonomic nervous system. The cells of cardiac muscle are cylindrical in shape with branches that connect to other cardiac cells. These branches connect with one another through special areas called intercalated (in-TER-kah-lay-ed) disks. The cells are much shorter than either skeletal or smooth muscle cells. This is the muscle that causes contraction or beating of the heart; thus, it pumps the blood through our body. The interconnected branches of cardiac muscle cells guarantee coordination of the pumping action of the heart.Three types of muscle tissue are smooth (spindle-shaped), skeletal (or striated) and cardiac (only in the heart).The muscles responsible for moving the bones of the body are known as skeletal muscles.Muscle tissue that is under the control of the autonomic nervous system is known as what type of muscle tissue? involuntary muscle tissueWhich will likely heal faster-the ligaments or the bone? Why?
The bone will heal faster because it is more vascular-more blood vessels bring in more oxygen and nutrients to help heal.The basic unit of organization of nervous tissue is the nerve cell or neuron (NOO-ron). Actually, the neuron is a conducting cell, whereas other cells of the system called neuroglia are supporting cells. These different types of nerve cells are discussed in greater detail in Chapter 10. Neurons are very long cells, so like muscle cells, they are called nerve fibers.
It is basically impossible to view an entire neuron even under low power of the microscope due to their length. However, we can view the parts of a neuron as we scan a microscope slide. The cell body contains the nucleus. It also has rootlike extensions called dendrites (DEN-drytz) that receive stimuli and conduct them to the cell body. Axons (AK-sonz) are long, thin extensions of the cell body that transmit the impulse toward the axon endings.Nervous tissue makes up the brain, spinal cord, and various nerves of the body. It is the most highly organized tissue of the body. It controls and coordinates body activities. It allows us to perceive our environment and to adapt to changing conditions. It coordinates our skeletal muscles. Its special senses include sight, taste, smell and hearing. It controls our emotions and our reasoning capabilities. It allows us to learn through the memory process.A neuron consists of a long thin axon, a cell body and a root-like extension called a(n) dendriteThe basic unit of organization of nervous tissue is the nerve cell or neuron |
CHAPTER 6
The integumentary system is made up of the skin and its appendages. The appendages or modifications of the skin are hair, nails, sebaceous, ceruminous and sweat glands. The word “integument” means a covering, and the skin of an average adult covers well over 3000 square inches of surface area of the body.
The skin weighs about 6 pounds (this is nearly twice the weight of the brain or the liver). It receives approximately one-third of all the blood circulating through the body. It is flexible yet rugged and under normal conditions can repair and regenerate itself. Our skin is almost entirely waterproof. It protects us from the harmful ultraviolet rays of the sun through special pigment-producing cells. It is an effective barrier to most harmful chemicals, keeping them from entering our internal environment. It participates in the dissipation of water through sweating and helps regulate our body temperature.
Our skin consists of two main layers. The epidermis (ep-ih-DER-mis) is a layer of epithelial tissue that can further be divided into sublayers. It is found on top of the second layer of the skin called the dermis. This is a layer of dense connective tissue that connects the skin to tissues below it, like fat and muscle. Beneath the dermis is the subcutaneous layer.
The outermost or epidermal layer of the skin is composed of stratified, squamous, keratinized (no nucleus) epithelial cells. These cells are held together by highly convoluted, interlocking cellular links called desmosomes (DEZ-meh-somz). These desmosomes are responsible for the unique flexibility, entirety and whole continuous structure of the skin. The epidermis is thickest where it receives the most abrasion and weight-on the palms of the hands and the soles of the feet. It is much thinner over the ventral surface of the trunk.
The epidermis, which is not vascularized, rests on a basement membrane. The lowermost cells on this membrane divide by mitosis, so new cells push older cells up toward the surface. As they move up, they change shape and chemical composition because they lose most of their water and eventually die. This process is called keratinization (kair-ah-tin-ih-ZAY-shun) because the cells become filled with keratin (KAIR-ah-tin), a protein material. These dead, outermost cells are constantly being shed. This outermost layer forms an effective barrier to substances that would penetrate the skin, and this layer is very resistant to abrasion.
One of the ways the skin helps regulate body temperature is through the evaporation of sweat.
The epidermis is a layer of epithelial tissue.
The second layer is the dermis
The dermis is a layer of connective tissue
The skin is thickest on the palms of the hands and the soles of the feet.
As cells move up from the basement membrane, they eventually die
The protein material of hair and nails is keratin
The process of older epidermal cells moving up toward the surface, changing their shape and chemical composition, and becoming hardened as they fill with keratin is known as: Keratinization
The Stratum Corneum | 1. It consists of dead cells converted to protein or keratinized cells that constantly are being shed. 2. It is a barrier to light and heat waves, most chemicals and microorganisms. | | |

| The Stratum Lucidum | | |

| This layer is only one or two flat and transparent layers of cells thick. It is difficult to see. | | |

| The Stratum Granulosum | | |

| This layer is two or three layers of cells very active in keratinization. | | |

| The Stratum Spinosum | | |

| This layer consists of several layers of spiny-shaped polyhedron-like cells. | | |

| The interlocking cellular bridges or desmosomes are found in this layer. | | |

| The Stratum Germinativum 1. This layer rests on the basement membrane. Its lowermost layer of cells is called the stratum basale. 2. This layer is the layer that produces new epidermal cells by mitosis. 3. Melanocytes of this layer produce melanin. This pigment is responsible for skin color and protection from the harmful ultraviolet rays of the sun. 4. Dark-skinned individuals have more active melanocytes. 5. Albinism is a genetic condition that results from the absence of melanin. | | |

| The Dermis 1. The dermis is also called the corium or true skin and is composed of dense connective tissue. 2. Blood and lymph vessels, nerves, muscles, glands and hair follicles are found in the dermis. 3. It is divided into two portions: the papillary portion below the epidermis and the reticular portion above the subcutaneous tissue. 4. The subcutaneous tissue can be called the hypodermis. |

The process of keratinization produces distinctive layers of the epidermis called strata (plural) or stratum (STRAT-um) [singular]). There are five layers from outermost to deep. They are: 1. the stratum corneum (STRAT-um COR-nee-um), commonly called the horny or leathery layer 2. the stratum lucidum (STRAT-um LOO-sid-um), commonly called the clear layer 3. the stratum granulosum (STRAT-um gran-you-LOH-sum), commonly called the granular layer 4. the stratum spinosum (STRAT-um spye-NOH-sum), commonly called the spiny or prickly layer. 5. the innermost layer and the most important is the stratum germinativum (STRAT-um jer-mih-NAY-tih-vum) or the regenerative layer.

The stratum corneum forms the outermost layer of the epidermis. It consists of dead cells converted to protein. They are called keratinized cells because they have lost most of their fluid. The organelles of the cell are now just masses of the hard protein keratin that gives this layer its structural strength. These cells are also covered and surrounded with lipids to prevent any passage of fluids through this layer. These cells have only about 20% water as compared to cells in the lowermost layer that have about 70%. The cells resemble scales in shape and can consist of up to 25 layers. By the time cells reach this layer, the desmosomes have broken apart and, therefore, these cells are constantly being sloughed off. The shedding of these cells from the scalp produces what we call dandruff.
This layer also functions as a physical barrier to light and heat waves, microorganisms (e.g., like bacteria, fungi, protozoa and viruses) and most chemicals. The thickness of this layer is determined by the amount of stimulation on the surface by abrasion or weight bearing, hence the thickened palms of the hands and soles of the feet. When skin is subjected to an excessive amount of abrasion or friction, a thickened area called a callus (KAL-us) will develop. Learners who do a lot of writing will develop small calluses on their fingers that hold their pens. Abrasion on the bony prominences on the foot can produce structures we call corns.
The stratum lucidum lies directly beneath the stratum corneum but is difficult to see in thinner skin. It is only one or two cell layers thick. Its cells are transparent and flat.
The stratum granulosum consists of two or three layers of flattened cells. Because granules tend to accumulate in these cells, it was named the granular layer. These granules have nothing to do with skin color. This layer is very active in keratinization. In this layer the cells lose their nuclei and become compact and brittle.
The stratum spinosum consists of several layers of prickly or spiny-shaped cells that are polyhedron in structure. In this layer, desmosomes are still quite prevalent. The outline caused by the polyhedral shapes causes the cell’s outlines to look spiny, hence the name. In some classification schemes, this layer is included with the stratum germinativum.
The stratum germinativum is the deepest and most important layer of the skin because it contains the only cells of the epidermis that are capable of dividing by mitosis. When new cells are formed they undergo morphologic and nuclear changes as they get pushed upward by the dividing cells beneath them. Therefore, these cells give rise to all the other upper layers of the epidermis. The epidermis will regenerate itself only so long as the stratum germinativum remains intact. Its basal layer, called the stratum basale (STRAT-um BAY-sil), rests on the basement membrane.
The stratum germinativum also contains cells called melanocytes (MEL-ah-no-sightz), which are responsible for producing skin color. Melanocytes are irregularly shaped with long processes that extend between the other epithelial cells of this layer. They produce a pigment called melanin (MEL-ah-nin); which is responsible for variations in skin pigmentation. All races have the same number of melanocytes, but the different races have specific genes that determine the amount of melanin produced by the melanocytes. Darker-skinned individuals have more active melanocytes that produce more melanin. Melanocytes are activated to produce melanin by exposure to sunlight. We darken when we expose ourselves to the sun. All races get darker after exposure to the sun over a period of time. We call this getting a suntan.
Based on the discoveries and research done in anthropology by the Leakey family in Olduvai Gorge, Tanzania, scientists believe humans evolved in Africa. The first humanoids were probably very dark to protect themselves from the harmful ultraviolet rays of the sun. They had very active melanocytes like today’s Africans. Over time, some humans migrated away from the equator and genetic recombinations and mutations governing the activity of their melanocytes occurred. Over long periods, this led to the evolution of the different races, whose variations in skin color are determined by the amount of melanin produced and its distribution.
Larger amounts of melanin can occur in certain areas of the body, producing the darkened areola area of the nipples, freckles and moles, although other areas of the body’s skin have less melanin, like the palms of the hands and the soles of the feet. Even though many genes are responsible for skin color, one mutation can cause the absence of skin color by preventing the production of melanin. This condition is called albinism (AL-bih-nizm) and results from a recessive gene that causes the absence of melanin. Albinos have no pigment in their skin and appendages of the skin. Their hair is white, their eyes pink, and their skin very fair. These individuals must be very careful to avoid overexposure to the sun.
The strongest factor in increasing pigmentation in the skin is the sun’s stimulating effect on melanocytes. Melanin cross-links with protein to form a tough resistant compound. Hence, heavily pigmented skin is more resistant to external irritation. People, who live closer to the equator, where there is maximum exposure to sunlight, will be darker than people who live in the north like the Baltic States of Norway, Sweden, Finland and Denmark. This variation in melanin content is the principal factor responsible for the color differences among races. Individuals of darker-skinned races have more active melanocytes, while individuals of lighter-skinned races have less active melanocytes.
The dermis is also known as the corium (KOH-ree-um). It lies directly beneath the epidermis and is often referred to as the true skin. It is composed of dense connective tissue with tough white collagenous fibers and yellow elastin fibers. Blood vessels, nerves, lymph vessels, smooth muscles, sweat glands, hair follicles and sebaceous glands are all embedded in the dermis.
The dermis can be divided into two portions. The papillary portion is the area adjacent to the epidermis, and the reticular portion is found between the papillary portion and the fatty subcutaneous tissue beneath. A sheet of areolar tissue, usually containing fat (adipose tissue), is known as the subcutaneous tissue or superficial fascia and attaches the dermis to underlying structures like muscle or bone. This subcutaneous tissue is sometimes referred to as the hypodermis. It is into this area that hypodermic injections are given. The pink tint of light-skinned individuals is due to blood vessels in the dermis. There are no blood vessels in the epidermis. When an individual is embarrassed, blood vessels in the dermis dilate. This causes “blushing” or the reddish tint seen in the facial area.
When a light-skinned individual suffocates or drowns, carbon dioxide in the blood causes the blood to take on a bluish tinge. This results in the bluish discoloration of skin or cyanosis (sigh-ah-NOH-sis) caused by lack of oxygen in the blood. When a dark-skinned individual suffocates or drowns, the same condition occurs but results in a grayish or ashy tinge to the skin rather than a bluish tinge.
Dead cells converted to protein make up the stratum corneum
A callus on the foot is called a corn
Cells lose their nuclei and become compact and brittle in the stratum granulosum
The stratum spinosum contain cells that are polyhedron in structure.
Cells of the epidermis that are capable of dividing are found in the stratum germinativum
Those cells responsible for skin color are melanocytes
Racial variation in skin color is determined by melanin
True skin is the dermis or corium cyanosis a bluish skin discoloration, is caused by a lack of oxygen in the blood.
The strongest factor in increasing pigmentation in the skin is the stimulating effect of the sun on melanocytes.
When skin is subjected to an excessive amount of abrasion or friction, a thickened area called a callus will develop.
The pigment responsible for variations in skin pigmentation is melanin
The deepest, most important layer of the epidermis containing the only cells capable of dividing by mitosis is the stratum germinativum
The thin, transparent, flat layer that lies directly beneath the outermost layer of the epidermis is the stratum lucidum
Individuals who have no pigment in their skin and its appendages, with resultant white hair, pink eyes, and very fair skin suffer from a condition known as albinism
A burn that completely destroys the epidermis and the dermis and usually requires skin grafts is known as a third-degree burn
The structures associated with the skin include: 1. hair 2. nails 3. sebaceous glands 4. ceruminous glands or wax glands in the ear canal 5. sweat glands
Hair, in addition to mammary glands, is a main characteristic of all mammals. When the hair is very thick and covers most of the surface of the body, as on a dog or cat, it is called fur. Even on humans, hair covers the entire body except the palms of the hands, the soles of the feet and certain portions of the external genitalia (e.g., the head of the penis). In some parts of the body, the hair is so small that it appears invisible, yet in other places it is very obvious as on the head, in the armpits and around the genitalia. The amount of hair a person develops is related to complex genetic factors.
Each individual hair is composed of three parts: 1. the cuticle, 2. the cortex 3. and the medulla.
The outermost portion is the cuticle, which consists of several layers of overlapping scalelike cells. The cortex is the principal portion of the hair. Its cells are elongated and united to form flattened fibers. In people with dark hair, these fibers contain pigment granules. The middle or central part of the hair is called the medulla. It is composed of cells with many sides. These cells frequently contain air spaces. There are other parts to the anatomy of a hair. The shaft is the visible portion of the hair. The root is found in an epidermal tube called the hair follicle. The follicle is made of an outer connective tissue sheath and an inner epithelial membrane continuous with the stratum germinativum.
Attached to the hair follicle is a bundle of smooth muscle fibers that make up the arrector (ah-REK-tohr) pili (PIH-lye) muscle. This muscle causes the goose flesh appearance on our skin when we get scared or when we get a chill. The muscle is involuntary and when it contracts it pulls on the hair follicle, causing the hair to “stand on its end.” We see the goose flesh appearance where hair is scarce. When dogs or cats get angry, their hairs stand up on the nape of their necks. This is all the result of contraction of the arrector pili muscles.
Hair growth is similar to the growth of the epidermis. Note that the hair follicle is an involution of the epidermis. The deeper cell layers at the base of the hair follicle are responsible for the production of new cells by mitosis. The epithelial cells of the hair follicle divide by mitosis and get pushed upward because of the basement membrane. As the cells move upward, they keratinize and form the layers of the hair shaft. Hair growth begins in the hair bulb. Blood vessels in the hair bulb provide the nourishment to produce the hair. Hair grows in cycles.
Hair grows in cycles. The duration of the cycle depends on the hair. Scalp hair grows for 3 years and rests for 1 or 2 years. Hair loss normally means the hair is being replaced because the old hair falls out of the follicle when a new hair begins to form. Some people, particularly men, have a genetic predisposition for what is called pattern baldness. These men suffer a permanent loss of hair because the hair follicles are also lost. This occurs because male sex hormones affect the hair follicles of men with this genetic trait and they become bald.
We classify hair texture as straight, curly or tightly curly (kinky). This is due to genetic factors controlling the nature of the keratin of the hair. The keratin of the cortex of the hair is polymerized and cross-linked chemically in a characteristic folded configuration called alpha keratin, making the fibers elastic. The alpha keratin chain in some individuals produces straight hair, in others curly and in still others tightly curled. When stretched, the keratin chain gets drawn or pulled out into a more linear form called beta keratin. Unless the hair is greatly distended or altered by chemical agents, it will return immediately to its normal alpha configuration. When you wash your hair, it can be elongated to one and one-half its normal length due to the weight of the water on the hair. This is possible because the protein keratin can be readily stretched in the direction of the long axis of the molecular chains of amino acids.
Permanent waves act on this principle and people can change the texture of their hair by going to a beauty salon for treatment. The hair stylist will stretch and mold the hair into the desired new wave: big rollers for straighter hair, small tight rollers for curlier hair. Then a chemical reducing agent is placed on the hair to rupture the old disulfide bonds of the alpha keratin chain. Next a new chemical oxidizing agent is placed on the hair to reestablish new stabilizing cross-links in the new position of the beta chain. Remember, the chemicals only affected the visible portion of the hair or the shaft. The new cells growing from the hair bulb will not have the new texture, and the permanent wave or new style will eventually “grow out.” Another visit to the beauty salon must occur in a few months to redo the process.
Hair color is also determined by complex genetic factors. For example, some people turn gray in their youth, yet others turn gray in their 40s, 50s, or even as late as their 60s. We do know that gray hair occurs when pigment is absent in the cortex of the hair. White hair results from both the absence of pigment in the cortex plus the formation of air bubbles in the shaft.
Hereditary and other unknown factors determine the graying of hair. An interesting research project was done with black cats and gray hair. The hair of a black cat turned gray when its diet was deficient in pantothenic acid (an amino acid). Restoring this substance to its diet caused the gray hair to return to black. Unfortunately, this only works with cats. So the hair coloring industry is still secure.
Great frights, like being in a serious plane or car accident, can cause people’s hair to change color and go gray or white. This occurs quite rarely. We do not know what physiologic processes are triggered that causes this to occur, other than the trauma of such an experience.
At the ends of fingers and toes, we have nails. Other animals have claws (birds, reptiles, cats and dogs) or hooves (horses, cows, deer and elk). The nail is a modification of horny (leathery) epidermal cells composed of very hard keratin. Air mixed in the keratin matrix forms the white crescent at the proximal end of each nail called the lunula (LOO-noo-lah). Again the size of the lunula will vary from person to person and sometimes from nail to nail due to genetic factors. The nail body is the visible part of the nail. The nail root is the part of the nail body attached to the nail bed from which the nail grows approximately 1 mm per week unless inhibited by disease. The cuticle or eponychium is stratum corneum that extends out over the proximal end of the nail body.
Our fingernails grow faster than our toenails. Regeneration of a lost fingernail occurs in 31/2 to 51/2 months. Regeneration of a lost toenail occurs in 6 to 8 months as long as the nail bed remains intact. As we age, the rate of growth of nails slows.
Sebaceous (see-BAY-shus) glands develop along the walls of hair follicles and produce sebum (SEE-bum). This is an oily substance that is responsible for lubricating the surface of our skin, giving it a glossy appearance. Sebaceous secretions consist of entire cells containing the sebum. As the cells disintegrate, the sebum moves along the hair shaft to the surface of the skin where it produces a cosmetic gloss. Brushing hair causes the sebum to cover the shaft of our hair, making hair shiny. Remember how good your dog or cat looks after a good brushing. The coat of fur glistens and shines due to the sebum.
Sebaceous secretion is under the control of the endocrine system. It increases at puberty, resulting in acne problems in adolescents, and it decreases in later life, resulting in dry skin problems. It also increases in late pregnancy.
Sweat glands are simple tubular glands found in most parts of the body. They are not found on the margins of the lips or the head of the penis. They are most numerous in the palms of our hands and in the soles of our feet. It has been estimated that there are 3000 sweat glands per square inch on the palms of our hands. When you get nervous, think about which area of your body gets sweaty first-your hands!
Each sweat gland consists of a secretory portion and an excretory duct. The secretory portion is located in the deep dermis, occasionally in the subcutaneous tissue, and is a blind tube twisted and coiled on itself. A blind tube is one that has only one opening, in this case at the top. From the coiled secretory portion that produces the sweat, the excretory duct spirals up through the dermis into the epidermis and finally opens on the surface of the skin.
Sweat contains the same inorganic materials as blood but in a much lower concentration. Its chief salt is sodium chloride, which is the reason sweat tastes salty. Its organic constituents include urea, uric acid, amino acids, ammonia, sugar, lactic acid and ascorbic acid. Sweat itself is practically odorless. That may surprise you because many of us have been in a locker room at a gym. Actually the odor is produced by the action of bacteria feeding on the sweat. Remember the last time you did some strenuous exercise? You were sweating but there was no odor for the first 10 or 15 minutes. After that time, odor developed because it took that long for the bacterial population to grow in the sweat and their effects to be smelled.
Sweating is also an important physiologic process that cools the body. Sweating leads to loss of heat in the body because heat is required to evaporate the water in sweat. Therefore, sweating helps lower body temperature. Some people are born without sweat glands-they have a congenital absence of these glands. These individuals can easily die of heat stroke if exposed to high temperatures even if only for a brief period of time. Other individuals have overactive sweat glands and must use stronger deodorants and antiperspirants. Due to hair in the armpits, sweat accumulates there. Because our armpits are usually covered while our arms are at our sides, the environment is ideal for bacteria to feed on the sweat, hence the need for deodorants.
Besides mammary glands, hair is a main characteristic of mammals.
Goose bumps are caused by the arrector pili muscle.
Hair growth begins in the hair bulb
A nail will grow from the nail bed
The eponychium is the cuticle
Sebum is the oily substance responsible for lubrication of the skin and is a product of the sebaceous glands
The hands and feet are the site of many sweat glands
Sweating causes odor because of bacterial activity.
Sweat glands are activated by nerves
The most numerous glands in the palms of our hands and the soles of our feet are the sweat glands.
Sweating is an evaporation process that cools the body.
When the arrector pili muscle contracts, it causes the hair to "stand on its end."
The visible part of the fingernail or toenail is known as the nail body
No, because hair grows in a cycle that is shorter than five years.
The epidermis-no nerve endings are in that layer.
Receptor sites in the skin detect changes in the external environment for temperature and pressure. Receptor sites are in contact with sensory neurons that transmit the impulse to the brain and spinal cord for interpretation (see Chapters 10 and 11). Temperature receptors produce the sensations of hot and cold. Pressure receptor sites allow us to interpret excessive pressure that results in the sensation of pain as when we get pinched. They also detect mild pressure that results in the sensation of pleasure as from a gentle massage or a petting stroke. Combinations of varying degrees of those stimulations at these receptor sites produce other sensations that we call burning, itching or tickling. These receptor sites allow us to react to external stimuli and to interpret what is occurring in the outside world.
The skin is an elastic, resistant covering. It prevents passage of harmful physical and chemical agents. The melanin produced by the melanocytes in the stratum germinativum darkens our skin and protects us from the damaging ultraviolet rays of sunlight. Most chemicals cannot gain entry into the body through the skin, but the chemicals that cause poison ivy and poison oak can penetrate this barrier. Fat-soluble chemicals like DDT, a chlorinated hydrocarbon pesticide, can also get through the skin. If you put your hand in a can of gasoline, you will not be poisoned. However, if you put your hand in a can of DDT, you could be poisoned. People who work with certain insecticides must wear protective clothing to prevent the penetration of these chemicals through their skin.
The lipid content of the skin inhibits the excessive loss of water and electrolytes through the skin. Normal skin is impermeable to water, carbohydrates, fat and protein. However, all true gases and certain volatile substances will pass through the epidermis like the organic pesticide just mentioned. The numerous openings around hair follicles can act as channels for absorption of these materials.
Skin also has an “acid mantle.” This acidity kills most bacteria and other microorganisms that make contact with our skin. Soaps and shampoos will often be labeled as pH balanced, which indicates that these cleansers will not destroy the acid mantle of the skin. Some skin diseases will destroy the acidity of certain areas of the skin, impairing the self-sterilizing capabilities of our skin. These diseases make the skin prone to bacterial infections.
Nails protect the ends of our digits. Fingernails can also be used in defense. Hair on our head acts as an insulator and helps prevent heat loss. Hairs in our nose filter out large foreign particles like soot. Eyelashes protect our eyes from foreign objects.
Normal body temperature is maintained at approximately 98.6°F (37°C). Temperature regulation is critical to our survival because changes in temperature affect the functioning of enzymes. The presence of enzymes is critical for normal chemical reactions to occur in our cells. When people get high fevers, they can die because the heat of a fever destroys the enzymes by breaking up their chemical structure. Without enzymes, chemical reactions cannot occur and our cellular machinery breaks down and death results.
When external temperatures increase; blood vessels in the dermis dilate to bring more blood flow to the surface of the body from deeper tissue beneath. In the skin the blood with its temperature or heat is then lost by radiation, convection, conduction and evaporation. When we sweat, the water in sweat evaporates which requires energy and thus carries away heat to reduce body temperature.
When external temperatures decrease, the first response is for blood vessels in the dermis to dilate to bring heat to the surface to warm our extremities. Light-skinned individuals will have rosy cheeks when they first go out during a cold wintry day. Excessive exposure to the cold cannot be maintained for long, so blood vessels then constrict to bring the heat inside to preserve the vital organs of the body. Frostbite occurs when the skin of the extremities no longer gets a blood supply due to the maintained constriction of the blood vessels in the dermis to conserve heat. The tissues in the tips of these extremities die and turn black.
The skin produces two secretions: sebum and sweat. Sebum is secreted by the sebaceous glands. In addition to imparting a cosmetic gloss to our skin and moisturizing our skin, sebum has both antifungal and antibacterial properties. It helps prevent infection and maintains the texture and integrity of the skin. Sweat is produced by the sweat glands and is essential in the cooling process of the body. Sweat also contains waste products such as urea, ammonia and uric acid and so can also be considered an excretion. A secretion is something beneficial; whereas an excretion is something the body does not need and could be harmful.
The skin is actively involved in the production of vitamin D. Exposure to the ultraviolet rays of the sun stimulates our skin to produce a precursor molecule of vitamin D that then goes to the liver and kidneys to become mature vitamin D. Vitamin D is necessary for our bodies because it stimulates the intake of calcium and phosphorus in our intestines. Calcium is necessary for muscle contraction and bone development. Phosphorus is an essential part of adenosine triphosphate. Because we live indoors, and in colder climates wear heavy clothing, we sometimes do not get enough exposure to the sun to adequately produce enough vitamin D. We also should ingest vitamin D through our diets. Good sources of vitamin D are milk and fish oils.
Sensations recorded by the skin are temperature and pressure
Inhibition of water loss by the skin is due to its lipid content.
Body Systems Working Together to Maintain Homeostasis: The Integumentary System Skeletal System | |

Vitamin D manufactured by the skin helps provide calcium for strong bones. | |

Muscular System 1. Vitamin D helps provide calcium for muscle contraction. 2. Facial muscles produce facial expressions of body language. 3. Shivering helps control body temperature by warming the body. | |

Nervous System 1. Receptor sites for temperature and pressure changes in the skin provide information to the nervous system so we can cope with our external environment. 2. Nerves activate sweat glands. | |

Endocrine System 1. Hormones control the secretion of sebum from the sebaceous glands. 2. Hormones increase blood flow to the skin. 3. Hormones control the amount of fat in subcutaneous tissue. | |

Cardiovascular System 1. Blood vessels in the dermis help regulate body temperature by dilating or constricting. 2. Dilation of blood vessels in light skin produces blushing during embarrassing moments. | |

Lymphatic System 1. Skin is an effective barrier against invasion by microorganisms providing a first defense for the immune system. 2. Sebum has antifungal and antibacterial properties. 3. The acid mantle of the skin helps prevent most bacterial infections. | |

Digestive System 1. Vitamin D produced by the skin causes calcium and phosphorus to be absorbed in the intestine. 2. Excess calories can be stored as fat in subcutaneous tissue. | |

Respiratory System 1. Receptor sites in the skin can bring about changes in breathing rates. | |

Urinary System 1. Kidneys can restore water and electrolytes lost during sweating. | |

Reproductive System 1. Stimulation of receptor sites in the skin can bring about sexual interest. 2. Sucking on the nipple causes the postnatal female to produce milk from her mammary glands. |
CHAPTER 7
The skeletal system includes all the bones of the body and their associated cartilage, tendons and ligaments. Despite the appearance of the bones, they are indeed composed of living tissue. The hard, “dead” stonelike appearance of bones is due to mineral salts like calcium phosphate embedded in the inorganic matrix of the bone tissue.
Leondardo da Vinci (1452-1519), the famous Italian Renaissance artist and scientist, is credited as the first anatomist to correctly illustrate the skeleton with its 206 bones.
The skeleton has five general functions: 1. Support 2. Movement 3. Protection 4. Mineral Storage 5. Blood Cell Formation
It supports and stabilizes surrounding tissues such as muscles, blood vessels, nerves, fat and skin.
It assists in body movement by providing attachments for muscles that pull on the bones that act as levers.
It protects vital organs of the body such as the brain, spinal cord, the heart and lungs, and it protects other soft tissues of the body.
It is a storage area for mineral salts, especially phosphorus and calcium, and fats.
It manufactures blood cells. This process is called hematopoiesis (hem-ah-toh-poy-EE-sis) and occurs chiefly in red bone marrow.
Associated with the bones are: 1. cartilage 2. tendons 3. ligaments
Associated with the bones are: 1. cartilage 2. tendons 3. ligaments
Ligaments are tough connective tissue structures that attach bones to bones like the ligament that attaches the head of the femur to the acetabulum of the pelvic bone in the hip joint.
Tendons are similar structures that attach muscle to bone.
Next, let's take a look at how the skeleton system works together with other body systems to maintain homeostasis.
Integumentary System 1. Vitamin D is produced in the skin by UV light. 2. It enhances the absorption of calcium in bones for bone and tooth formation.

Muscular System
Through their tendons, muscles pull on bones, bringing about movement.
Calcium from bones is necessary for muscle contraction to occur.
Nervous System 1. The cranial bones protect the brain, and the vertebrae and intervertebral disks protect the spinal cord. 2. Receptors for pain monitor trauma to bones. 3. Calcium from bones is necessary for nerve transmission.

Endocrine System 1. The hormone calcitonin causes calcium to be stored in bones. 2. The hormone parathormone causes calcium to be released from bones. 3. Growth hormone from the anterior pituitary gland effects bone development.

Cardiovascular System 1. Blood cells transport oxygen and nutrients to bone cells and take away carbon dioxide and waste products. 2. Calcium from bones is necessary for blood clotting and normal heart functions.

Lymphatic System 1. Red bone marrow produces lymphocytes, which function in our immune response.

Digestive System 1. Calcium, necessary for bone matrix development, is absorbed in the intestine from our daily food intake. 2. Excess calcium can be eliminated via the bowels.

Respiratory System 1. Oxygen is brought into the body via the respiratory system and transported by the blood to bone cells for biochemical respiration. 2. The ribs along with the intercostal muscles and diaphragm bring about breathing.

Urinary System 1. The kidneys help regulate blood calcium levels. 2. Excess calcium can also be eliminated via the kidneys.

Reproductive System 1. Bones are a source of calcium during breastfeeding. 2. The pelvis aids in supporting the uterus and developing fetus during pregnancy in the female.
The skeletal system has 5 general functions.
The function of the red bone marrow is the formation of red and white blood cells and blood platelets, a process known as: hematopoiesis
The skeleton of a developing fetus is completely formed by the end of the third month of pregnancy. However, at this time, the skeleton is predominantly cartilage. During the subsequent months of pregnancy, ossification, the formation of bone, and growth occur. The osteoblasts invade the cartilage and begin the process of ossification. Longitudinal growth of bones continues until approximately 15 years of age in girls and 16 years of age in boys. This takes place at the epiphyseal line or plate. Bone maturation and remodeling continue until the age of 21 in both sexes. It would be incorrect to state that cartilage actually turns into bone. Rather cartilage is the environment in which the bone develops.

The strong protein matrix is responsible for a bone’s resilience or “elasticity” when tension is applied to the bone so that it gives a little under pressure. The mineral salts deposited into this protein matrix are responsible for the strength of the bone so that it does not get crushed when pressure is applied to the bone.
Deposition of Bone | Bone develops from spindle-shaped cells called osteoblasts that develop from undifferentiated bone cells called osteoprogenitor (oss-tee-oh-pro-JEN-ih-tohr) cells. These osteoblasts are formed beneath the fibrovascular membrane that covers a bone called the periosteum (pair-ee-AH-stee-um). These osteoblasts are also found in the endosteum (en-DOS-tee-um), which lines the bone marrow or medullary cavity. |
Deposition of bone is controlled by the amount of strain or pressure on the bone. The more strain, the greater the deposition of bone. The heel bone, or calcaneum, is a large strong bone because it receives the weight of the body when walking. Bones (and muscles) in casts will waste away or atrophy, whereas continued and excessive strain via exercise will cause the bone and muscles to grow thick and strong. This is the reason children are told to run and play to develop strong bones during their formative years. When a cast is removed, the patient participates in physical therapy to build up the bone (and muscles) that became weak while in the cast.
A break in a bone will stimulate injured osteocytes to proliferate. They then secrete large quantities of matrix to form new bone. In addition, other types of bone cells called osteoclasts are present in almost all cavities of bone. They are derived from immune system cells and are responsible for the reabsorption of bone. These are large cells that remove bone from the inner side during remodeling, such as when a bone is broken.
Osteoclasts are also responsible for the ability of a crooked bone to become straight. If a young child is detected to be bow-legged, the physician will apply braces to the legs. Periodic tightening of the braces puts pressure on the bone so that new bone is deposited by osteocytes (mature osteoblasts), or mature bone cells, while the osteoclasts remove the old bone during this remodeling process. This process can cause a broken bone that was set improperly to heal incorrectly. To correct this, the bone must be broken again and correctly reset to straighten properly.
There are two types of ossification (oss-sih-fih-KAY-shun) (the formation of bone by osteoblasts). Both types of ossification result in compact and cancellous bone: 1. Intramembranous Ossification 2. Endochondral Ossification
The first type is intramembranous ossification, in which dense connective tissue membranes are replaced by deposits of inorganic calcium salts, thus forming bone. The membrane itself will eventually become the periosteum of the mature bone. Underneath the periosteum will be compact bone with an inner core of spongy or cancellous bone. Only the bones of the cranium or skull form by this process. Because complete ossification in this way does not occur until a few months after birth, one can feel these membranes on the top of a baby’s skull as the soft spot or fontanelle (fon-tah-NELL). This allows the baby’s skull to give slightly as it moves through the birth canal.
Endochondral Ossification | The other bones of the body are formed by the second process called endochondral (en-doh-KON-dral) ossification. This is the process in which cartilage is the environment in which the bone cells develop (endo = inside, chondro = cartilage). As the organic matrix becomes synthesized, the osteoblast becomes completely surrounded by the bone matrix and the osteoblast becomes a mature bone cell or osteocyte. |
In a healthy body, a balance must exist between the amount of calcium stored in the bones, the calcium in the blood and the excess calcium excreted by the kidneys and via the digestive system. The proper calcium ion concentration in the blood and bones is controlled by the endocrine system. Two hormones, calcitonin and parathormone, control the calcium concentration in our bodies. Calcitonin causes calcium to be stored in the bones; parathormone causes it to be released into the bloodstream.
Osteoblasts invade cartilage and begin the process of ossification.
The endosteum is the membrane that lines the medullary cavity.
Bone remodeling is made possible by osteocytes and osteoclasts.
Correct calcium ion concentration in blood and bone is maintained by calcitonin, which stores calcium, and parathormone, which releases it.
Osteoclasts are large cells that are present in the cavities of bone that function in the reabsorption of bone.
The replacement of cartilaginous structures with bone is called: endochondral ossification
The fibrovascular membrane that covers a bone is called the: periosteum
Large cells that are present in the cavities of bone that function in the reabsorption of bone are known as: osteoclasts
There are two types of bone tissue: compact or dense bone, and cancellous or spongy bone. In both types of tissue, the osteocytes are the same, but the arrangement of how the blood supply reaches the bone cells is different. The two types of tissue have different functions. Compact bone is dense and strong, whereas cancellous bone has many open spaces, giving it a spongy appearance. It is in these spaces that bone marrow can be found.
The haversian (hah-VER-shan) canal, also called an osteon, was named for an English physician, Clopton Havers (1650-1702), who first described it as a prominent feature of compact bone. This system allows for the effective metabolism of bone cells surrounded by rings of mineral salts.
It has several components. Running parallel to the surface of the bone are many small canals containing blood vessels (capillaries, arterioles, venules) that bring in oxygen and nutrients and remove waste products and carbon dioxide. These canals are called haversian or central canals and are surrounded by concentric rings of bone, each layer of which is called a lamella (lah-MELL-ah). Between two lamellae or rings of bone are several tiny cavities called lacunae (lah-KOO-nee). Each lacuna contains an osteocyte or bone cell suspended in tissue fluid. The lacunae are all connected to each other and ultimately to the larger haversian canals by much smaller canals called canaliculi (kan-ah-LIK-you-lye).
Canals running horizontally to the haversian (central) canals, also containing blood vessels, are called Volkmann’s or perforating canals. It is tissue fluid that circulates through all these canals and bathes the osteocyte, bringing in oxygen and food and carrying away waste products and carbon dioxide, keeping the osteocytes alive and healthy.
Cancellous or spongy bone is located at the ends of long bones and forms the center of all other bones. It consists of a meshwork of interconnecting sections of bone called trabeculae (trah-BEK-you-lee), creating the spongelike appearance of cancellous bone. The trabeculae give strength to the bone without the added weight of being solid. Each trabecula consists of several lamellae with osteocytes between the lamellae just as in compact bone. The spaces between the trabeculae are filled with bone marrow. Nutrients exit blood vessels in the marrow and pass by diffusion through the canaliculi of the lamellae to the osteocytes in the lacunae.
There are two types of bone marrow: 1. Red Bone Marrow 2. Yellow Bone Marrow

The many spaces within cancellous bone are filled with red bone marrow. This marrow is richly supplied with blood and consists of blood cells and their precursors. The function of red bone marrow is hematopoiesis, or the formation of red and white blood cells and blood platelets. Therefore, blood cells in all stages of development will be found in red bone marrow. We shall discuss in more detail the different stages of blood cell development in Chapter 13.
In an adult, the ribs, vertebrae, sternum and bones of the pelvis all contain red bone marrow in their cancellous tissue. These bones produce blood cells in adults. Red bone marrow within the ends of the humerus or upper arm and the femur or thigh is plentiful at birth but gradually decreases in amount as we age.
Yellow bone marrow is connective tissue consisting chiefly of fat cells. It is found primarily in the shafts of long bones within the medullary cavity, the central area of the bone shaft. Yellow bone marrow extends into the osteons or haversian systems, replacing red bone marrow when it becomes depleted.
Compact bone is dense and strong, whereas cancellous bone is spongy.
An osteon, also called the haversian canal, allows for the effective metabolism of bone cells.
The spaces within cancellous bone contain red bone marrow, which are responsible for hematopoiesis.
Delsin is studying his little brother’s ant colony. He notices some canals that run horizontally, connecting larger tubes. Those canals reminded him of Volkmann’s canals in compact bone that connect osteons.
The individual bones of the body can be divided by shape into five categories: long, short, flat, irregular and sesamoid.
Long bones are bones whose length exceeds their width and consist of a diaphysis (dye-AFF-ih-sis) or shaft composed mainly of compact bone, a metaphysis (meh-TAFF-ih-sis) or flared portion at each end of the diaphysis consisting mainly of cancellous or spongy bone, and two extremities, each called an epiphysis (eh-PIFF-ih-sis), separated from the metaphysis by the epiphyseal line where longitudinal growth of the bone occurs.
The shaft consists mainly of compact bone. It is thickest toward the middle of the bone because strain on the bone is greatest at that point. The strength of a long bone is also ensured by the slight curvature of the shaft, a good engineering design to distribute weight.

The interior of the shaft is the medullary cavity filled with yellow bone marrow. The extremities or the epiphyses of the long bone have a thin covering of compact tissue overlying a majority of cancellous tissue, which usually contains red marrow.
The extremities or the epiphyses of the long bone have a thin covering of compact tissue overlying a majority of cancellous tissue, which usually contains red marrow. The epiphyses are usually broad and expanded for articulation with other bones and to provide a large surface for muscle attachment.
Examples of obvious long bones are the clavicle, humerus, radius, ulna, femur, tibia and fibula. Not so obvious are those short versions of a long bone, the metacarpals of the hand, the metatarsals of the foot and the phalanges of the fingers and toes.

Short bones are not merely shorter versions of long bones. They lack a long axis. They have a somewhat irregular shape. They consist of a thin layer of compact tissue over a majority of spongy or cancellous bone. Examples of short bones of the body are the carpal bones of the wrist and the tarsal bones of the foot.
Flat bones are thin bones found whenever there is a need for extensive muscle attachment or protection for soft or vital parts of the body. These bones, usually curved, consist of two flat plates of compact bone tissue enclosing a layer of cancellous bones. Examples of flat bones are the sternum, ribs, scapula, parts of the pelvic bones and some of the bones of the skull.
Irregular bones are bones of a very peculiar and different or irregular shape. They consist of spongy bone enclosed by thin layers of compact bone. Examples of irregular bones are the vertebrae and the ossicles of the ears.
Sesamoid (SESS-ah-moyd) bones are small rounded bones. These bones are enclosed in a tendon and fascial tissue and are located adjacent to joints. They assist in the functioning of muscles. The kneecap, or patella, is the largest of the sesamoid bones. Some of the bones of the wrist and ankle could also be classified as sesamoid bones as well as short bones.
Long bones consist of a diaphysis (or shaft), metaphysis (or flared portion) and a(n) epiphysis (or extremity).
Sesamoid bones are enclosed in a tendon and fascial tissue.
The largest of the sesamoid bones is the patella, commonly known as: the kneecap.
The surface of any typical bone will exhibit certain projections called processes or certain depressions called fossae (FOSS-ee), or both. These markings are functional in that they can help join one bone to another, provide a surface for the attachments of muscles, or serve as a passageway into the bone for blood vessels and nerves. The following is a list of terms and definitions regarding bone markings.
Processes is a general term referring to any obvious bony prominence. The following is a list of specific examples of processes. 1. Spine 2. Condyle 3. Tubercle 4. Trochlea 5. Trochanter 6. Crest 7. Line 8. Head 9. Neck

Spine: any sharp, slender projection such as the spinous process of a vertebra.

Condyle (KON-dial): a rounded or knuckle-like prominence usually found at the point of articulation with another bone such as the lateral and medial condyle of the femur.
Tubercle (TOO-ber-kl): a small round process like the lesser tubercle of the humerus.
Trochlea (TROK-lee-ah): a process shaped like a pulley as in the trochlea of the humerus.
Trochanter (tro-KAN-ter): a very large projection like the greater and lesser trochanter of the femur.
Crest: a narrow ridge of bone like the iliac crest of the hip bone.
Line: a less prominent ridge of bone than a crest.
Head: a terminal enlargement like the head of the humerus and the head of the femur.
Neck: that part of a bone that connects the head or terminal enlargement to the rest of the bone, like the neck of the femur.

Fossae is a general term for any depression or cavity in or on a bone. The following is a list of specific examples of fossae. 1. Suture 2. Foramen 3. Meatus or canal 4. Sinus or antrum 5. Sulcus
Suture: a narrow junction often found between two bones like the sutures of the skull bones.
Foramen: an opening through which blood vessels, nerves and ligaments pass like the foramen magnum of the occipital bone of the skull or the obturator foramen of the pelvic bone.
Meatus or canal: a long tube-like passage, like the auditory meatus or canal.

Sinus or antrum: a cavity within a bone like the nasal sinuses or frontal sinus (see).
Sulcus: a furrow or groove like the intertubercular sulcus or groove of the humerus.
An obvious bony prominence is called a(an) process.
A depression or cavity in or on a bone is called a(an) fossae.
The skeleton typically has 206 named bones. The axial part consists of the skull (28 bones, including the cranial and facial bones), the hyoid bone, the vertebrae (26 bones), the ribs (24 bones) and the sternum. The appendicular part of the skeleton consists of the bones of the upper extremities or arms (64 bones, including the shoulder girdle bones) and the bones of the lower extremities or legs (62 bones, including the bones of the pelvic girdle).
The skull, in the correct use of the term, includes the cranial and the facial bones. We will discuss the cranial bones first.
When learning the different bones of the skull, one of the best methods is to first refer to the full color figures of the cranial and facial bones where each individual bone is portrayed in a different color. Refer to the figures on the left for the anterior view of the skull, and the lateral view of the skull. Once you get a sense of where these bones are located, use a model of a human skull (either real bone or a good plastic reproduction) and search for sutures as a guide. Remember that in a real skull the older the skull, the less obvious the sutures become. As we age, the sutures tend to disappear or become very faint. The full color figures will greatly assist you in learning where the bones of the skull are found.
The bones of the cranium have a number of important functions. They protect and enclose the brain and special sense organs like the eyes and ears. Muscles for mastication or chewing and muscles for head movement attach to certain cranial bones. At certain locations, air sinuses or cavities are present that connect with the nasal cavities. All of the individual bones of the cranium are united by immovable junction lines called sutures.
The frontal bone is a single bone that forms the forehead, the roof of the nasal cavity and the orbits, which are the bony sockets that contain the eyes. Important bone markings are the orbital margin, a definite ridge above each orbit located where eyebrows are found, and the supraorbital ridge, which overlies the frontal sinus and can be felt in the middle of your forehead. The coronal suture is found where the frontal bone joins the two parietal bones.
The two parietal (pah-RYE-eh-tal) bones form the upper sides and roof of the cranium. They are joined at the sagittal suture in the midline.
The occipital bone is a single bone that forms the back and base of the cranium and joins the parietal bones superiorly at the lambdoid suture. The inferior portion of this bone has a large opening called the foramen magnum through which the spinal cord connects with the brain. On each lower side of the occipital bone is a process called the occipital condyle. These processes are significant because they articulate with depressions in the first cervical vertebra (atlas), thus allowing the head to connect with and rest on the vertebrae. Other notable markings are the external occipital crest and the external occipital protuberance, which can be felt through the scalp at the base of the neck. Several ligaments and muscles attach to these regions.
The two temporal bones help form the lower sides and base of the cranium. Each temporal bone encloses an ear and bears a fossa for articulation with the lower jaw or mandible. The temporal bones are irregular in shape and each consists of four parts: the squamous, petrous, mastoid and tympanic parts.
The squamous portion is the largest and most superior of the four parts. It is a thin flat plate of bone that forms the temple. Projecting from its lower part is the zygomatic process that forms the lateral part of the zygomatic arch or cheek bone.
The petrous part is found deep within the base of the skull where it protects and surrounds the inner ear.
The mastoid portion is located behind and below the auditory meatus or opening of the ear. The mastoid process is a rounded projection of the mastoid portion of the temporal bone easily felt behind the ear. Several muscles of the neck attach to this mastoid process and assist in moving your head.
Finally, the tympanic plate forms the floor and anterior wall of the external auditory meatus. A long and slender styloid process can be seen extending from the under surface of this plate. Ligaments that hold the hyoid bone in place (which supports the tongue) attach to this styloid process of the tympanic plate of the temporal bone.

The single sphenoid bone forms the anterior portion of the base of the cranium. When viewed from below it looks like a butterfly. It acts as an anchor binding all of the cranial bones together.
The single ethmoid bone is the principal supporting structure of the nasal cavities and helps form part of the orbits. It is the lightest of the cranial bones.

The six auditory ossicles are the three bones found in each ear (see Figure 7-7B): the malleus or hammer, the stapes (STAY-peez) or stirrup and the incus or anvil. These tiny bones are highly specialized in both structure and function and are involved in exciting the hearing receptors.
The wormian bones or sutural bones are located within the sutures of the cranial bones. They vary in number, are small and irregular in shape and are never included in the total number of bones in the body. They form as a result of intramembranous ossification of the cranial bones.
Like the bones of the cranium, the facial bones are also united by immovable sutures, with one exception: the lower jawbone or mandible. This bone is capable of movement in a number of directions. It can be elevated and depressed as in talking, and it can protract and retract and move from side to side as in chewing.
The two nasal bones are thin and delicate bones that join in a suture to form the bridge of the nose.
The two palatine bones form the posterior part of the roof of your mouth or part of the hard palate. This region is the same as the floor of the nasal cavity. Upward extensions of the palatine bones help form the outer walls of the nasal cavity.
The two maxillary bones make up the upper jaw. Each maxillary bone consists of five parts: a body, a zygomatic process, a frontal process, a palatine process and an alveolar process. The two maxillary bones join at the intermaxillary suture. This fusion is usually completed just before birth. If the two bones do not unite to form a continuous structure, the resulting defect is called a cleft palate and is usually associated with a cleft lip. With today’s surgical techniques, the defect can be repaired early in the development of the child.
The large body of the maxilla forms part of the floor and outer wall of the nasal cavity, the greater part of the floor of the orbit and much of the anterior face below the temple. The body is covered by a number of facial muscles and contains a large maxillary sinus located lateral to the nose.
The zygomatic process extends laterally to participate in the formation of the cheek. (Processes are named according to the bone they go to; thus, the zygomatic process of the maxillary bone goes toward and joins the zygomatic or cheekbone.)
The frontal process extends upward to the frontal bone or forehead. The palatine process extends posteriorly in a horizontal plane to join or articulate with the palatine bone and actually forms the greater anterior portion of the hard palate or roof of the mouth.
The alveolar processes bear the teeth of the upper jaw, and each tooth is embedded in an alveolus (al-VEE-oh-lus) or socket.
The two zygomatic bones, also known as the malar bones, form the prominence of the cheek and rest on the maxillae. Its maxillary process joins the maxillary bone by connecting with the maxillary bone’s zygomatic process. Each zygomatic bone has a frontal process extending upward to articulate with the frontal bone and a smaller temporal process that joins laterally with the temporal bone, thus forming the easily identified zygomatic arch.
The two lacrimal (LAK-rim-al) bones make up part of the orbit at the inner angle of the eye. These very small and thin bones lie directly behind the frontal process of the maxilla. Their lateral surface has a depression or fossa that holds the lacrimal sac or tear sac and provides a canal for the lacrimal duct. Tears are directed from this point to the inferior meatus of the nasal cavity after they have cleansed and lubricated the eye.
The two turbinates or nasal conchae bones are very thin and fragile. There is one in each nostril on the lateral side. They extend to but do not quite reach the bony portion of the nasal septum. They help form a series of shelves in the nasal cavity where air is moistened, warmed and filtered.
The single vomer bone is a flat bone that makes up the lower posterior portion of the nasal septum.
The single mandible bone develops in two parts. The intervening cartilage ossifies in early childhood, and the bone becomes fused into a single continuous structure. It is the strongest and longest bone of the face. It consists of a U-shaped body with alveolar processes to bear the teeth of the lower jaw (just like the maxillary bone’s alveolar processes that bear the teeth of the upper jaw). On each side of the body are the rami that extend perpendicularly upward. Each ramus has a condyle for articulation with the mandibular fossa of the temporal bone, thus allowing for the wide range of movement of the lower jawbone.
Other bones also include: 1. The orbits 2. Nasal cavities 3. Foramina of the Skull 4. Hyoid Bone
The orbits are the two deep cavities in the upper portion of the face that protect the eyes. A number of bones of the skull contribute to their formation. Refer to the figure on the right previous page to view these bones. Each orbit consists of the following bones:

The framework of the nose surrounding the two nasal fossae is located in the middle of the face between the hard palate inferiorly and the frontal bone superiorly.

If one views the skull inferiorly and observes the floor of the cranial cavity, one can observe the largest foramen of the skull, the foramen magnum. One can also observe a number of much smaller foramina or openings that penetrate the individual bones of the skull. They all have names and are passageways for blood vessels and nerves entering and exiting the various organs of the skull.

The single hyoid bone is a unique component of the axial skeleton because it has no articulations with other bones. It is rarely seen as part of an articulated skeleton in a lab. Rather, it is suspended from the styloid process of the temporal bone by two styloid ligaments. Externally, you can detect its position in the neck just above the larynx or voice box a fair distance from the mandible. It is shaped like a horseshoe consisting of a central body with two lateral projections. The larger projections are the greater cornu, and the smaller lateral projections are the lesser cornu. The hyoid bone acts as a support for the tongue and its associated muscles. It also helps elevate the larynx during swallowing and speech.
The sternum, ribs and vertebrae make up the trunk or torso of the axial skeleton. The vertebrae are rigid and provide support for the body but the fibrocartilaginous disks between the vertebrae allow for a high degree of flexibility. The disks and vertebrae protect the delicate spinal cord contained within their articulated channels formed from successive foramina. The spinal column is formed from a series of 26 irregular bones called vertebrae, separated and cushioned by the intervertebral disks of cartilage. |

| Refer to the figure on the right for views of the structure of the vertebral column. There are 7 cervical vertebrae, 12 thoracic vertebrae and 5 lumbar vertebrae. These all remain separate throughout life and are referred to as movable. In addition there are five sacral vertebrae that become fused by adult life and form the single sacrum. There are also four coccygeal vertebrae that unite firmly to form the single coccyx or tailbone. These last two, the sacrum and coccyx, are called fixed, hence the vertebrae are referred to in number as 26 rather than 33. | | A typical vertebra has the following parts or features: |

| The body |

| The neural arch |

| The articular processes |

| The vertebral arch | | The body is a thick disk-shaped anterior portion pierced with numerous small holes for nerves and blood vessels that nurture the bone. |

| The neural arch encloses a space, the neural foramen, for passage of the spinal cord. The arch has three processes for muscle attachment: the spinous process, quite large on the thoracic vertebrae, directed backward, and two transverse processes, one on each side of the vertebra. | The articular processes are used for articulating with the vertebra immediately above by the two superior articular processes and with the vertebra immediately below by the two inferior articular processes. |

| The vertebral arch is composed of two portions on each side, the pedicles notched above and below for passage of nerves to and from the spinal cord, and the laminae, which form the posterior wall of the vertebral column.There are 7 cervical vertebrae, 12 thoracic vertebrae and 5 lumbar vertebrae. These all remain separate throughout life and are referred to as movable. In addition there are five sacral vertebrae that become fused by adult life and form the single sacrum. There are also four coccygeal vertebrae that unite firmly to form the single coccyx or tailbone. These last two, the sacrum and coccyx, are called fixed, hence the vertebrae are referred to in number as 26 rather than 33.The cervical vertebrae are the smallest vertebrae. The first two have been given special names . The first is called the atlas (named after Atlas in Greek mythology who held up the world); it supports the head by articulation with the condyles of the occipital bone.The second vertebra is the axis; it acts as the pivot on which the atlas and head rotate. The thoracic vertebrae have two distinguishing characteristics: the long spinous process pointing downward and six facets, three on each side for articulation with a rib.
The lumbar vertebrae are the largest and the strongest. They are modified for the attachment of the powerful back muscles.The sacrum is a triangular and slightly curved bone. The curving coccyx can move slightly to increase the size of the birth canal during delivery in the female.In addition to providing protection for the spinal cord and support for the body, the vertebral column is also built to withstand forces of compression many times the weight of the body. The fibrocartilaginous intervertebral disks act as cushions so that landing on your feet after a jump or a fall will help prevent the vertebrae from fracturing.The thorax or the rib cage of the body is made up of the sternum, the costal cartilages, the ribs and the bodies of the thoracic vertebrae. This bony cage encloses and protects the heart and lungs. It also supports the bones of the shoulder girdle and the bones of the upper extremities.
The sternum is also known as the breastbone. It develops in three parts: the manubrium, the gladiolus and the xiphoid (ZIFF-oyd) process. The sternum resembles a sword, with the manubrium resembling the handle of the sword, the gladiolus or body forming the blade and the xiphoid process forming the tip of the sword. No ribs are attached to the xiphoid, but the manubrium and gladiolus have notches on each side for attachment of the first seven costal (rib) cartilages. The manubrium articulates with the clavicle or collarbone. Between these two points of attachment is the suprasternal or jugular notch easily felt through the skin. The diaphragm and the rectus abdominis muscles attach to the xiphoid.The 12 pairs of ribs are also referred to as the costae. They are named according to their anterior attachments. Because the upper seven pairs articulate directly with the sternum, they are called true ribs. The lower five pairs are called false ribs. The costal cartilages of the 8th, 9th, and 10th rib pairs are attached to the cartilage of the 7th rib so they join the sternum only indirectly. Because the 11th and 12th pairs of ribs have no cartilage and do not attach at all anteriorly, these “false” ribs have another name, floating ribs. Of course, all ribs attach posteriorly to the thoracic vertebrae. |
The skeleton is divided into two main parts, the appendicular (which consists of the extremities) and the axial.
The occipital bone is a single bone that forms the posterior base of the cranium.
The anchor bone for the cranium is the single sphenoid bone.
The freely movable bone of the face is the mandible bone.
The spinal cord passes through a space called the neural foramen.
The largest and strongest vertebrae are those of the lumbar section of the spine.
The frontal bone forms the forehead, the roof of the nasal cavity, and the orbits.
The single bone that forms the forehead, the roof of the nasal cavity, and the orbits, which are the bony sockets that contain the eyes, is the: frontal bone
The two very small, thin bones that make up part of the orbit at the inner angle of the eye are the: lacrimal bones
The first cervical vertebra, which supports the head, is called: atlas
The only bone in the body that does not articulate with any other bones but is suspended by ligaments from the styloid process of the temporal bone is the: hyoid bone
When the palatine processes of the maxillary bones do not fuse properly, resulting in an opening between the oral and nasal cavities, the condition is known as: cleft palate
Winnie the Pooh sat on a log, tapping his forehead trying to remember where his honey had disappeared. What bone was he tapping? frontal bone
The upper extremities include the bones of the: 1. shoulder girdle 2. arm 3. forearm 4. wrist 5. hand 6. fingers
The bones of the shoulder girdle are the clavicle (KLAV-ih-kl) and the scapula (SKAP-you-lah). The clavicle or collarbone is a long slim bone located at the root of the neck just below the skin and anterior to the first rib. The medial end articulates with the manubrium of the sternum and the lateral end with the acromial (ah-KRO-mee-al) process of the scapula. The scapula or shoulder blade is a large, flat, triangular bone located on the dorsal portion of the thorax, covering the area from the second to the seventh rib. Two other prominent bony projections on the scapula are the coracoid process, which functions as an attachment for muscles that move the arm, and the glenoid fossa, which receives the head of the humerus and helps form the shoulder joint.
The humerus (HYOO-mehr-us) is the largest and longest bone of the upper arm. Its head is rounded and joined to the rest of the bone by its anatomic neck. The upper part of the bone has two prominences, the greater and lesser tubercles, which function as insertions for many of the muscles of the upper extremity. The ulna is the longer, medial bone of the forearm. Its shaft is triangular, and the distal, or lower, end is called the head. At its proximal end is the olecranon (oh-LEK-rah-non) process or elbow. When banged, nerves are pressed causing the tingling sensation, which gives it the common name of “funny bone.” |

| The radius is the shorter, lateral bone of the forearm. It is joined to the ulna by an interosseus membrane traversing the area between the shafts of the two bones. They move as one. The styloid process of the radius articulates with some of the bones of the wrist. |

The bones of the wrist are called carpals. They are arranged in two rows of four each. In the proximal row from medial to lateral they are the pisiform (PYE-zih-form), triquetral (try-KWEE-tral), lunate (LOO-nate) and scaphoid (SKAFF-oyd), also known as the navicular (nah-VIK-you-lahr). In the distal row from medial to lateral are the hamate, capitate (KAP-ih-tate), trapezoid (TRAP-eh-zoyd), or lesser multiangular, and the trapezuim (trah-PEE-zee-um), or greater multiangular.

The palm of the hand is made up of the five metacarpal bones. These are small, long bones, each with a base, shaft and a head. They radiate out from the wrist bones like the spokes of a wheel rather than being parallel. They each articulate with a proximal phalanx (FAY-langks) of a finger. Each finger, except the thumb, has three phalanges (fah-LAN-jeez): a proximal, a middle and a terminal, or distal, phalanx. The thumb has only a proximal and distal phalanx. The bones of the lower extremities include the pelvic girdle, which supports the trunk and provides attachment for the legs. |

Other bones of the lower extremity include the thigh, the kneecap, the shin, the calf, the ankle bones, the foot and the toes.The pelvic girdle is actually made up of two hip or coxal bones that articulate with one another anteriorly at the pubic symphysis. Posteriorly, they articulate with the sacrum. This ring of bone is known as the pelvis.It consists of the paired hip bones or coxal bones. Each hipbone consists of three fused parts: 1. the ilium (ILL-ee-um), 2. the ischium (ISS-kee-um) 3. and the pubis (PYOO-bis).The ilium is the uppermost and largest portion of the hipbone. It forms the expanded prominence of the upper hip or iliac crest. It is wider and broader in females and smaller and narrower in males. Its crest is projected into the anterior superior iliac spine and the anterior inferior iliac spine.The ischium is the strongest portion of a hipbone and is directed slightly posteriorly. Its curved edge is viewed from the front as the lowermost margin of the pelvis. It has the rounded and thick ischial tuberosity, which you sit on, and thus bears the weight of the body in the sitting position.The pubis is superior and slightly anterior to the ischium. Between the pubis and the ischium is the large obturator (OB-tuh-ray-tohr) foramen. This is the largest foramen in the body and allows for the passage of nerves, blood vessels and tendons.On the lateral side of the hip just above the obturator foramen is the deep socket called the acetabulum (ass-eh-TAB-you-lum). All three parts of the pelvic bone meet and unite in this socket. It also receives the head of the femur to help form the hip joint.The femur (FEE-mehr), or thigh, is the largest and heaviest bone of the body. This single large bone of the upper leg is not in a vertical line with the axis of the erect body. Rather it has a unique engineering design that allows it to bear and distribute the weight of the body. It is positioned at an angle, slanting downward and inward so that the two femurs appear as a large letter V. Its upper extremity bears a large head that fits into the acetabulum of the pelvic bone, with an anatomic neck. Its lower portion is widened into a large lateral condyle and an even larger medial condyle. It articulates distally with the tibia.
The patella (pah-TELL-ah), or kneecap, is the largest of the sesamoid bones. It is somewhat flat and triangular, lying right in front of the knee joint, and is enveloped within the tendon of the quadriceps femoris muscle. Its only articulation is with the femur. It is a movable bone, and it increases the leverage of the muscles that straighten out the knee.The tibia (TIB-ee-ah) is the larger of the two bones forming the lower leg. It is also known as the shin. The rounded condyles of the femur rest on the flat condyle at the proximal end of the tibia.The fibula (FIB-you-lah) is also known as the calf. In proportion to its length, it is the most slender bone of the body. It lies parallel with and on the lateral side of the tibia. It does not articulate with the femur but attaches to the proximal end of the tibia via its head.The bones of the ankle are known as the tarsal bones. The seven short tarsal bones resemble the carpal bones of the wrist but are larger. They are arranged in the hindfoot and forefoot. The tarsal bones of the hindfoot are the calcaneus calcaneus (kal-KAY-nee-us), sometimes called the calcaneum, which is the largest of the tarsal bones and forms the heel; the talus or ankle bone, the navicular (nah-VIK-you-lar) and the cuboid (KYOO-boyd). Because the calcaneus or heel bone receives the weight of the body when walking, it has developed as the largest of the tarsal bones. The tarsal bones of the forefoot are the medial (I), intermediate (II) and lateral (III) cuneiforms (kyoo-NEE-ih-formz).The rest of the forefoot bones are the metatarsals and phalanges. There are five metatarsal bones in the forefoot. Each is classified as a long bone based on shape and each has a base, shaft and a head. The heads formed at the distal ends of the metatarsals form what we call the ball of the foot. The bases of the first, second and third metatarsals articulate with the three cuneiforms; the fourth and fifth metatarsals articulate with the cuboid. The intrinsic muscles of the toes are attached to the shafts of the metatarsals. The first metatarsal is the largest due to its weight-bearing function during walking.

The phalanges of the toes are classified as long bones despite their short length because again they have a base, shaft and head. They have the same arrangement as the phalanges of the fingers. There are two phalanges in the great toe, proximal and distal. The proximal one is large due to its weight-bearing function when walking. The other four toes have three each, proximal, middle and distal phalanges.The bones of the foot are arranged in a series of arches that enable the foot to bear weight while standing and to provide leverage while walking. There are two longitudinal arches and one transverse arch. The medial longitudinal arch is formed by the calcaneus, talus, navicular, the three cuneiforms and the three medial metatarsals. This is the highest arch of the foot and can easily be noted. The lateral longitudinal arch is much lower and is formed by the calcaneus, the cuboid and the two lateral metatarsals. The transverse arch is perpendicular to the longitudinal arches and is most pronounced at the base of the metatarsals.The term pes planus, or flatfoot, indicates a decreased height of the longitudinal arches. It rarely causes any pain and can be inherited or result from muscle weakness in the foot.Phalanges are the bones of the fingers and toes.The iliac crest is the expanded prominence of the upper hip boneThe largest of the sesamoid bones is the kneecap, known as the: patellaThe strongest portion of the pelvis, the bone that bears the weight of the body in the sitting position, is known as the: ischiumThe largest and longest bone of the upper arm is the: humerusThe highest arch of the foot, formed by the calcaneus, talus, navicular, cuneiforms, and the medial metatarsal bones, is called the: medial longitudinal archCHAPTER 8An articulation is a place of union or junction between two or more bones, regardless of the degree of movement allowed by this union. The sutures between various bones of the skull are considered as much a part of the articular system as the knee or elbow joint. When we think of a joint, we tend to think of the freely moving joints such as the shoulder or hip joint, but other types of joints have limited or no movement at all occurring at their site.Joints are classified into three major groups according to the degree of movement they allow (function) and the type of material that holds the bones of the joint together (structure).Synarthroses (sin-ahr-THRO-seez) are joints or unions between bones that do not allow movement. Syn as a prefix means joined together. There are three examples of synarthroses or immovable joints: 1. Suture 2. Syndesmosis 3. Gomphosis

The first type is a suture (SOO-chur). A suture is an articulation in which the bones are united by a thin layer of fibrous tissue. The suture joints of the skull are examples. Recall from Chapter 7 that the bones of the skull are formed by intramembranous ossification. The fibrous tissue in the suture is the remnant of that process and helps form the suture.

The second example is a syndesmosis (sin-dez-MOH-sis). Syndesmoses (plural) are joints in which the bones are connected by ligaments between the bones. Examples are where the radius articulates with the ulna and where the fibula articulates with the tibia. These bones move as one when we pronate and supinate the forearm or rotate the lower leg. Some authors consider syndesmosis as an example of an amphiarthrosis (little movement).The third example is a gomphosis (gohm-FOH-sis). Gomphoses (plural) are joints in which a conical process fits into a socket and is held in place by ligaments. An example is a tooth in its alveolus (socket), held in place by the periodontal ligament.Amphiarthroses (am-fee-ahr-THRO-seez) are joints that allow only slight movement. There are two examples of amphiarthroses: 1. symphysis 2. synchondrosisThe first example of an amphiarthrosis is a symphysis (SIM-fah-sis). Symphyses (plural) are joints in which the bones are connected by a disk of fibrocartilage. An example of a symphysis is the pubic symphysis where the two pelvic bones at the pubis are joined. During delivery this joint allows the pelvic bone slight movement to increase the size of the birth canal.The second example of an amphiarthrosis is a synchondrosis (sin-kon-DRO-sis). Synchondroses (plural) are joints in which two bony surfaces are connected by hyaline cartilage. The cartilage is replaced by permanent bone later in life. An example of a synchondrosis is the joint between the epiphyses (flared portions) and the diaphysis (shaft) of a long bone. Remember from Chapter 7 that this is the location of the growth plate and where long bones develop longitudinally by endochondral ossification. Some authors consider a synchondrosis as an example of a synarthrosis (no movement).Diarthroses (dye-ahr-THRO-seez) or synovial joints are freely moving joints or articulations. They are always characterizied by the presence of a cavity enclosed by a capsule. This cavity may contain various amounts and concentrations of a number of tissues. The cavity may be enclosed by a capsule of fibrous articular cartilage. Ligaments can reinforce the capsule, and cartilage will cover the ends of the opposing bones. This capsule will be lined on the inside with synovial membrane, which produces synovial fluid. Most joints of the upper and lower limbs are diarthroses.The articular cartilage in the joint provides a smooth, gliding surface for opposing bone. This is made possible because of the lubrication caused by the synovial fluid. The opposing bones do not wear or erode over time due to the constant friction caused by movement at the joint. Articular cartilage has a limited blood supply. It receives its nourishment from the synovial fluid and from a small number of subsynovial blood vessels at the junction of the cartilage and the joint capsule. Synovial fluid has two functions: creating a smooth gliding surface for opposing bones and nourishing the articular cartilage. Cartilage also functions as a buffer between the vertebrae in the spinal column to minimize the forces of weight and shock from running, walking or jumping.Collagenous fibers connecting one bone to another in the synovial joint form the capsule enclosing the joint. The range of motion of the joint is related to the laxity or looseness of the joint. This is directly related to the structure of the capsule and how it is formed over the opposing bones. In the shoulder joint, which has the greatest range of movement, the capsule is loose enough to permit the head of the humerus to be drawn away from the glenoid fossa of the scapula. However, in the hip joint the range of motion is much more restricted, because the capsule is thicker and shorter and the head of the femur sits deeply in the acetabulum of the pelvic bone. The femur is also connected to the acetabulum by a series of strong ligaments. This structure is necessary because of the need for greater strength in this joint.In addition to the above tissues that make up the capsule, muscles and their tendons can also be found as the outermost layer of the capsule. They provide an important mechanism for maintaining the stability of a diarthrosis or synovial joint. They have advantages over ligaments because during both relaxation and contraction they maintain the joint surfaces in firm contact at every position of the joint.In summary, synovial joints have a number of functions. First, they bear weight and allow movement; second, their construction in the form of a capsule made of ligaments, tendons, muscles and articular cartilage provide stability; and third, synovial fluid lubricates the joint and nourishes the cartilage.Synovial joints are characterized by the presence of a(n) cavity enclosed by a(n) capsule.A diarthrosis joint provides a smooth gliding surface because of lubrication.A buffer between two weight-bearing bones is provided by cartilage.The joint providing the greatest range of motion in the body is found in the shoulder.Functions of the synovial joints include bearing weight, stability and lubrication.Joints are classified by structure, type of material holding the joint together, and function, degree of movement they allow.Skull joints are called sutures.Those joints allowing only slight movement are amphiarthrosis.A joint in which two bony surfaces are connected by hyaline cartilage is a(n) synchondrosis.Synovial joints are also called diarthrosis.Inflammation of the synovial bursa, which can be caused by excessive stress or tension placed on the bursa, is known as: bursitisAn accumulation of uric acid crystals in the joint at the base of the large toe and other joints of the feet and legs causes a condition known as: goutDegenerative joint disease, a condition affecting the weight-bearing joints, is also known as: osteoarthritisA joint in which a conical process fits into a socket and is held in place by ligaments is known as a(n): gomphosisA place of union or junction between two or more bones, regardless of the degree of movement allowed by this union, is known as a(n): articulationCreating a smooth gliding surface for opposing bones and nourishing the articular cartilage are the two functions of: synovial fluidInflammation of a joint is called arthritis.Cassandra is in the middle of giving birth to her first child. Her partner is amazed at the ability of the human body to stretch and allow an 8-pound infant through the birth canal. Along with the stretching of soft tissue, what joint also allows the pelvic bones to move and increase the birth canal opening? How would you classify this joint? Pubic symphysis; amphiarthrosis

Flexion (FLEK-shun) is the act of bending or decreasing the angle between bones.Extension (eks-TEN-shun) is the act of increasing the angle between bones and is the opposite of flexion. Refer to the figure on the right for flexion/extension and hyperextension.Hyperextension increases the joint angle beyond the anatomic position.Abduction(ab-DUCK-shun) is moving the bones or limb away from the midline of the body while the opposite is adduction (add-DUCK-shun), which is moving the bone or limb toward the midline of the body.Rotation (row-TAY-shun) is the act of moving the bone around a central axis; the plane of rotational motion is perpendicular to the axis, as when rotating our head.Circumduction (sir-kum-DUCK-shun) is moving the bone in such a way that the end of the bone or limb describes a circle in the air and the sides of the bone describe a cone in the air.

Supination (soo-pin-NAY-shun) and pronation (proh-NAY-shun) refer to the movement of the forearm and hand. Supination is moving the bones of the forearm so that the radius and ulna are parallel. If the arm is at the side of the body, the palm is moved from a posterior to an anterior position; if the arm is extended, the palm faces up as in carrying a bowl of soup. Pronation is moving the bones of the forearm so that the radius and ulna are not parallel. If the arm is at the side of the body, the palm is moved from an anterior to a posterior position; if the arm is extended, the palm faces down.Eversion (ee-VER-zhun) and inversion (in-VER-zhun) refer to movements of the foot. Eversion is moving the sole of the foot outward at the ankle while inversion is moving the sole of the foot inward at the ankle.Retraction (rih-TRACK-shun) is moving a part of the body backward on a plane parallel to the ground. Refer to the figure on the right for protraction and retraction of the lower jaw.Elevation is raising a part of the body; depression is lowering a part of the body. Refer to the figure on the right for elevation and depression of the shoulder.Opposition is movement that occurs only with the thumb and is unique to primates. It occurs when the tip of the thumb and the fingers are brought together. The action allows us to use tools as when writing with a pen. Reposition occurs when the digits return to their normal positions.Dorsiflexion is raising the foot up at the ankle joint and plantar flexion is pushing the foot down at the ankle joint, actions we do when walking.If a joint is forced beyond its normal range of extension, it is hyperextended.Supination is a movement placing the palm in an anterior position.Moving the palm of the hand so that it faces down is called pronation.Move the body forward for protraction and backward for retraction.Only primates can perform the movement called opposition.Hyperextension is the act of increasing the joint angle beyond the anatomical position.Dorsiflexion is the act of raising the foot up at the ankle joint.Abduction is the act of moving the bones or limb away from the midline of the body.Moving the bone in such a way that the end of the bone or limb describes a circle in the air is called circumduction.The act of moving the bone around a central axis, with the plane of rotational motion perpendicular to the axis, is known as: rotationMovement of a bone or limb toward the midline of the body is known as: adductionMovement of the sole of the foot outward at the ankle is known as: eversionThe movement of raising a part of the body is known as: elevationThe act of bending or decreasing the angle between bones is known as: flexionThe act of increasing the angle between bones is: extensionMoving the foot down at the ankle joint is known as: plantar flexionThe movement that occurs only with the thumb and allows performance tasks such as writing with a pen is known as: oppositionWhile working out at the gym, Tameka overheard one of the trainers say, “Come on, flex those triceps!” If you contract your triceps brachii, what movement results? Extension of forearmThere are six types of freely moving or synovial joints. Refer to the figure for the geometric structure and examples of these joints that permit certain types of movements: 1. ball-and-socket joint 2. hinge joint 3. pivot joint 4. condyloid joint 5. saddle joint 6. gliding jointA ball-and-socket joint is an example of a multiaxial joint. In this type of joint, a ball-shaped head fits into a concave socket. Two examples are the ball-shaped head of the femur fitting into the concave socket of the acetabulum of the pelvic bone and the head of the humerus fitting into the glenoid fossa of the scapula. This type of joint provides the widest range of motion. Movement can occur in all planes and directions. Of the two ball-and-socket joints, the hip and the shoulder, the shoulder has the widest range of movement.Hinge Joint | The hinge joint is structured in such a way that a convex surface fits into a concave surface. In this type of a joint, motion is limited to flexion and extension in a single plane. Two examples are the elbow and knee joint. Because motion is restricted to one plane these joints are also called uniaxial hinge joints. Refer to the figure on the right to see the structure of the uniaxial knee joint. Other uniaxial hinge joints are the middle and distal phalanges of the fingers and toes. |

The pivot joint is another uniaxial joint because motion is limited to rotation in a single plane. The joint is constructed in such a way that a pivot-like process rotates within a bony fossa around a longitudinal axis. One example is the joint between the atlas vertebra (the pivot process) that rotates within the bony fossa of the axis vertebra.

The condyloid (KON-dih-loyd) joint, sometimes called an ellipsoidal joint, is a biaxial joint that consists of an oval-shaped condyle that fits into an elliptical cavity. Motion is possible in two planes at right angles to each other. The wrist joint between the radius of the forearm and some of the carpal bones of the wrist is a condyloid joint. The hand can be flexed and extended in one plane like raising your hand in a sign to stop and returning it to a downward position. It can also be abducted and adducted like waving good-bye when moving the hand from side to side.Saddle Joint | The saddle joint, another biaxial joint, is a bit more complex in its structure. In this type of a joint, one articular surface is concave in one direction and convex in the other (the trapezium, a carpal bone of the wrist), while the other articular surface is reciprocally convex and concave (the metacarpal bone in the thumb). Thus, the two bones fit together. Refer to the figure on the right to study its construction. Movement is possible in two planes at right angles to each other: flexion and extension plus abduction and adduction. This construction also permits opposition of the thumb, an evolutionary advancement allowing phenomenal dexterity of the hand to grasp and use tools. |
The gliding joint is the last type of synovial joint and is a multiaxial joint. This type of joint is formed by either opposing plane surfaces or slightly convex and concave surfaces. This type of joint only allows gliding movement. Examples of gliding joints are those between the superior and inferior articular processes of the vertebrae in the spine.A ball-and-socket joint will have a ball-shaped head fitting into a(n) concave socket.An example of a hinge joint is the elbowA condyloid joint is also known as a(n) ellipsoidal joint.The thumb is an example of a(n) saddle joint.Gliding joints are found in the vertebrae.A(n) hinge joint is a type of joint in which the movement is limited to flexion and extension in a single plane.

Bursae (burr-SEE) are closed sacs with a synovial membrane lining. Bursae can be found in the spaces of connective tissue between tendons, ligaments and bones. Bursae are found wherever friction could develop during movement. They facilitate the gliding of either muscle over muscle or tendons over bony ligamentous surfaces. Bursae are classified into three types based on where they are found: 1. subcutaneous bursae 2. subfascial bursae 3. subtendinous bursae

Subcutaneous bursae are found under (sub) the skin (cutaneous) wherever the skin is on top of an underlying bony process (e.g., the knee joint). Between the patella or kneecap and its overlying skin is a subcutaneous bursa preventing friction between bone and skin.Subfascial (sub-FASH-ee-al) bursae are located between muscles. They are found above the fascia (FASH-ee-ah) of one muscle and below the fascia of another. The fascia is the fibrous connective tissue that covers the epimysium of a muscle bundle. We will discuss fascia in Chapter 9.Subtendinous bursae are found where one tendon overlies another tendon or where one tendon overlies some bony projection, as in the shoulder.Closed sacs with a synovial membrane lining that can be found in the spaces of connective tissue between tendons, ligaments, and bones are known as: bursae |
CHAPTER 9
As you read this introduction, skeletal muscles are moving your eyes to read the words. Muscles allowed you to first pick up this book and open it to the correct page. You walked to your desk, and you took this book off a shelf. All of these actions allowed you to function in your environment. In addition, smooth muscle is containing the blood in your arteries and veins, food is being pushed through your digestive tract and urine is being transported from your kidneys via the ureters to your bladder. Meanwhile, cardiac muscle is pumping the blood, carrying oxygen and nutrients to your body cells and carrying away waste.
Muscles make up about 40% to 50% of the body’s weight. They allow us to perform extraordinary physical feats of endurance (running, playing sports) and grace (ballet, figure skating). When they contract, they bring about movement of the body as a whole and cause our internal organs to function properly. Muscles of the diaphragm, chest and abdomen allow us to breathe.
From the discussion of tissues in Chapter 5, you recall that there are three types of muscle tissue: skeletal or striated, smooth or visceral and cardiac. Recall that skeletal muscle is voluntary, that is, we can control its contraction. Under the microscope, skeletal muscle cells are multinucleated and striated; we can see alternating dark and light bands. Smooth muscle, on the other hand, is involuntary, uninucleated and nonstriated. It is found in places like the digestive tract. Cardiac muscle is involuntary, striated and uninucleated and is found only in the heart.
Skeletal muscle is striated and Multinucleated
Myalgia is muscle pain.
An increase in the size of a muscle caused by an increase in the bulk of muscle cells through exercise is known as hypertrophy.
Spastic and painful contractions of muscles that occur because of an irritation within the muscle are known as cramps
A decrease in muscle bulk due to a lack of exercise, as when a limb is in a cast for a prolonged period, is known as atrophy
An inherited muscular disorder, occurring most often in males, in which the muscle tissue degenerates over time, resulting in complete helplessness is known as muscular dystrophy.
A condition, commonly occurring in individuals who are bedridden, in which a muscle shortens its length in the resting state is known as contracture.

Mature skeletal or striated muscle cells are the longest and most slender muscle fibers, ranging in size from 1 to 50 mm in length and 40 to 50 micrometers in diameter. Because of this unique structure of the cell, that is, their length being much greater than their width, skeletal muscle cells are often referred to as skeletal muscle fibers.
In addition, each muscle cell or fiber is multinucleated and is surrounded by a special cell membrane. This cell membrane is electrically polarized and is called a sarcolemma (sahr-koh-LEM-ah). The sarcolemma is surrounded by the first of three types of connective tissue found in a muscle the endomysium (in-do-MISS-ee-um), which is delicate connective tissue.
As we study the figure, we see that the entire muscle consists of a number of skeletal muscle bundles called fasciculi (fah-SICK-you-lye). Each individual bundle of muscle cells, or fascicle (FASS-ih-kl), is surrounded by another layer of connective tissue called the perimysium (pair-ih-MISS-ee-um). This is visible to the naked eye. This perimysium connects with the coarse irregular connective tissue that surrounds the whole muscle called the epimysium (ehp-ih-MISS-ee-um). These three layers of connective tissue act like cement holding all of the muscle cells and their bundles together. In addition, a layer of areolar tissue covers the whole muscle trunk on top of the epimysium and is called the fascia (FASH-ee-ah).
When skeletal muscle is viewed under a microscope, the cells appear to have alternating dark and light bands referred to as cross-striations. The striations are due to an overlapping of the dark and light bands of protein on the myofibrils. The dark bands are made of the thick filaments of the protein myosin. Being thick, they therefore appear dark and are called the A bands (hint to remember: the second letter in the word dark is A). The light bands are made of the thin filaments of the protein actin; being thin, they appear light and are called the I bands (hint to remember: the second letter in the word light is I).
A number of other markings are important to note. A narrow, dark staining band found in the central region of the I band that looks like a series of the letters Z one on top of another is called the Z line. A slightly darker section in the middle of the dark A band is called the H band or H zone. This is where the myosin filaments are thickest and where there are no cross-bridges on the myosin filaments. The area between two adjacent Z lines is called a sarcomere (SAHR-koh-meer). It is here at the molecular level that the actual process of contraction occurs via chemical interactions, which is discussed later.
Electron microscopy has also revealed the fact that muscle fibrils (thousands of tiny units that make up a muscle cell) are surrounded by structures made up of membranes in the form of vesicles and tubules. These structures constitute what is referred to as the sarcotubular (sahr-koh-TYOO-byoo-lar) system. The sarcotubular system is made up of two components: 1. the T system or tubules 2. the sarcoplasmic reticulum (reh-TIK-you-lum).
The tubules of the T system are continuous with the cell membrane or sarcolemma of the muscle fiber and form a grid perforated by individual muscle fibrils. The sarcoplasmic reticulum forms an irregular curtain around each of the fibrils. Again refer to the figure on the right for these complex structures. This T system functions in the rapid transmission of a nerve impulse at the cell membrane to all the thousands of fibrils that make up the muscle cell. A muscle cell could be thought of as a single thread of cloth.
If you put a single thread under a microscope, you would see that it was made up of hundreds of smaller units of fiber. Hence, just like the thread, the muscle cell or fiber is made up of thousands of smaller units called myofibrils. At the molecular level, each myofibril is made up of microscopic filaments of the proteins myosin (which is thick and looks dark under the microscope) and actin (which is thin and looks light under the microscope).
Because their length is greater than their width, skeletal muscle cells are referred to as muscle Fibers.
A bands are the dark bands and I bands are the light bands.
There are no cross-bridges in the H zone.
The actual process of contraction occurs in the area called the sarcomere.
Muscle fibrils are surrounded by membranes in the form of vesicles and tubules.
An irregular curtain around each of the fibrils is the sarcoplasmic reticulum.
Myofibrils have dark bands, known as A bands, composed of the protein myosin.
All of the muscle cells or fibers innervated by one motor neuron is called a motor unit because they (the muscle cells) are always excited simultaneously and therefore contract together. It is important to remember that the terminal divisions or axon endings of a motor neuron are distributed throughout the belly of the whole muscle. Stimulation of a single motor unit causes weak but steady contractions in a broad area of the muscle rather than a strong contraction at one tiny specific point.
Muscles controlling very fine movements (like muscles that move the eye) are characterized by the presence of only a few muscle fibers in each motor unit. Another way to state this would be the ratio of nerve fibers to muscle cells is high. For example, each motor unit present in the ocular muscle contains about 10 muscle cells. However, gross movements (like lifting an object with your hand) will contain a motor unit with 200 or more muscle cells. On the average, a single motor nerve fiber innervates about 150 muscle cells.
Muscle cells possess four properties: excitability, conductivity, contractility and elasticity. Muscle fibers can be excited by a stimulus. In our bodies this stimulus is a nerve cell. In the laboratory, we can stimulate and excite a muscle with an electrical charge. Besides the property of excitability, all protoplasm in the cell possesses the property of conductivity, which allows a response to travel throughout the cell. The type of response will depend on the type of tissue that is excited. In muscle cells, the response is a contraction. Elasticity then allows the muscle cell to return to its original shape after contraction. Muscle contraction is caused by the interactions of three factors: neuroelectrical factors, chemical interactions and energy sources. Surrounding the muscle fiber’s membrane or sarcolemma are ions. The ionic distribution is such that there is a greater concentration of potassium ions (K1) inside the cell than outside the cell, whereas there is a greater concentration of sodium ions (Na1) outside the cell membrane than inside the cell. |

These ions are all positively charged. Because of an uneven distribution of these ions, there is an electrical distribution around the muscle cell. The inside of the cell is negatively charged and the outside of the cell is positively charged. This situation is known as the muscle cell’s resting potential.As the nerve impulse reaches the neuromuscular junction where the axon terminals of the nerve cell are in close proximity to the muscle and its numerous cells, it triggers the axon terminals to release a neurotransmitter substance called acetylcholine (ah-seh-till-KOH-leen). This chemical substance affects the muscle cell membrane. It causes the sodium ions (which were kept outside during the resting potential) to rush inside the muscle cell.This rapid influx of sodium ions creates an electrical potential that travels in both directions along the muscle cell at a rate of 5 meters per second. This influx of Na1 causes the inside of the cell to go from being electrically negative to being positive. This is a signal to the muscle cell to generate its own impulse called the action potential. This is the signal to contract. Meanwhile the potassium ions that were kept inside begin to move to the outside to restore the resting potential, but they cannot change back to the resting potential situation because so many sodium ions are rushing in.

This action potential not only travels over the surface of the muscle cell membrane but passes down into the cell by way of the T tubules and also deep into all the cells that make up the muscle. This action potential causes the sarcoplasmic reticulum to release stored calcium ions into the fluids surrounding the myofibrils of the muscle cell. Surrounding the actin myofilaments are two inhibitor substances: troponin (TRO-poh-nin) and tropomyosin (troh-poh-MY-oh-sin).These substances keep the actin and myosin protein filaments from interacting. However, when calcium ions are released by the sarcoplasmic reticulum, the action of these inhibitor substances is negated. It is the release of the calcium ions that brings about the contractile process at the molecular level in the myofilaments. When the action potential ceases to stimulate the release of the calcium ions from the reticulum, these ions begin to return and recombine with the sarcoplasmic reticulum.What causes this to happen is the sodium-potassium pump of the muscle cell membrane. As the sodium ions rushed into the cell and potassium rushed out to try to restore the original resting potential but could not do so, the sodium-potassium pump began operating to restore the ionic distribution to its normal resting potential. Contraction occurs in a few thousandths of a second and once the sodium-potassium pump restores ionic distribution, contraction ceases because the action potential is now stopped and all the calcium ions are once again bound to the reticulum. A continued series of action potentials is necessary to provide enough calcium ions to maintain a continued contraction. Now let’s discuss the chemical interactions and those calcium ions.In 1868 a German scientist named Kuhne extracted a protein, which he called myosin, from muscle using a strong salt solution. In 1934, myosin was shown to gel in the form of threads. Shortly thereafter, it was discovered that the threads of myosin became extensible when placed near adenosine triphosphate (ATP). It was not until 1942 that scientists discovered that this myosin was not homogeneous, and that in fact there was another protein in the muscle distinct from myosin and it was called actin. In actuality, the actin unites with the myosin to form actomyosin during the contraction process.The release of the calcium ions from the sarcoplasmic reticulum inhibits the activity of the troponin and the tropomyosin, which have kept the actin and myosin myofilaments apart. The calcium ions attach to the troponin and now cause the myosin to become activated myosin. The myosin filaments have large heads that contain ATP molecules. The activated myosin releases the energy from the ATP at the actin active site when the myosin links up and forms actomyosin. The head linkage makes a cross-bridge that pulls the actin filaments inward among the myosin filaments and breaks down the ATP into adenosine diphosphate (ADP) and PO4 and the release of energy, which causes contraction.The shortening of the contractile elements in the muscle is brought about by the pulling of the actin filaments over the myosin filaments. The width of the A bands remains constant while the Z lines move closer together during contraction.When the sodium-potassium pump has restored the resting potential of the cell and sodium ions are back outside and potassium ions are back inside the cell, the action potential ceases and calcium ions get reabsorbed by the sarcoplasmic reticulum. Now contraction ceases and the actin filaments get released from the myosin and the Z lines move further apart. This whole complex process occurs in 1/40 of a second.Keep in mind that we discussed only one small part of a muscle cell’s filaments. There are thousands of myofilaments in a single muscle cell, and a muscle like your biceps contains hundreds of thousands of muscle cells, all interacting and coordinating together at the molecular level to bring about contraction.Muscle cells convert chemical energy (ATP) into mechanical energy (contraction). This source of energy is ATP molecules (review Chapter 4). Actin + myosin + ATP-›actomyosin + ADP + PO4 + energy (causing contraction). The energy given off by the breakdown of ATP is used when the actin and myosin filaments intermesh. ATP is synthesized by glycolysis, the Krebs citric acid cycle, electron transport and, in muscle cells, by the breakdown of phosphocreatine. |

In glycolysis, you will recall from Chapter 4, glucose present in the blood enters cells where it is broken down through a series of chemical reactions to pyruvic acid. A small amount of energy is released from the glucose molecule with a net gain of two molecules of ATP.

In the Krebs citric acid cycle and electron transport, if oxygen is present, the pyruvic acid is further broken down into CO2 and H2O and 36 more ATP molecules. If oxygen is not available to the muscle cell, the pyruvic acid changes to lactic acid and builds up in the muscle cell with only two ATP produced until oxygen again becomes available.

Muscle cells have two additional sources of ATP. Phosphocreatine (fos-foh-KREE-ah-tin) is found only in muscle tissue and provides a rapid source of high-energy ATP for muscle contraction. When muscles are at rest, excess ATP is not needed for contraction so phosphate is transferred to creatine to build up a reserve of phosphocreatine. During strenuous exercise, the phosphocreatine takes up ADP to release ATP and creatine, thus supplying the muscle with an additional supply of ATP. The overall reaction, which goes in both directions is phosphocreatine + ADP ‹-›creatine + ATP.In addition, skeletal muscle cells can take up free fatty acids from the blood and break them down as another source of energy into CO2, H2O and ATP. Of course, during any contraction, heat is produced as a waste product.In summary, muscle cells have four sources of ATP for the energy of contraction: 1. Glucose + 2 ATP--> CO2 + H2O + 38 ATP (aerobic) 2. Glucose + 2 ATP --> 2 lactic acid + 2 ATP (anaerobic) 3. Phosphocreatine + ADP--> creatine + ATP 4. Free fatty acids--> CO2 + H2O + ATP

When the contraction of a skeletal muscle is studied in the laboratory by applying an electrical charge to the muscle, the analysis of the contraction is called a muscle twitch.

This reveals a brief latent period directly following stimulation just before contraction begins. This latent period is followed by a period of contraction followed by a period of relaxation. This latent period occurs because the resting potential of the muscle cells must change into the electrical potential as sodium ions rush in. This is caused by the acetylcholine released by the nerve cell’s axon terminals into the neuromuscular junction. The electrical potential then becomes the action potential as the signal travels down the T tubules to the sarcoplasmic reticulum. Then calcium ions get released into the fluids around the myofibrils of actin and myosin and contraction occurs. Once the sodium-potassium pump operates, calcium gets reabsorbed and relaxation occurs.The strength of the contraction depends on a number of factors: the strength of the stimulus (a weak stimulus will not bring about contraction); the duration of the stimulus (even if the stimulus is quite strong, if it is applied for a millisecond it may not be applied long enough for it to be effective); the speed of application (a strong stimulus applied quickly and quickly pulled away may not have time enough to take effect even though it is quite strong); the weight of the load (one can pick up a waste basket with one hand but not a dining room table); and, finally, the temperature (muscles operate best at normal body temperature 37°C or 98.6°F in humans).A stimulus strong enough to elicit a response in an individual muscle cell will produce maximal contraction. The contraction either occurs or it does not. This is known as the all-or-none law.Tone is defined as a property of muscle in which a steady or constant state of partial contraction is maintained in a muscle. Some muscle cells in a muscle will always be contracting while other muscle cells are at rest. Then those at rest will contract, while those that were contracting will go into relaxation.

This allows us, for example, to maintain body posture for long periods of time without showing any evidence of tiring. This is accomplished because nerve stimuli alternate between various groups of muscle cells, thus allowing all to have periods of rest. Tone results in skeletal muscles exhibiting a certain degree of firmness as they maintain a slight and steady pull on attached bones. Tone maintains pressure on abdominal contents, maintains blood pressure in arteries and veins and assists in digestion in the stomach and intestines.

There are two types of contraction. When lifting a weight, muscles become shorter and thicker. In this type of contraction, tone or tension remains the same and is referred to as isotonic contraction. When we push against a wall or attempt to lift a huge boulder, the muscles involved remain at a constant length while the tension against the muscle increases, and this is known as isometric activity. From this fact, a whole series of exercises have been developed called isometric exercises (like locking fingers of opposite hands and pulling to develop the biceps). These exercises help develop tone or firmness in muscles.The all-or-none law states that a muscle contraction either occurs or it doesn’t.A property of muscle whereby a steady or constant state of partial contraction is maintained is known as tone.The concept of a stimulus being strong enough to elicit a maximal contraction of an individual muscle cell, or no contraction at all, is known as (the) all-or-none law.When the contraction of a skeletal muscle is studied in the laboratory by applying an electrical charge to the muscle, the analysis of the contraction is called a muscle twitch.Smooth muscle is found in hollow structures of the body like the intestines, blood vessels and urinary bladder. It cannot be controlled at will because it is under the control of the autonomic nervous system and also may be hormonally stimulated. |
Each smooth muscle cell contains a single large nucleus and because its fiber is more delicate than skeletal muscle, cross-striation of the myosin and actin arrangements is not visible. The cells connect by fibrils extending from one cell to another closely adjoining cell.

In hollow structures like the small intestine, the smooth muscle is arranged in two layers, an outer longitudinal layer and an inner circular layer. Contraction of these two layers, with the circular layer contracting first, results in reducing both the length of the tube and the circumference of the tube. This contraction pushes whatever is in the tube in a forward direction, for example, digested food or chyme in the intestine or blood in the arteries and veins. Smooth muscle cells produce a slower contraction than skeletal muscle, but smooth muscle contraction allows greater extensibility of the muscle

The actin and myosin fibers are not so regularly arranged in smooth muscle as in striated muscle. Therefore, contraction occurs in a similar way but without the regular rearrangement of the fibrils. The fibrils do slide together and rhythmically shorten the cell, but a slow wave of contraction passes over the entire muscle mass as the nerve impulse reaches a cell and gets transmitted to the remainder of the cells or fibers.

Cardiac muscle cannot be influenced at will because it, like smooth muscle, is under the control of the autonomic nervous system. It is uninucleated, similar to smooth muscle; however, it is striated like skeletal muscle. Cardiac muscle also has another unique quality. If one muscle cell is stimulated, all the muscle cells or fibers are stimulated so all the muscle cells contract together. Also, the muscle cell that contracts the fastest will control the speed of other muscle cells, causing them all to contract at the faster rate. The rapid rhythm of cardiac muscle is the result of a special property of this type of cell to receive an impulse, contract, immediately relax and then receive another impulse. These events all occur about 75 times a minute. However, the period of an individual contraction is slower in cardiac (about 0.8 second) as opposed to skeletal muscle, which is much faster (about 0.09 second). | |

If rapid, uncontrolled contraction of individual cells in the heart occurs, this is called fibrillation. This results in the heart’s inability to pump the blood properly and can result in death. |
The muscle that is nonstriated and found in hollow structures is smooth.
Smooth muscle contraction occurs without the regular rearrangement of fibrils.
Cardiac and smooth muscle is under the control of the autonomic nervous system.
The rapid, uncontrolled contraction of individual cells in the heart, resulting in the heart's inability to pump blood properly is known as fibrillation
Fibrillation of cardiac muscle can result in death

Muscles can be named according to their action (adductor, flexor, extensor); according to shape (quadratus, trapezius); according to origin and insertion (sternocleidomastoid); according to location (e.g., frontalis, tibialis, radialis); according to their number of divisions (e.g. biceps, triceps, quadriceps); and, finally, according to the direction their fibers run (transverse, oblique).

The more fixed attachment of a muscle that serves as a basis for the action is the origin. The movable attachment, where the effects of contraction are seen, is called the insertion. The origin is the proximal (closer to the axial skeleton) attachment of the muscle to a bone; the insertion is the distal (farthest away from the axial skeleton) attachment to the other bone. Most voluntary or skeletal muscles do not insert directly to a bone, but rather they insert through a strong, tough, nonelastic, white collagenous fibrous cord known as a tendon. Tendons vary in their lengths from a fraction of an inch to those more than a foot in length, like the Achilles tendon in the lower leg, which inserts on the heel bone. If a tendon is wide and flat, it is called an aponeurosis (ap-oh-noo-ROH-sis).

Muscles are found in many shapes and sizes. Muscles that bend a limb at a joint are called flexors. Muscles that straighten a limb at a joint are called extensors. If a limb is moved away from the midline, an abductor is functioning; however, if the limb is brought in toward the midline, an adductor is functioning. The muscles rotating an involved limb are rotators. In movements of the ankle, muscles of dorsiflexion turn the foot upward, and muscles of plantar flexion bring the foot toward the ground. In movements of the hand, turning the forearm when it is extended out so that the palm of the hand faces the ground is pronation, whereas turning the forearm so that the palm faces upward is supination. Levators raise a part of the body, and depressors lower a part of the body. See Chapter 8 for a review of movements possible at synovial joints.

In performing any given movement, such as bending the leg at the knee joint, the muscles performing the actual movement are called the prime movers or agonists. Those muscles that will straighten the knee are the antagonists. The agonist or prime mover must relax for the antagonists to perform their function and vice versa. Synergists (SIN-er-jistz) are the muscles that assist the prime movers.
Agonists are prime movers
Synergists assist the prime movers.

The more fixed attachment of a muscle that serves as a basis for the action is the origin

In performing any given movement, such as bending the leg at the knee joint, the muscles performing the actual movement are called the prime movers or agonists
Skeletal muscles may be named according to their action. Knowing this, do you think the adductor longus muscle would be on the medial or lateral aspect of your thigh? Medial—adduction is the movement of a body part towards midline.
The superficial muscles of the body are those that can be found directly under the skin Some parts of the body, like the arms and legs, will have up to three different layers of muscles (superficial, middle and deep layers). Other areas will have only superficial muscles, like the cranial area of the skull. These muscles can be better seen on a living human who is a bodybuilder or an athlete. These individuals exercise regularly at a gym developing their superficial muscles.
A number of muscles are involved in creating facial expressions and body language. The occipitalis (ok-sip-ih-TAL-is) draws the scalp backward. The frontalis (frohn-TAL-is) raises your eyebrows and wrinkles the skin of your forehead. The zygomaticus (zye-go-MAT-ick-us) muscles are involved in smiling and laughing. The levator labii superioris (leh-VAY-ter LAY-bee-eye soo-peer-ee-OR-is) raises your upper lip. The orbicularis oris (or-BICK-you-lahr-is OR-is) closes your lips and the buccinator (BUCK-sin-aye-tohr) compresses your cheek. These two muscles are involved in puckering up to kiss.
Mastication (mass-tih-KAY-shun) or chewing is caused by some very strong muscles. The table on the next screen lists the muscles of mastication and the functions they perform. The masseter (mass-SEE-ter) and the temporalis (tim-poh-RAL-is) are the main muscles that close your jaw by bringing up the mandibile in a bite grip. They are assisted by the pterygoid (TEHR-ih-goyd) muscles.
The muscles that move the eyes are unique in that they do not insert on bone, instead they insert on the eyeball. The table on the next screen lists the muscles that move the eyes and the functions they perform. The superior rectus raises the eye; the inferior rectus lowers the eye. The medial rectus rolls the eye medially and the lateral rectus rolls the eye laterally. The superior and inferior oblique muscles rotate the eyeball on axis.

The main muscle that moves the head is the sternocleidomastoid (stir-noh-kyle-doh-MASS-toyd) muscle. The table on the next screen lists the muscles of the head and the functions they perform. Contraction of both sternocleidomastoids causes flexion of the neck; contraction of one at a time results in rotation to the left or right. Other muscles of the neck assist the sternocleidomastoid in moving the head.
The muscles that move the scapula are the levator scapulae (leh-VAY-ter SKAP-you-lee), the rhomboids (ROM-boydz), the pectoralis (peck-toh-RAL-is) minor and the trapezius (trah-PEE-zee-us). The trapezius is seen superficially between the neck and the clavicle. Refer to the animation to view superficial anatomy of the muscles of the trunk. The serratus (sir-AYE-tis) anterior muscle looks like the teeth of a saw on the lateral upper side of the trunk. These muscles all move the scapula.
Most of the muscles that move the humerus originate on the bones of the shoulder girdle. The table on the next screen lists the muscles that move the humerus and the functions they perform. The pectoralis major flexes and adducts the arm. The latissimus dorsi (lah-TISS-ih-mus DOR-sigh) muscle extends adducts and rotates the arm medially. Because these movements are used in swimming, this muscle is often called the swimmer’s muscle.
The following muscles are often referred to as the rotator cuff muscles. The teres minor adducts and rotates the arm. The deltoid (DELL-toyd) abducts the arm and is also the muscle that receives injections. The supraspinatus (sue-prah-spye-NAH-tus) also abducts the arm. The infraspinatus (in-frah-spye-NAH-tus) rotates the arm.

Three muscles flex the forearm at the elbow: the brachialis (bray-kee-AL-us), the biceps brachii (BYE-seps BRAY-kee-eye) and the brachioradialis (bray-kee-oh-ray-dee-AH-lus). The table on the next screen lists the muscles that move the elbow and the functions they perform. Two muscles extend the arm: the triceps brachii and the anconeus (an-KOH-nee-us).
The two flexor carpi (FLEKS-ohr KAHR-pye) muscles flex the wrist and the three extensor carpi muscles extend the wrist with the assistance of the extensor digitorum communis. These muscles are also involved in abducting and adducting the wrist. When your pulse is taken, the tendon of the flexor carpi radialis is used as the site to locate the radial pulse.
Supination of the hand so that the palm is facing upward is caused by the supinator (soo-pin-NAY-tohr) muscle. The two muscles that pronate the hand so that the palm faces downward are the pronator teres (pro-NAY-tohr TAYR-eez) and the pronator quadratus (pro-NAY-tohr kwod-RAH-tus). These muscles are found beneath the superficial muscles deep in the arm.
The thumb is capable of movement in many directions, giving the hand a unique capability that separates humans from all other animals. We can grasp and use tools because of our thumb. The two flexor pollicis (FLEKS-ohr pol-ISS-is) muscles flex the thumb, pollicis coming from the Latin for “thumb.” The two extensor pollicis muscles extend the thumb. The adductor pollicis muscle adducts the thumb; the two abductor pollicis muscles abduct the thumb. The unique opponens (oh-POH-nenz) pollicis flexes and opposes the thumb and is used when we write.

The flexor digitorum (FLEKS-ohr dij-ih-TOHR-um) muscles flex the fingers; the extensor digitorum muscle extends the fingers. Refer to the table on the right. The little finger and the index finger have separate similar muscles. The interossei (in-tehr-OSS-eye) muscles, found between the metacarpals, cause abduction of the proximal phalanges of the fingers. The tendons of the extensor digitorum are visible on the surface of your hand. Extend your fingers to view these tendons.
Three layers of muscles along the side of the abdomen constrict and hold the abdominal contents in place. They are from outer to inner: the external oblique, the internal oblique and the transversus abdominis. In the front over your belly is the rectus abdominis. This is the muscle that we develop when we do sit-ups and try to get that “washboard” look. The animation lists the muscles of the abdominal wall and respiration.
The main muscle used in breathing is the diaphragm (DYE-ah-fram). Its contracting causes air to enter the lungs. When it relaxes air is expelled from the lungs. To expand the ribs while the lungs fill with air, the external and internal intercostal muscles come into play. The external intercostals elevate the ribs when we breathe in or inspire, and the internal intercostals depress the ribs when we breathe out or expire.
The psoas (SO-us) muscles and the iliacus (ill-ee-ACK-us) muscle flex the thigh. Three gluteal muscles form the buttocks: the gluteus (GLOO-tee-us) maximus forms most of the buttocks; the gluteus medius, where injections are administered, is above and lateral to the maximus; and the gluteus minimus. The gluteus maximus extends the thigh. There are two adductor muscles and one abductor. The tensor fascia lata (TIN-sir FASH-ee-ah LAH-tuh) tenses the fascia lata, which is a thick band of connective tissue on the lateral side of the thigh causing abduction of the femur.
Six muscles involved in flexion of the knee are found posteriorly on the thigh and four muscles involved in extension are found on the anterior surface of the thigh. The table on the next screen lists the muscles involved in flexion of the knee. The flexors of the knee are the biceps femoris (BYE-seps FEM-ohr-iss), the semitendinosus (sim-ee-tin-dih-NO-sus), the semimembranosus (sim-ee-mim-brah-NO-sus) (these first three are also known as the hamstrings), the popliteus (pop-lih-TEE-us), the gracilis (GRASS-ih-liss) and the sartorius (sahr-TOHR-ee-us).
The quadriceps femoris muscle consists of four parts that extend the knee. They are the rectus femoris, the vastus lateralis, the vastus medialis and the vastus intermedius. The vastus medialis and vastus lateralis are easily seen superficially on the anterior thigh. The sartorius muscle is the longest muscle of the body and is known as the “tailors” muscle. It flexes the thigh and leg and rotates the thigh laterally for sitting cross-legged, a position some tailors sit in while sewing.
The hamstrings get their name because the tendons of these muscles in hogs or pigs were used to suspend the hams during curing or smoking. Many predators bring down their prey by biting through these hamstrings. When persons “pull a hamstring,” they have torn the tendons of one of these muscles.

Five muscles plantar flex the foot or bring it downward. They are the gastrocnemius (gas-trok-NEE-mee-us) or calf muscle, the tibialis posterior, the soleus (SO-lee-us), the peroneus (payr-oh-NEE-us) longus and the plantaris (plan-TAH-ris). Two muscles dorsally flex the foot or bring it upward. They are the tibialis anterior and the peroneus tertius. The table on the right lists the muscles involved in moving the foot.

Two muscles flex the great toe: the flexor hallucis (FLEKS-ohr HAL-uh-kiss) brevis and longus; one muscle extends the great toe, the extensor hallucis. The flexor digitorum muscles flex the toes while the extensor digitorum extends the toes. The abductor hallucis abducts the great toe and the abductor digiti minimi abducts the little toe. A total of 20 intrinsic muscles of the foot move the toes to flex, extend, adduct and abduct. The table on the right lists the muscles involved in moving the toes.
The superior rectus muscle raises the eye, while the inferior rectus muscle lowers the eye.
The main muscles that close your jaw by bringing up the mandible in a bite grip are the masseter and the temporalis
To expand the ribs while the lungs fill with air, the external and internal intercostal muscles come into play.
Chewing, made possible by the masseter and temporalis muscles which close the jaw by bringing up the mandible in a bite grip, is also called mastication
The muscle that raises the eyebrows and wrinkles the skin of the forehead is the frontalis muscle.
After studying for hours, Laura’s shoulders are very stiff and sore. Alan, her boyfriend, reaches over to rub her shoulders. What muscle primarily will he be massaging? Trapezius
Integumentary System 1. Sensory receptors in the skin stimulate muscle contraction in response to environmental changes in temperature or pressure. 2. Skin dissipates heat during muscle contraction.

Skeletal System 1. Bones provide attachments for muscles and act as levers to bring about movement. 2. Bones store calcium necessary for muscular contraction.

Nervous System 1. Motor neurons stimulate muscle contraction by releasing acetylcholine at their axon terminals in the neuromuscular junction.

Endocrine System 1. Growth hormone from the anterior pituitary gland stimulates muscular development. 2. Hormones increase blood flow to muscles during exercise.

Cardiovascular System 1. The heart pumps blood to the muscle cells, carrying nutrients to and wastes away from the muscle cells. 2. Red blood cells carry oxygen to and carbon dioxide gas away from the muscle cells.

Lymphatic System 1. Skeletal muscle contractions push lymph through the lymphatic vessels, particularly by the action of breathing. 2. Lymphocytes combat infection in the muscles and develop immunities.

Digestive System 1. Skeletal muscle contraction in swallowing brings food to the system; smooth muscle contraction pushes digested food through the stomach and intestines. 2. The intestines absorb digested nutrients to make them available to muscle cells for their energy source.

Respiratory System 1. Breathing depends on the diaphragm and intercostal muscles. 2. The lungs provide oxygen for muscle cells and eliminate the carbon dioxide waste from cellular respiration.

Urinary System 1. Smooth muscles push urine from the kidneys down the ureters to the bladder. 2. Skeletal muscles control urine elimination. 3. In the loop of Henle in the nephrons of the kidneys, calcium levels are controlled by eliminating any excess or restoring needed calcium to the blood for muscle contraction.

Reproductive System 1. Skeletal muscles are involved in kissing, erections, transferring sperm from the male to the female and other forms of sexual behavior and activity. 2. Smooth muscle contractions in the uterus bring about delivery of the newborn.
CHAPTER 10
The nervous system can be grouped into two major categories: 1. Central Nervous System (CNS) 2. Peripheral Nervous System (PNS)
The first is the central nervous system (CNS), which is the control center for the whole system. It consists of the brain and spinal cord. All body sensations and changes in our external environment must be relayed from receptors and sense organs to the CNS to be interpreted (what do they mean) and then, if necessary, acted on (such as move away from a source of pain or danger)

The second major category is the peripheral nervous system (PNS), which is subdivided into several smaller units. This second category consists of all the nerves that connect the brain and spinal cord with sensory receptors, muscles and glands.

The PNS can be divided into two subcategories: 1. the afferent peripheral system, which consists of afferent or sensory neurons that convey information from receptors in the periphery of the body to the brain and spinal cord 2. the efferent peripheral system, which consists of efferent or motor neurons that convey information from the brain and spinal cord to muscles and glands.
The efferent peripheral system can be further subdivided into two subcategories. 1. The first is the somatic nervous system, which conducts impulses from the brain and spinal cord to skeletal muscle, thereby causing us to respond or react to changes in our external environment. 2. The second is the autonomic nervous system (ANS), which conducts impulses from the brain and spinal cord to smooth muscle tissue (like the smooth muscles of the intestine that push food through the digestive tract), to cardiac muscle tissue of the heart and to glands (like the endocrine glands).
The ANS is considered to be involuntary. The organs affected by this system receive nerve fibers from two divisions of the ANS: 1. the sympathetic division, which stimulates or speeds up activity and thus involves energy expenditure and uses norepinephrine (nor-ep-ih-NEH-frin) as a neurotransmitter, and 2. the parasympathetic division, which stimulates or speeds up the body’s vegetative activities such as digestion, urination and defecation and restores or slows down other activities. It uses acetylcholine (ah-seh-till-KOH-leen) as a neurotransmitter at nerve endings.
Being a control center and a communication network is a function of the nervous system.
The control center for the entire system is the central nervous system
Motor neurons are part of the efferent nervous system
The speeding up of activity is a function of the Sympathetic division of the ANS
The parasympathetic division stimulates the body’s vegetative activities and slows down other activities.

The Somatic nervous system conducts impulses from the brain and spinal cord to skeletal muscle, thereby causing us to respond or react to changes in our external environment.

The body's control center and communication network, which directs the functions of the body's organs and systems, is the nervous system

The second major category of the nervous system consisting of all the nerves that connect the brain and spinal cord with sensory receptors, muscles, and glands is the peripheral nervous system

Nervous tissue consists of groupings of nerve cells or neurons(NOO-ronz) that transmit information called nerve impulses in the form of electrochemical changes. A nerve is a bundle of nerve cells or fibers. Nervous tissue is also composed of cells that perform support and protection. These cells are called neuroglia(noo-ROWG-lee-ah) or glial (GLEE-al) cells (neuroglia means nerve glue). Over 60% of all brain cells are neuroglia cells.

There are different kinds of neuroglial cells, and, unlike neurons, they do not conduct impulses. The table on the right lists the types of neuroglia.

Astrocytes are star-shaped cells that wrap around nerve cells to form a supporting network in the brain and spinal cord. They attach neurons to their blood vessels, thus helping regulate nutrients and ions that are needed by the nerve cells.

Oligodendroglia (all-ih-goh-DEN-droh-GLEE-ah) look like small astrocytes. They also provide support by forming semi rigid connective-like tissue rows between neurons in the brain and spinal cord. They produce the fatty myelin (MY-eh-lin) sheath on the neurons of the brain and spinal cord of the CNS.

Microglial (my-KROWG-lee-al) cells are small cells that protect the CNS and whose role is to engulf and destroy microbes like bacteria and cellular debris.

Ependymal (eh-PIN-dih-mal) cells line the fluid-filled ventricles of the brain. Some produce cerebrospinal fluid and others with cilia move the fluid through the CNS.

Schwann cells form myelin sheaths around nerve fibers in the PNS.

Each nerve cell’s body contains a single nucleus. This nucleus is the control center of the cell. In the cytoplasm there are mitochondria, Golgi bodies, lysosomes and a network of threads called neurofibrils that extend into the axon part of the cell, referred to as the fiber of the cell. In the cytoplasm of the cell body there is extensive rough endoplasmic reticulum (ER). In a neuron, the rough ER has ribosomes attached to it. These granular structures are referred to as Nissl (NISS-l) bodies, also called chromatophilic substance, and are where protein synthesis occurs.

* There are two kinds of nerve fibers on the nerve cell: * dendrites (DEN-drightz) * axons
Dendrites are short and branched, like the branches of trees. These are the receptive areas of the neuron and a multipolar neuron will have many dendrites.

A nerve cell, however, will have only one axon, which begins as a slight enlargement of the cell body called the axonal hillock. The axon is a long process or fiber that begins singly but may branch and at its end has many fine extensions called axon terminals that contact with dendrites of other neurons. Numerous mitochondria and neurofibrils are in the axon.

The large peripheral axons are enclosed in fatty myelin sheaths produced by the Schwann cells. These are a type of neuroglial cell that wrap tightly in layers around the axon, producing fatty sheets of lipoprotein. The portions of the Schwann cell that contain most of the cytoplasm of the cell and the nucleus remain outside of the myelin sheath and make up a portion called the neurilemma. Narrow gaps in the sheath are the nodes of Ranvier.

Cells that conduct impulses from one part of the body to another are called neurons. They may be classified by both function and structure. The structural classification consists of three types of cells. 1. Multipolar 2. Bipolar 3. Unipolar
Multipolar neurons are neurons that have several (multi) dendrites and one axon. Most neurons in the brain and spinal cord are this type. The neuron studied in Chapter 5 is this type. Recall that the part of the neuron with the nucleus is called the cell body. The smaller extensions of the cell body are the dendrites, and the single long extension is called the axon.

Single cells called Schwann cells, also called neurolemmocytes (noo-row-leh-MOH-sights), surround the axon at specific sites and form the fatty myelin sheath around the axons in the peripheral nervous system.

Gaps in the myelin sheath are called nodes of Ranvier (NOHDZ of rahn-vee-A), also called neurofibral nodes. These gaps allow ions to flow freely from the extracellular fluids to the axons, assisting in developing action potentials for nerve transmission.

Bipolar neurons have one dendrite and one axon. They function as receptor cells in special sense organs. Only two (bi) processes come off the cell body. They are found in only three areas of the body: the retina of the eye, the inner ear and the olfactory area of the nose.

Unipolar neurons have only one process extending from the cell body. This single process then branches into a central branch that functions as an axon and a peripheral branch that functions as a dendrite. Most sensory neurons are unipolar neurons. The branch functioning as an axon enters the brain or spinal cord; the branch functioning as a dendrite connects to a peripheral part of the body.

Nerve cells pick up various changes in the environment (stimuli such as changes in temperature or pressure) from receptors. Receptors are the peripheral nerve endings of sensory nerves that respond to stimuli. There are many different types of receptors. Our skin has an enormous number of such receptors. These receptors change the energy of a stimulus, like heat, into nerve impulses. The first nerve cell receiving this impulse directly from a receptor is called a sensory or afferent neuron. These neurons are of the unipolar type. The receptors are in contact with only one end of the sensory neuron (the peripheral process in the skin), thus ensuring a one-way transmission of the impulse. The central process of the sensory neuron goes to the spinal cord.

From the sensory neuron, the impulse may pass through a number of internuncial or association neurons. These are found in the brain and the spinal cord and are of the multipolar type. They transmit the sensory impulse to the appropriate part of the brain or spinal cord for interpretation and processing.

From the association or internuncial neurons, the impulse is passed to the final nerve cell, the motor or efferent neuron. The motor neuron is of the multipolar type. This neuron brings about the reaction to the original stimulus. It is usually muscular (like pulling away from a source of heat or pain) but it can also be glandular (like salivating after smelling freshly baked cookies).

A nerve is a bundle of neurons

The nerve glue is the neuroglial cell.

The nerve fibers on the nerve cell that are the receptive areas of the neuron are known as: dendrites

Star-shaped cells that twine around neurons for support in the brain and spinal cord and connect neurons to blood vessels are known as astrocytes

Small cells that engulf and destroy microbes and cellular debris to protect the central nervous system are called microglia

A nerve cell is similar to a muscle cell in that there are concentrations of ions on the inside and the outside of the cell membrane. Positively charged sodium (Na1) ions are in greater concentration outside the cell than inside. There is a greater concentration of positively charged potassium (K1) ions inside the cell than outside. This situation is maintained by the cell membrane’s sodium-potassium pump. In addition to the potassium ion, the inside of the fiber has negatively charged chloride (Cl2) ions and other negatively charged organic molecules.

Thus, the nerve fiber has an electrical distribution as well, such that the outside is positively charged while the inside is negatively charged. This condition is known as the membrane or resting potential. Na1 and K1 ions tend to diffuse across the membrane but the cell maintains the resting potential through the channels of the sodium-potassium pump that actively extrudes Na1 and accumulates K1 ions.

When a nerve impulse begins, the permeability to the sodium (Na1) ions changes; Na1 rushes in, causing a change from a negative (-) to a positive (+) charge inside the nerve membrane. This reversal of electrical charge is called depolarization and creates the cell’s action potential. The action potential moves in one direction down the nerve fiber.

Now the potassium ions begin to move outside to restore the resting membrane potential. The sodium-potassium pump begins to function, pumping out the sodium ions that rushed in and pulling back in the potassium ions that moved outside, thus restoring the original charges. This is called repolarization, as shown in figure on the right, and the inside of the cell again becomes negative. This process continues along the nerve fiber acting like an electrical current, carrying the nerve impulse along the fiber. The nerve impulse is a self-propagating wave of depolarization followed by repolarization moving down the nerve fiber.

An unmyelinated nerve fiber conducts an impulse over its entire length, but the conduction is slower than that along a myelinated fiber. A myelinated fiber is insulated by the myelin sheath, so transmission occurs only at the nodes of Ranvier between adjacent Schwann cells. Action potentials and inflow of ions occur only at these nodes, allowing the nerve impulse to jump from node to node, and the impulse travels much faster. An impulse on a myelinated motor fiber going to a skeletal muscle could travel about 120 meters per second, while an impulse on an unmyelinated fiber would travel only 0.5 meter per second.

On any nerve fiber, the impulse will never vary in strength. If the stimulus or change in the environment is barely great enough to cause the fiber to carry the impulse, the impulse will be the same strength as one excited by a stronger stimulus. This is known as the all-or-none law, which states that if a nerve fiber carries any impulse, it will carry a full strength impulse.

The three types of ions involved in nerve impulses are potassium (K), sodium (Na) and chloride (Cl).

Reversal of electrical charge is depolarization

When the outside of a nerve is positively charged and the inside is negatively charged, the condition is known as the Resting potential

Synapses (sin-AP-seez) are the areas where the terminal branches of an axon (the axon terminals) are anchored close to, but not touching, the ends of the dendrites of another neuron. These synapses are one-way junctions that ensure that the nerve impulse travels in only one direction. This area is called a synaptic cleft. Other such areas of synapses are between axon endings and muscles or between axon endings and glands. An impulse continuing along a nerve pathway must cross this gap.

Transmission across synapses is brought about by the secretions of very low concentrations of chemicals called neurotransmitters that move across the gap. As the nerve impulse travels down the fiber, it causes vesicles in the axon endings of a presynaptic neuron to release the chemical neurotransmitter. Most of the synapses in our bodies use acetylcholine as the neurotransmitter. The acetylcholine allows the impulse to travel across the synaptic cleft to the postsynaptic neuron. However, it does not remain there because an enzyme in the cleft, acetylcholinesterase, immediately begins to break down the acetylcholine after it performs its function.

The autonomic nervous system uses adrenaline (also called epinephrine) as the transmitting agent. Many kinds of neurotransmitters are found in the nervous system. Some neurons produce only one type, others produce two or three. The best known neurotransmitters are acetylcholine and norepinephrine. Some others are serotonin (sayr-oh-TOH-nin), dopamine (DOH-pah-meen) and the endorphins (in-DOHR-finz).

Transmission of nerve impulses across synapses is brought about by the secretion of very low concentrations of chemicals called Neurotransmitters, which move across the gap.

The areas where the terminal branches of an axon are anchored close to, but not touching, the ends of the dendrites of another neuron are known as synapses.

When we have an involuntary reaction to an external stimulus, we experience what is called a reflex. This is experienced when we prick our finger on a rose thorn and immediately pull away from the source of pain. The reflex allowed us to respond much more quickly than if we had to consciously think about what to do and interpret the information in the CNS. A reflex then is an involuntary reaction or response to a stimulus applied to our periphery and transmitted to the CNS.

A reflex arc is the pathway that results in a reflex. It is a basic unit of the nervous system and is the smallest and simplest pathway able to receive a stimulus, enter the CNS (usually the spinal cord) for immediate interpretation and produce a response.

The reflex arc has five components: 1. a sensory receptor in the skin 2. a sensory or afferent neuron 3. association or internuncial neurons within the spinal cord 4. a motor or efferent neuron 5. an effector organ like a muscle.
You have probably experienced a reflex arc when you had a physical examination and the doctor hit below your knee with a rubber mallet. This is the knee-jerk reflex, also called the patellar tendon reflex. The doctor hits the patellar tendon just below the patella (the stimulus), causing the stimulation of stretch receptors within the quadriceps femoris muscle. They send the impulse via sensory neurons to the spinal cord for interpretation. The impulse then travels to a motor neuron (response) back to the muscles that contract and your leg extends.

Reflexes also occur within our bodies to help maintain homeostasis. Heartbeat rate, digestion and breathing rates are controlled and maintained by reflexes concerned with involuntary processes. Coughing (the choke reflex), sneezing, swallowing and vomiting are other examples of automatic subconscious reactions to changes within or outside our body.

A reflex arc is the simplest pathway able to receive a stimulus, enter the central nervous system for immediate interpretation, and produce a response.

An involuntary reaction to an external stimulus is known as a (n) reflex

During a routine checkup, Carlos is intrigued when the nurse practitioner taps his knee with a rubber hammer and his leg moves. What is being tested? How does the information travel from Carlos’ knee to the contracting muscle? His patellar reflex is being tested. Information travels from his knee along a sensory neuron to the spinal cord and then from the spinal cord to his muscle along a motor neuron.

In the nervous system, a number of terms are used to describe nervous tissue organization. It is important to understand the meanings of these terms.

The term white matter refers to groups of myelinated axons (myelin has a whitish color) from many neurons supported by neuroglia. White matter forms nerve tracts in the CNS.

The gray areas of the nervous system are called gray matter, consisting of nerve cell bodies and dendrites. It also can consist of bundles of unmyelinated axons and their neuroglia. The gray matter on the surface of the brain is called the cortex.

A nerve is a bundle of fibers located outside the CNS. Most nerves are white matter. Nerve cell bodies that are found outside the CNS are generally grouped together to form ganglia (GANG-lee-ah). Because ganglia are made up primarily of unmyelinated nerve cell bodies, they are masses of gray matter.

A tract is a bundle of fibers inside the CNS. Tracts can run long distances up and down the spinal cord. Tracts are also found in the brain and connect parts of the brain with each other and parts of the brain with the spinal cord. Ascending tracts conduct impulses up the cord and are concerned with sensation. Descending tracts conduct impulses down the cord and are concerned with motor functions. Tracts are made of myelinated fibers and therefore are classified as white matter.
Two other terms are of note: a nucleus is a mass of nerve cell bodies and dendrites inside the CNS, consisting of gray matter; horns are the areas of gray matter in the spinal cord.

The gray matter on the brain’s surface is known as the cortex

A bundle of nerve fibers located inside the central nervous system is known as a tract

An area of gray matter in the spinal cord is known as a horn

The spinal cord begins as a continuation of the medulla oblongata of the brainstem. Its length is approximately 16 to 18 inches. Its diameter varies at different levels because it is surrounded and protected by bone (the vertebrae) and by disks of fibrocartilage (the intervertebral disks). It is made up of a series of 31 segments, each giving rise to a pair of spinal nerves. In addition to the above protection, the spinal cord (as well as the brain) is further protected by the meninges (men-IN-jeez), a series of connective tissue membranes. Those associated specifically with the spinal cord are called the spinal meninges.

The outermost spinal meninx is called the dura mater (DOO-rah-MATE-ehr), which means tough mother. It forms a tough outer tube of white fibrous connective tissue.

The middle spinal meninx is called the arachnoid mater (ah-RACK-noyd MATE-ehr) or spider layer. It forms a delicate connective membranous tube inside the dura mater.

The innermost spinal meninx is known as the pia mater (PEE-ah MATE-ehr) or delicate mother. It is a transparent fibrous membrane that forms a tube around and adheres to the surface of the spinal cord (and brain). It contains numerous blood vessels and nerves that nourish the underlying cells.

Between the dura matter and the arachnoid is a space called the subdural space, which contains serous fluid. Between the arachnoid and the pia mater is the subarachnoid space. It is here that the clear, watery cerebrospinal fluid circulates. The meninges do not attach directly to the vertebrae. They are separated by a space called the epidural space. This space contains loose connective tissue and some adipose tissue that acts as a protective cushion around the spinal cord.

A major function of the spinal cord is to convey sensory impulses from the periphery to the brain and to conduct motor impulses from the brain to the periphery. Ascending nerve tracts of the spinal cord carry sensory information from body parts to the brain, and descending tracts conduct motor impulses from the brain to muscles and glands.

A second principal function is to provide a means of integrating reflexes. A pair of spinal nerves is connected to each segment of the spinal cord. Each pair of spinal nerves is connected to that segment of the cord by two pairs of attachments called roots. The posterior or dorsal root is the sensory root and contains only sensory nerve fibers. It conducts impulses from the periphery (like the skin) to the spinal cord. These fibers extend into the posterior or dorsal gray horn of the spinal cord.

The other point of attachment of the spinal nerve to the cord is the anterior or ventral root and this is the motor root. It contains motor nerve fibers only and conducts impulses from the spinal cord to the periphery (like muscles). It connects with the anterior or ventral gray horn of the spinal cord.

The 31 pairs of spinal nerves arise from the union of the dorsal and ventral roots of the spinal nerves. All the spinal nerves are mixed nerves because they consist of both motor and sensory fibers. Most of the spinal nerves exit the vertebral column between adjacent vertebrae. They are named and numbered according to the region and level of the spinal cord from which they emerge.

There are 8 pairs of cervical nerves, 12 pairs of thoracic nerves, 5 pairs of lumbar nerves, 5 pairs of sacral nerves and a single pair of coccygeal nerves.

The spinal nerves are also numbered according to the order (starting superiorly) within the region. Thus, the 31 pairs are: 1. C1 through C8 (cervical) 2. T1 through T12 (thoracic) 3. L1 through L5 (lumbar) 4. S1 through S5 (sacral) 5. Cx (coccygeal)
The sensory root of the spinal cord is the dorsal or posterior root

There are Eight pairs of cervical nerves.

The dura mater, which means "tough mother," is the outermost layer of the meninges.

The middle layer, or "spider layer," of the meninges is called the arachnoid mater.

The transparent fibrous membrane that forms a tube around and adheres to the surface of the spinal cord and brain is called the pia mater.

Nerve tracts of the spinal cord that carry sensory information from body parts to the brain are known as which type of nerve tract? Ascending

Nerve tracts of the spinal cord that conduct motor impulses from the brain to the muscles and glands are known as which type of nerve tract? Descending

Talia was in a car accident and damaged the anterior portion of her spinal cord. Which function is more likely to be affected-sensory or motor? Motor

Isabel’s one-year-old daughter has been running a high fever and is crying constantly. Her doctor suspects meningitis and wants to perform a spinal tap. What exactly is a spinal tap? Where will the needle be inserted? A spinal tap is a procedure done to sample cerebrospinal fluid in the subarachnoid space along the spinal column. The needle is usually inserted in the lumbar region to avoid hitting the spinal cord.

Isabel’s one-year-old daughter has been running a high fever and is crying constantly. Her doctor suspects meningitis and wants to perform a spinal tap. What exactly is a spinal tap? Where will the needle be inserted
CHAPTER 11
The brain is divided into four main parts: 1. The brainstem controls breathing, heartbeat rates and reactions to visual and auditory stimuli. 2. The diencephalon includes the thalamus and the hypothalamus, which controls many functions, including those related to homeostasis. 3. The cerebrum controls intellectual processes and emotions, while the cerebellum maintains body posture and balance. 4. The autonomic nervous system controls all the involuntary functions of the body such as regulating our internal organs and controlling glands. The special senses are part of the nervous system and include sight, hearing and balance, smell and taste.
The brain is one of the largest organs of the body. It weighs about 3 pounds in an average adult. It is divided into four major parts: 1. the brainstem, which consists of three smaller areas, the medulla oblongata (meh-DULL-ah ob-long-GAH-tah), the pons varolii (PONZ-vah-ROH-lee-eye) and the midbrain; 2. the diencephalon, (dye-en-SEFF-ah-lon), consisting of the thalamus (THAL-ah-muss) and the hypothalamus; 3. the cerebrum (seh-REE-brum); and the cerebellum (seh-ree-BELL-um).
The brain is protected by the cranial bones and the meninges. The cranial meninges is the name given to the meninges that protect the brain, and they have the same structure as the spinal meninges: the outer dura mater, the middle arachnoid mater and the inner pia mater (discussed in Chapter 10). The brain, like the spinal cord, is further protected by the cerebrospinal fluid that circulates through the subarachnoid space around the brain and spinal cord and through the ventricles of the brain. The ventricles are cavities within the brain that connect with each other, with the subarachnoid space of the meninges and with the central canal of the spinal cord. The cerebrospinal fluid serves as a shock absorber for the central nervous system and circulates nutrients.
The brain has four ventricles. There are two lateral ventricles in each side or hemisphere of the cerebrum under the corpus callosum (KOR-pus kah-LOH-sum). The third ventricle is a slit between and inferior to the right and left halves of the thalamus, and situated between the lateral ventricles. Each lateral ventricle connects with the third ventricle by a narrow oval opening called the interventricular foramen or foramen of Monroe.
The fourth ventricle lies between the cerebellum and the lower brainstem. It connects with the third ventricle via the cerebral aqueduct also known as the aqueduct of Sylvius. The roof of this fourth ventricle has three openings through which it connects with the subarachnoid space of the brain and spinal meninges, thus allowing a flow of cerebrospinal fluid through the spinal cord, the brain and the ventricles of the brain.
The brain is protected by the cranial bones and the meninges.
The brain weighs about 3 pounds
The three cranial meninges are the outer dura mater, the middle arachnoid mater and the inner pia mater.
The third and fourth ventricles are connected by the cerebral aqueduct
Cavities within the brain that connect with each other, with the subarachnoid space of the meninges, and with the central canal of the spinal cord are known as ventricles

The brainstem consists of the medulla oblongata, the pons varolii and the midbrain. It connects the brain to the spinal cord. It is a very delicate area of the brain because damage to even small areas could result in death. The figure to the right shows the parts of the brain and areas of brain function.
The medulla oblongata contains all the ascending and descending tracts that connect between the spinal cord and various parts of the brain. These tracts make up the white matter of the medulla. Some motor tracts cross as they pass through the medulla. The crossing of the tracts is called decussation of pyramids and explains why motor areas on one side of the cortex of the cerebrum control skeletal muscle movements on the opposite side of the body.
The medulla also contains an area of dispersed gray matter containing some white fibers. This area is called the reticular formation, which functions in maintaining consciousness and arousal. Within the medulla are three vital reflex centers of this reticular system: the vasomotor center, which regulates the diameter of blood vessels; the cardiac center, which regulates the force of contraction and heartbeat; and the medullary rhythmicity area, which adjusts your basic rhythm of breathing.
The pons varolii is a bridge (pons is Latin for “bridge”) that connects the spinal cord with the brain and parts of the brain with each other. Longitudinal fibers connect with the spinal cord or medulla with the upper parts of the brain, and transverse fibers connect with the cerebellum. Its pneumotaxic and apneustic area help control breathing.
The midbrain, also called the mesencephalon (mess-in-SEFF-ah-lon), contains the ventral cerebral peduncles (seh-REE-bral peh-DUN-kullz) that convey impulses from the cerebral cortex to the pons and spinal cord. It also contains the dorsal tectum, which is a reflex center that controls the movement of the eyeballs and head in response to visual stimuli; it also controls the movement of the head and trunk in response to auditory stimuli, such as loud noises.
The area contained within the medulla having dispersed gray matter is the reticular formation
The midbrain contains the ventral cerebral peduncles
Sylvia is babysitting her little brother, who always seems to have his head in a book. Finally, after the third time asking a question and getting no reply, she says “Do you have a hole in your head or what?” “Actually,” he replies, “I have four. They’re called ventricles.” What are these ventricles and where would you find them?
Ventricles are cavities within the brain. They connect with each other and with the subarachnoid space and central canal. Cerebrospinal fluid is created in and flows through the ventricles. Two lateral ventricles are under the corpus callosum on either side. The third ventricle is a narrow opening between the halves of the thalamus. The fourth ventricle is between the cerebellum and lower brainstem.
The diencephalon is superior to the midbrain and between the two cerebral hemispheres. It also surrounds the third ventricle. It is divided into two main areas: the thalamus and the hypothalamus. It also contains the optic tracts and optic chiasma where optic nerves cross each other; the infundibulum, which attaches to the pituitary gland; the mamillary bodies, which are involved in memory and emotional responses to odor; and the pineal (PIN-ee-al) gland, which is part of the epithalamus. The pineal gland is a pinecone-shaped endocrine gland that secretes melatonin, which affects our moods and behavior. This is discussed further in Chapter 12.
The thalamus is the superior part of the diencephalon and the principal relay station for sensory impulses that reach the cerebral cortex coming from the spinal cord, brainstem and parts of the cerebrum. It also plays an important role as an interpretation center for conscious recognition of pain and temperature and for some awareness of crude pressure and touch.
The epithalamus is a small area superior and posterior to the thalamus. It contains some small nuclei that are concerned with emotional and visceral responses to odor. It contains the pineal gland.
The hypothalamus is the inferior part of the diencephalon and, despite its small size, controls many bodily functions related to homeostasis. It controls and integrates the autonomic nervous system. It receives sensory impulses from the internal organs. It is the intermediary between the nervous system and the endocrine system because it sends signals and controls the pituitary gland.
It is the center for mind-over-body phenomena. When we hear of unexplainable cures in people diagnosed with terminal illness but who refused to accept the diagnosis and recovered, the hypothalamus may have been involved in this mind controlling the body phenomenon. It is the hypothalamus that controls our feelings of rage and aggression. It controls our normal body temperature. It contains our thirst center, informing us of when and how much water we need to sustain our bodies. It maintains our waking state and sleep patterns, allowing us to adjust to different work shifts or jetlag travel problems within a day or so. It also regulates our food intake.
The cerebrum makes up the bulk of the brain. Its surface is composed of gray matter and is referred to as the cerebral cortex. Beneath the cortex lies the cerebral white matter. A prominent fissure, the longitudinal fissure, separates the cerebrum into right and left halves or cerebral hemispheres. On the surface of each hemisphere are numerous folds called gyri (JYE-rye) with intervening grooves called sulci (SULL-sigh). The folds increase the surface area of the cortex, which has motor areas for controlling muscular movements, sensory areas for interpreting sensory impulses and association areas concerned with emotional and intellectual processes. A deep bridge of nerve fiber known as the corpus callosum connects the two cerebral hemispheres.
The lobes of the cerebral hemispheres are named after the bones of the skull that lie on top of them: 1. Frontal lobe 2. Parietal lobe 3. Temporal lobe 4. Occipital Lobe 5. Insula
The frontal lobe forms the anterior portion of each hemisphere. It controls voluntary muscular functions, moods, aggression, smell reception and motivation.
The parietal lobe is behind the frontal lobe and is separated from it by the central sulcus. It is the control center for evaluating sensory information of touch, pain, balance, taste and temperature.
The temporal lobe is beneath the frontal and parietal lobes and is separated from them by the lateral fissure. It evaluates hearing input and smell as well as being involved with memory processes. It also functions as an important center for abstract thoughts and judgment decisions.
The occipital lobe forms the back portion of each hemisphere; its boundaries are not distinct from the other lobes. It functions in receiving and interpreting visual input.
A fifth lobe, the insula, is embedded deep in the lateral sulcus. The central sulcus separates the frontal and parietal lobes. The lateral sulcus separates the cerebrum into frontal, parietal and temporal lobes.
The cerebellum is the second largest portion of the brain. It is shaped somewhat like a butterfly. It is located beneath the occipital lobes of the cerebrum and behind the pons and the medulla oblongata of the brainstem. It consists of two partially separated hemispheres connected by a centrally constricted structure called the vermis.
The cerebellum is made up primarily of white matter with a thin layer of gray matter on its surface called the cerebellar cortex. It functions as a reflex center in coordinating complex skeletal muscular movements, maintaining proper body posture and keeping the body balanced. If damaged, there can be a decrease in muscle tone, tremors, a loss of equilibrium and difficulty in skeletal muscle movements.
The diencephalon is divided into a superior part, the thalamus, and an inferior part, the hypothalamus.
The optic tracts and optic chiasma are within the Diencephalon.
The mamillary bodies are involved in memory and emotional response.
The superior part of the diencephalon that plays a role in conscious recognition of pain is the Thalamus.
The surface of the cerebrum made up of gray matter is known as the cerebral cortex.
The Parietal lobe is behind the frontal lobe.
The insula is located deep within the lateral sulcus.
The elevations or folds on the surface of the cerebrum are called gyri.
A prominent fissure that separates the cerebrum into right and left halves or hemispheres is known as the longitudinal fissure.
The autonomic nervous system is a subdivision of the efferent peripheral nervous system. It functions automatically without conscious effort. It regulates the functions of internal organs by controlling glands, smooth muscles and cardiac muscle. It assists in maintaining homeostasis by regulating heartbeat and blood pressure, breathing and body temperature. This system helps us to deal with emergency situations, emotions and physical act
Receptors within organs send sensory impulses to the brain and spinal cord. Motor impulses travel along peripheral nerve fibers that lead to ganglia outside the central nervous system within cranial and spinal nerves. These ganglia are part of the autonomic nervous system.
There are two parts to the autonomic nervous system: 1. Sympathetic division 2. Parasympathetic division
The sympathetic division prepares the body for stressful situations that require energy expenditure, such as increasing heartbeat and breathing rates to flee from a threatening situation. The fibers of the system arise from the thoracic and lumbar regions of the spinal cord. Their axons leave the cord through the ventral roots of the spinal nerves but then leave the spinal nerve and enter members of a chain of paravertebral ganglia extending longitudinally along the side of the vertebral column. Leaving the paravertebral ganglion, another neuron, the postganglionic fiber, goes to the effector organ. The sympathetic division uses acetylcholine in the preganglionic synapses as a neurotransmitter but uses norepinephrine (or noradrenalin) at the synapses of the postganglionic fibers.
The parasympathetic division operates under normal non-stressful conditions. It also functions in restoring the body to a restful state after a stressful experience, thus counterbalancing the effects of the sympathetic division. The preganglionic fibers of the parasympathetic division arise from the brainstem and the sacral region of the spinal cord. They lead outward in the cranial and sacral nerves to ganglia located close to the viscera. The postganglionic fibers are short and go to the muscles or glands within the viscera to bring about their effects. The preganglionic and the postganglionic fibers of the parasympathetic division use acetylcholine as the neurotransmitter into the synapses.
Most organs that receive autonomic motor neurons are innervated by both the parasympathetic and sympathetic divisions. However, there are some exceptions: blood vessels and sweat glands are innervated by sympathetic neurons, and smooth muscles associated with the lens of the eye are controlled by parasympathetic neurons.
The sympathetic division prepares us for physical activity by increasing blood pressure and heartbeat rate, it dilates respiratory passageways for increased breathing rates and it stimulates sweating. It also causes the release of glucose from the liver as a quick source of energy while inhibiting digestive activities. This system is occasionally called the fight or flight system because it prepares us to face a threat or flee quickly from it.
The parasympathetic division stimulates digestion, urination and defecation. It also counteracts the effects of the sympathetic division by slowing down heartbeat rate, lowering blood pressure and slowing the breathing rate. It is also responsible for the constriction of the pupil of the eye. This division is occasionally called the rest and repose system.
The autonomic nervous system, a subdivision of the peripheral nervous system, has two parts; they are the sympathetic, which operates under stressful situations, and the parasympathetic, which operates under normal non-stressful situations.
The Sympathetic division of the nervous system prepares the body for stressful situations that require energy expenditure, such as increasing heartbeat and breathing rates.
Erin is a passenger on a small airplane going through severe turbulence. Suddenly she hears a loud explosion and sees flames outside the window. The pilot quickly announces that they are trying to make an emergency landing. The flight attendant rapidly reviews crash landing procedures. Erin’s sympathetic nervous system has taken full control. What is happening to her heart rate and her respiratory rate? What about the food that she just ate? Erin’s heart rate and respiratory rate will increase in response to the stress. The sympathetic nervous system will also inhibit digestion.
There are 12 pairs of cranial nerves. Ten pairs originate from the brainstem. All 12 pairs leave the skull through various foramina of the skull. They are designated in two ways: by Roman numerals indicating the order in which the nerves arise from the brain (from the front of the brain to the back) and by names that indicate their function or distribution. Some cranial nerves are only sensory or afferent; others are only motor or efferent. Cranial nerves with both sensory and motor functions are called mixed nerves. 1. The olfactory nerve (I) is entirely sensory and conveys impulses related to smell. 2. The optic nerve (II) is also entirely sensory and conveys impulses related to sight. 3. The oculomotor nerve (III) is a motor nerve. It controls movements of the eyeball and upper eyelid and conveys impulses related to muscle sense or position called proprioception. Its parasympathetic function causes constriction of the pupil of the eye. 4. The trochlear nerve (IV) is a motor nerve. It controls movement of the eyeball and conveys impulses related to muscle sense. It is the smallest of the cranial nerves. 5. The trigeminal nerve (V) is a mixed nerve and it is the largest of the cranial nerves. It has three branches: the maxillary, the mandibular and the ophthalmic. It controls chewing movements and delivers impulses related to touch, pain and temperature in the teeth and facial area. 6. The abducens nerve (VI) is a motor nerve that controls movement of the eyeball. 7. The facial nerve (VII) is a mixed nerve. It controls the muscles of facial expression and conveys sensations related to taste. Its parasympathetic function controls the tear and salivary glands. 8. The vestibulocochlear nerve (VIII) (ves-tib-yoo-loh-KOK-lee-ar NERV) is entirely sensory. It transmits impulses related to equilibrium and hearing. 9. The glossopharyngeal nerve (IX) (GLOSS-oh-fair-in-GEE-al NERV) is a mixed nerve. It controls swallowing and senses taste. Its parasympathetic function controls salivary glands. 10. The vagus nerve (X) is a mixed nerve. It controls skeletal muscle movements in the pharynx, larynx and palate. It conveys impulses for sensations in the larynx, viscera and ear. Its parasympathetic function controls viscera in the thorax and abdomen. 11. The accessory nerve (XI) is a motor nerve. It originates from the brainstem and the spinal cord. It helps control swallowing and movements of the head. 12. Finally, the hypoglossal nerve (XII) is a motor nerve. It controls the muscles involved in speech and swallowing and its sensory fibers conduct impulses for muscle sense.
There are 12 pairs of cranial nerves.
The five special senses are smell, taste, vision, hearing and balance. The senses of smell and taste are initiated by the interactions of chemicals with sensory receptors on the tongue and in the nose. Vision occurs due to the interaction of light with sensory receptors in the eye. Hearing and balance function due to the interaction of mechanical stimuli (sound waves for hearing and motion for balance) with sensory receptors in the ear.
The sense of smell is also known as the olfactory (ol-FAK-toh-ree) sense. Molecules in the air enter the nasal cavity and become dissolved in the mucous epithelial lining of the superior nasal conchae, the uppermost shelf area in the nose. Here they come in contact with olfactory neurons modified to respond to odors. These neurons are bipolar neurons. Their dendrites are found in the epithelial surface of the uppermost shelf and contact the olfactory receptor sites in the nose. The odor molecules bind to these receptor sites. The olfactory neurons transmit the impulse along their axons whose ends become enlarged olfactory bulbs. From here, they connect with association neurons to the area of the brain called the olfactory cortex found in the temporal and frontal lobes of the cerebrum. | | | |

The receptor cells are neurons that have cilia at the distal ends of their dendrites. It is these cilia that function as chemoreceptors to detect odors. These molecules first become dissolved in the mucous membrane that lines the olfactory shelf in the nose and then are detected. |
The sense of smell is closely related to the sense of taste. We use these two senses to decide whether or not to eat a particular food. Our sense of smell is complex because a small number of receptors detect a great variety of odors. It is the brain that then interprets these receptor combinations into a type of olfactory code. The exact mechanism of how this works is still being investigated by biologists. However, we do know that olfactory receptors rapidly adapt to odors and after a short time we no longer perceive the odor as intensely as it was initially detected.
Taste buds are the sensory structures found on certain papillae (pah-PILL-ay), which are elevations of the tongue that detect taste stimuli. Taste buds are also found on the palate of the roof of the mouth, in certain regions of the pharynx and on the lips of children. Each taste bud is composed of two types of cells.
The first type is specialized epithelial cells that form the exterior capsule of the taste bud. The second type of cell forms the interior of the taste bud. These cells are called taste cells and function as the receptor sites for taste. The taste bud is spherical with an opening called the taste pore. Taste hairs are tiny projections of the taste cells that extend out of the taste pore. It is these taste hairs that actually function as the receptors of the taste cell. Cranial nerves VIII, IX and X conduct the taste sensations to the brain, which perceives and interprets the taste.
Before a chemical can be tasted, it must first be dissolved in a fluid (just like the odors in the nose). The saliva produced by the salivary glands provides this fluid medium. Nerve fibers surrounding the taste cells transmit the impulses to the brain for interpretation. The sensory impulses travel on the facial (VIII), glossopharyngeal (IX) and vagus (X) cranial nerves to the gustatory (taste) cortex of the parietal lobe of the cerebrum for interpretation.
The four types of taste sensations are sweet, sour, salty and bitter. Although all taste buds can detect all four sensations, taste buds at the back of the tongue react strongly to bitter, taste buds at the tip of the tongue react strongly to sweet and salty, and taste buds on the side of the tongue respond more strongly to sour tastes. Taste sensations are also influenced by olfactory sensations. Holding one’s nose while swallowing reduces the taste sensation. This is a common practice when taking bad-tasting medicine.
The eyes are our organs of sight. They are protected by the orbits of the skull. See Chapter 7 to review the bones that make up the orbits. In addition, the eyebrows help shade the eye and keep perspiration from getting into the eye and causing an irritation to the eye. Eyelids and eyelashes protect the eye from foreign objects. Blinking of the eyelids lubricates the surface of the eye by spreading tears that are produced by the lacrimal gland. The tears not only lubricate the eye but also help to combat bacterial infections through the enzyme lysozyme, salt and gamma globulin.
The eye is a sphere filled with two fluids. The skeletal muscles that move the eye are discussed in Chapter 9. They are the rectus muscles and the oblique muscles.
The wall of the eye is composed of three layers, or tunics of tissue. The outermost layer is the sclera (SKLAIR-ah). It is white and composed of tough connective tissue. We see it as the white of the eye when looking in a mirror. The cornea (COR-nee-ah) is the transparent part of this outermost layer that permits light to enter the eye. The second layer is the choroid (KOR-oyd). It contains numerous blood vessels and pigment cells. It is black in color and absorbs light so that it does not reflect in the eye and impair vision. The innermost layer of the eye is the retina (RET-ih-nah). It is gray in color and contains the light-sensitive cells known as the rods and cones.
The ciliary (SIL-ee-air-ee) body consists of smooth muscles that hold the biconvex, transparent and flexible lens in place. The iris is the colored part of the eye consisting of smooth muscle that surrounds the pupil. The iris regulates the amount of light that enters through the diameter of the pupil. When we go into a dark room, the iris opens to allow more light to enter. When we go out into strong sunlight, the iris constricts, letting less light enter the pupil.
The interior of the eye is divided into two compartments. In front of the lens is the anterior compartment that is filled with a fluid called the aqueous humor. This fluid helps to bend light, is a source of nutrients for the inner surface of the eye and maintains ocular pressure. It is produced by the ciliary body. The posterior compartment of the eye is filled with vitreous (VIT-ree-us) humor. It too helps to maintain ocular pressure, refracts or bends light and holds the retina and lens in place.
The retina is the innermost layer of the eye and contains the photosensitive cells. The retina has a pigmented epithelial layer that helps keep light from being reflected back into the eye. The sensory layer is made up of the rods and cones. There are more rods than cones in this layer. Rods are quite sensitive to light and function in dim light but do not produce color vision. It is the cones that produce color and they require lots of light. Three different types of cones are sensitive to red, green or blue. Combinations of these cones produce all the other colors we see.

The rod and cone cells synapse with the bipolar cells of the retina. The bipolar cells synapse with ganglia cells whose axons form the optic nerve. Eventually, the fibers of the optic nerve reach the thalamus of the brain and synapse at its posterior portion and enter as optic radiations to the visual cortex of the occipital lobe of the cerebrum for interpretation.
The yellowish spot in the center of the retina is called the macula lutea. In its center is a depression called the fovea centralis. This region produces the sharpest vision, like when we look directly at an object. Medial to the fovea centralis is the optic disk. It is here that nerve fibers leave the eye as the optic nerve. Because the optic disk has no receptor cells, it is called the blind spot.
Both rods and cones contain light-sensitive pigments. Rod cells contain the pigment called rhodopsin (roh-DOP-sin). Cone cells contain a slightly different pigment. When exposed to light the rhodopsin breaks down into a protein called opsin and a pigment called retinal. Manufacture of retinal requires vitamin A. Someone with a vitamin A deficiency may experience night blindness, which is difficulty seeing in dim light.
Sight is one of our most important senses. Humans depend on sight as their main sense to survive and interact with our environment. We educate ourselves via visual input through reading, color interpretations and movement. People who lose their sight tend to develop acuity with the other senses like smell and sounds, senses that our dog and cat companions have developed to a high degree.
The external, inner and middle ear contain the organs of balance and hearing. The external ear is that part of the ear that extends from the outside of the head to the eardrum. Medial to the eardrum is the air-filled chamber called the middle ear, which contains the auditory ossicles: the malleus, incus and stapes. The external and middle ear are involved in hearing. The inner ear is a group of fluid-filled chambers that are involved in both balance and hearing.
The external ear consists of the flexible, visible part of our ear called the auricle (AW-rih-kl) composed mainly of elastic cartilage. This connects with our ear canal known as the external auditory meatus (eks-TER-nal AW-dih-tor-ee mee-ATE-us). The auricle allows sound waves to enter the ear canal, which then directs those waves to the delicate eardrum or tympanic (tim-PAN-ik) membrane. The ear canal is lined with hairs and modified sebaceous glands called ceruminous (seh-ROO-men-us) glands that produce earwax or cerumen. The hairs and earwax protect the eardrum from foreign objects. The thin tympanic membrane, which is silvery gray in color, is very delicate and sound waves cause it to vibrate.
The middle ear is the air-filled cavity that contains the three auditory ossicles or ear bones: the malleus or hammer, the incus or anvil, and the stapes or stirrup. These bones transmit the sound vibrations from the eardrum to the oval window. The two openings on the medial side of the middle ear are the oval window and the round window. They connect the middle ear to the inner ear. As the vibrations of the sound waves are transmitted from the malleus to the stapes, they are amplified in the middle ear.
In the middle ear we also find the auditory or Eustachian (yoo-STAY-shun) tube. This tube opens into the pharynx and permits air pressure to be equalized between the middle ear and the outside air, thus ensuring that hearing is not distorted. When flying in an airplane, changing altitude changes pressure; resulting in muffled sounds and pain in the delicate eardrum. We can allow air to enter or exit the middle ear through the auditory tube and thus equalize the pressure by yawning, chewing or swallowing. Sometimes we hold our nose and mouths shut and gently force air out of our lungs through the auditory tube and pop our eardrum to equalize the pressure.
The inner ear is made of interconnecting chambers and tunnels within the temporal bone. This area contains the cochlea, which is involved in hearing, and the vestibule and the semicircular canals, which are involved in balance. Balance is also called equilibrium. Static equilibrium is controlled by the vestibule and determines the position of the head in relation to gravity; kinetic equilibrium is controlled by the semicircular canals and determines the change in regard to head rotational movements.
Integumentary System 1. Temperature receptors in the skin detect changes in the external environment and transmit this information to the nervous system for interpretation about hot and cold sensations. 2. Pressure receptors in the skin detect changes in the external environment and transmit this information to the nervous system for interpretation about pleasure and pain sensations.

Skeletal System 1. The skull bones and vertebrae protect the brain and spinal cord. 2. Bones store calcium for release into the blood. Calcium is necessary for nervous transmission.

Muscular System 1. Muscular contraction depends on nerve stimulation. 2. Muscle sense and position of body parts are controlled by sensory neurons and interpretations by the nervous system.

Endocrine System
The hypothalamus of the brain, through neurosecretions, controls the actions of the pituitary gland, the master gland of the endocrine system, which controls the secretions of many hormones of other endocrine glands.
Cardiovascular System 1. Nerve impulses control heartbeat and blood pressure. 2. Nerve impulse control dilation and constriction of blood vessels, thus controlling blood flow.

Lymphatic System 1. Nervous anxiety and stress can impair the immune response, a major function of the lymphatic system. 2. The hypothalamus controls mind over body phenomena and boosts the immune response, thus fighting disease.

Digestive System 1. The autonomic nervous system controls peristalsis, resulting in mixing of food with digestive enzymes and moving food along the digestive tract. 2. Nerve impulses inform us when to empty the tract of indigestible waste.

Respiratory System 1. Respiratory rates are controlled by the nervous system, thus controlling oxygen and carbon dioxide levels in the blood. 2. The phrenic nerve controls the action of the diaphragm muscle, which controls breathing rates.

Urinary System 1. Nerve impulses to the kidneys control the composition and concentration of urine. 2. Stretch receptors in the bladder inform us when to eliminate urine from the body.

Reproductive System 1. Sperm and egg production is stimulated by the nervous system at the beginning of puberty and throughout life in men and up to menopause in women. 2. Sexual pleasure is determined by sensory receptors in various parts of the body. 3. Smooth muscle contractions stimulated by the nervous system initiate childbirth and delivery. 4. Sucking at the breast by the newborn stimulates milk production in the mammary glands.
The sense of smell is the olfactory sense.
In the cilia that detect odors are chemoreceptors.
The taste hairs actually function as the receptors of the taste cells.
The tongue detects four taste types: sweet and salty at the tip, sour at the sides and bitter at the back.
The two openings on the medial side of the middle ear are oval window and the round window.
The vestibule and the semicircular canals are involved in balance.
The white, outermost layer of the eyeball composed of tough connective tissue is the sclera.
The area of sharpest vision in the retina is known as the fovea centralis.
The innermost layer of the eye is called the retina.
The area of the retina where the nerve fibers leave the eye is known as the optic disk.
The thin, delicate, silvery-gray membrane that separates the external ear canal from the middle ear is known as the tympanic membrane or eardrum.
Jamari has had a stuffy nose. Now, his throat is sore and everything sounds muffled. How did the microorganisms travel from his nose to his ears? Through the auditory tube that leads from the middle ear to the pharynx
CHAPTER 12
The endocrine system exerts chemical control over the human body by maintaining the body’s internal environment within certain narrow ranges. See Concept Maps for the Endocrine System (Both Structure and Function). This is known as homeostasis (hom-ee-oh-STAY-sis). This maintenance of homeostasis, which involves growth, maturation, reproduction, metabolism and human behavior, is shared by both the endocrine system and the nervous system in a unique partnership.
It is the hypothalamus of the brain (a part of the nervous system) that sends directions via chemical signals (neurotransmitters) to the pituitary gland (a part of the endocrine system). The pituitary is occasionally referred to as the master gland of the system because many of its hormones (chemical signals) stimulate the other endocrine glands to secrete their hormones.
The endocrine glands are ductless glands that secrete their hormones directly into the bloodstream. The blood circulatory system then carries these chemical signals to target organs where their effects are seen as specific responses. These chemical signals or hormones help regulate metabolism, water and electrolyte concentrations in cells, growth, development and the reproductive cycles. Endocrine glands are ductless, as opposed to exocrine glands, which have ducts by which their secretions are transported directly to an organ or the body surface, such as sweat glands to the surface of the body and salivary glands to the mouth.
Endocrine glands are ductless glands which mean they secrete their hormones directly into the bloodstream.
Anabolic steroids are variants of testosterone.
Athletes use anabolic steroids to build muscle mass
Homeostasis is the maintenance of the body within certain narrow limits, via the chemical control of the endocrine system.
Glands that secrete their hormones directly into the bloodstream, which carries them to target organs, are known as: endocrine glands
Hormones control the internal environment of the body from the cellular level to the organ level of organization. They control cellular respiration, cellular growth and cellular reproduction. They control the fluids in the body, such as water amounts and balances of electrolytes. They control the secretion of other hormones. They control our behavior patterns. They play a vital role in the reproductive cycles of men and women. In addition, they regulate our growth and development cycles.
This chemical control of the body functions primarily as a negative feedback system. In our homes, our furnaces and thermostats operate as a negative feedback system. We set our thermostat to a particular temperature and when the temperature of our home falls below that set temperature, the thermostat causes the furnace to turn on. Once the temperature inside reaches the set temperature on the thermostat, it sends another signal to the furnace to shut off.
Hormonal systems function in the same way. When the concentration of a particular hormone reaches a certain level in the body, the endocrine gland that secreted that hormone is inhibited, (the negative feedback) and the secretion of that hormone ceases or decreases significantly. Later as the concentration of that gland’s hormone falls below normal levels, the inhibition of the gland ceases and it begins to produce and secrete the hormone once again. This kind of a negative feedback system helps to control the concentrations of a number of hormones in our bodies.
Hormones can be classified into three general chemical categories. 1. The simplest group includes hormones that are modified amino acids. Examples are the hormones secreted by the adrenal medulla, epinephrine and norepinephrine, and the hormones secreted by the posterior pituitary gland, oxytocin and vasopressin. 2. The second category is the protein hormones: insulin from the pancreatic islets and the gonad-stimulating hormones and growth hormone from the anterior pituitary gland. 3. The third category of hormones is the steroid hormones, which are lipids. Examples are cortisol from the adrenal cortex and estrogen and testosterone produced by the gonads.
The modified amino acid and protein hormones bind to membrane-bound receptor sites on the cells of target organs. The steroid hormones diffuse across the cell membrane and bind to intracellular (inside the cell) receptor molecules. The steroid hormones are soluble in lipids and can diffuse across the lining of the stomach and intestine and get to the circulatory system. They can be taken orally to treat illnesses. Birth control pills made of synthetic estrogen and progesterone hormones and steroids that combat inflammation are taken orally.
However, the protein and modified amino acid hormones, like insulin, must be injected because they cannot diffuse across the intestinal lining because they are not soluble in lipids. They are broken down before they are transported across the lining of the digestive tract and thus their effect is destroyed. Therefore, insulin must be injected to treat diabetes mellitus. The other form of diabetes is diabetes insipidus, which is caused by a deficiency in the antidiuretic hormone (ADH).
Negative feedback means that when a hormone reaches a certain level, the gland’s secretion is inhibited.
Hormones can be classified into 3 categories.
The simplest group of hormones is the modified amino acids.
The second category of hormones is the protein hormones steroids are the third kind of hormones.
Steroid hormones are soluble in lipids.
Because they cannot diffuse across the intestinal lining, protein and modified amino acid hormones, like insulin, must be injected.
Daniel and Kyle are playing sand volleyball on a hot summer day. During a break, Daniel grabs a soda to drink. Kyle chooses water because he knows that caffeine is a diuretic. What effect will that caffeine have on ADH secretion? ADH secretion will increase, trying to counterbalance the loss of fluid.
Out on a camping trip, Ryan comes face to face with a large grizzly bear. His heart rate and respiratory rate soar. What endocrine gland is releasing which hormone(s) in response to the bear? The adrenal medulla is releasing epinephrine and norepinephrine.
The hypothalamus (high-poh-THAL-ah-mus) of the brain is the inferior part of the diencephalon. It has a unique role with the endocrine system because it plays a major role in controlling secretions from the pituitary gland. There is a funnel-shaped stalk, called the infundibulum (in-fun-DIB-yoo-lum) that extends from the floor of the hypothalamus connecting it to the pituitary gland.
Historically, the pituitary gland is referred to as the master gland of the endocrine system because it controls the secretions of many other endocrine glands. However, in actuality, it is the hypothalamus of the brain that sends neural and chemical signals to the pituitary gland; hence, the hypothalamus controls the pituitary gland. This relationship is akin to a concert performance. The conductor, like the pituitary gland, tells the various sections of the orchestra (the other endocrine glands) when and how to play the music. However, the conductor gets information from the sheet music or score (like the role of the hypothalamus).
Nerve cells in the hypothalamus produce chemical signals called releasing hormones and releasing inhibitory hormones. These hormones, which are actually neurosecretions, either stimulate or inhibit the release of a particular hormone from the pituitary gland. These releasing hormones enter a capillary bed in the hypothalamus and are transported through a portal vein in the infundibulum to a second capillary bed of the anterior pituitary gland. After leaving the capillaries, they bind to receptors controlling the regulation of hormone secretion from the pituitary gland.
It is within the hypothalamus of the brain and the pituitary gland that the interactions and relationships between the endocrine and nervous systems are controlled and maintained. Conversely, due to negative feedback, the hormones of the endocrine system can influence the functions of the hypothalamus.
The hypothalamus sends directions to the pituitary gland by chemical signals
The chemical signals of the hypothalamus are called releasing hormones and releasing-inhibitory hormones
The pituitary (pih-TYOO-ih-tayr-ee) gland is also called the hypophysis (high-POFF-ih-sis). A small gland about the size of a pea, some of its hormones affect the functions of many other endocrine glands such as the testes, ovaries, the adrenal cortex and the thyroid gland. It is situated in a depression of the sphenoid bone below the hypothalamus of the brain. It is divided into two lobes, a larger anterior pituitary lobe and a smaller posterior pituitary lobe.
The anterior pituitary lobe produces seven hormones: 1. Growth Hormone (GH) 2. Thyroid-Stimulating Hormone (TSH) 3. Adrenocorticotropic Hormone (ACTH) 4. Melanocyte-Stimulating Hormone (MSH) 5. Follicle-Stimulating Hormone (FSH) 6. Luteinizing Hormone (LH) 7. Lactogenic Hormone (LTH)
Growth hormone (GH) stimulates cell metabolism in most tissues of the body, causing cells to divide and increase in size. It increases protein synthesis and the breakdown of fats and carbohydrates. It stimulates the growth of bones and muscles.
If a young person suffers from too little GH as a result of abnormal development of the pituitary gland, a condition called pituitary dwarfism results. The person remains small, although body proportions are normal. The most famous pituitary dwarf was Charles Stratton, known as Tom Thumb, who was employed by P. T. Barnum in his circus. He died in 1888 at the age of 45 and was less than 1 meter tall.
On the other hand, too much GH during childhood results in gigantism. Excess secretion of GH after childhood when bone has stopped growing results in acromegaly. Bones widen especially in the face, hands and feet. However, in the majority of children, the anterior pituitary produces just the right amount of GH, resulting in normal growth rates. Checkups with the family doctor during childhood help to monitor the rate of growth and development. In the United States, it is now rare to see a pituitary dwarf or giant.
Secretion of GH is controlled by two releasing hormones from the hypothalamus: one stimulates secretion and the other inhibits it. Peak secretions of GH occur during periods of sleep, exercise and fasting. Growth is also influenced by nutrition, genetics and the sex hormones during puberty.
Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to produce its hormone. The rate of TSH secretion is regulated by the hypothalamus, which produces thyrotropin-releasing hormone (TRH), which stimulates the anterior pituitary lobe to secrete TSH.
Adrenocorticotropic (ad-ree-noh-KOR-tih-koh-TROH-pik) hormone (ACTH) stimulates the adrenal cortex to secrete its hormone called cortisol. ACTH secretion is regulated by corticotropin-releasing hormone (CRH) produced by the hypothalamus. ACTH is involved with the glucose-sparing effect and helps reduce inflammation as well as stimulating the adrenal cortex.
Melanocyte-stimulating hormone (MSH) increases the production of melanin in melanocytes in the skin, thus causing a deepening pigmentation or darkening of the skin.
Follicle-stimulating hormone (FSH) stimulates development of the follicles in the ovaries of females. In males, it stimulates the production of sperm cells in the seminiferous tubules of the testes.
Luteinizing (LOO-tee-in-eye-zing) hormone (LH) stimulates ovulation in the female ovary and production of the female sex hormone progesterone. It helps maintain pregnancy. In males, it stimulates the synthesis of testosterone in the testes to maintain sperm cell production.
Lactogenic hormone (LTH), also known as prolactin (proh-LACK-tin), stimulates milk production in the mammary glands following delivery in a pregnant female. It also maintains progesterone levels following ovulation and during pregnancy in women. In males, it appears to increase sensitivity to LH and may cause a decrease in male sex hormones
The posterior pituitary lobe consists primarily of nerve fibers and neuroglial cells that support the nerve fibers, whereas the anterior lobe is primarily glandular epithelial cells. Special neurons in the hypothalamus produce the hormones of the posterior pituitary lobe. These hormones pass down axons through the pituitary stalk to the posterior lobe, and secretory granules near the ends of the axons store the hormones. These hormones include: 1. Antidiuretic Hormone 2. Oxytocin
Antidiuretic (an-tye-dye-yoo-RET-ik) hormone (ADH), also known as vasopressin (vaz-oh-PRES-sin), maintains the body’s water balance by promoting increased water reabsorption in the tubules of the nephrons of kidneys, resulting in less water in the urine. If secreted in large amounts, ADH can cause constriction of blood vessels, hence its other name vasopressin. A deficiency of ADH can result in a condition known as diabetes insipidus.
A deficiency of ADH can result in a condition known as diabetes insipidus. Individuals with this condition produce 20 to 30 liters of urine daily. They can become severely dehydrated. They lose essential electrolytes, resulting in abnormal nerve and cardiac muscle functions. This condition can be treated by taking ADH as injections or in the form of a nasal spray. Again the hypothalamus regulates ADH secretion through osmoreceptors that detect changes in the osmotic pressure of body fluids.
Dehydration, caused by lack of sufficient water intake, increases blood solute concentrations and these osmoreceptors signal the posterior lobe to release ADH. This causes the kidneys to conserve water. Conversely, taking in too much water or drinking too much fluid dilutes blood solutes, inhibiting ADH secretion so the kidneys excrete a more dilute (more water in it) urine until the concentration of solutes in body fluids returns to normal. In contrast, a diuretic increases urine secretion.
Oxytocin (ok-see-TOH-sin) (OT) stimulates contraction of smooth muscles in the wall of the uterus. Stretching of uterine and vaginal tissues late in pregnancy stimulates production of OT so that uterine contractions develop in the late stages of childbirth. OT also causes contraction of cells in the mammary glands causing milk ejection or lactation, forcing the milk from the glandular ducts into the nipple during breastfeeding of the newborn infant.
Occasionally, commercial preparations of OT are administered to induce labor if the uterus does not contract sufficiently on its own during childbirth. It is also given to women after childbirth to constrict blood vessels of the uterus to minimize the risk of hemorrhage.
The pituitary gland is also called the hypophysis
The pituitary gland has two lobes, the larger anterior lobe and the smaller posterior lobe.
The larger of the lobes produces 7 hormones
TSH stimulates the thyroid gland to produce its hormone.
MSH increases the production of melanin and this darkens the skin.
Luteinizing hormone stimulates ovulation in the female.
ADH inhibits the body from excreting water in the urine.
Oxytocin stimulates contraction of the uterus and also stimulates lactation. follicle-stimulating hormone stimulates development of the follicles in the ovaries of females. gigantism occurs as a result of excessive secretion of the growth hormone before the bones stop growing.
Excessive secretion of the growth hormone after childhood characterized by an enlarged face, hands, and feet is known as: acromegaly
The hormone that maintains the body's water balance by promoting increased water reabsorption by the kidneys is the antidiuretic hormone known as vasopressin
If a young person suffers from too little growth hormone as a result of abnormal development of the pituitary gland, the resulting condition is dwarfism
A condition of the pituitary gland due to a deficiency of ADH in which the individual produces 20 to 30 liters of urine daily and can become severely dehydrated is known as diabetes insipidus
The thyroid gland consists of two lobes connected by a smaller band called the isthmus. The lobes are situated on the right and left sides of the trachea and thyroid cartilage just below the larynx. It is a highly vascular, large endocrine gland covered with a capsule of connective tissue. It is made up of spheres of cells called follicles. These follicles are composed of simple cuboidal epithelium, which produce and secrete the thyroid hormones. Thyroid output is regulated by the hypothalamus, which signals the pituitary to release TSH to increase thyroid production.

The thyroid gland requires iodine to function properly. In the United States iodized salt is used as a way to ensure the intake of adequate amounts of iodine in the diet. In countries without adequate amounts of iodine in the diet, the thyroid gland enlarges forming a goiter (GOY-ter). However, proper amounts of iodine cause the thyroid gland to effectively produce its hormones. One hormone is thyroxine (thigh-ROXS-in), also known as tetraiodothyronine (teh-trah-eye-oh-doh-THIGH-roh-neen), which contains four iodine atoms and is abbreviated as T4. The other hormone is triiodothyronine (try-eye-oh-doh-THIGH-roh-neen), which contains three iodine atoms and is abbreviated as T3.
These hormones regulate the metabolism of carbohydrates, fats and proteins. These hormones are necessary for normal growth and development as well as for nervous system maturation. They cause an increase in the rate of carbohydrate and lipid breakdown into energy molecules as well as increasing the rate of protein synthesis.
A lack of or low level of thyroid hormones is called hypothyroidism (high-poh-THIGH-royd-izm). In young children, this can result in a condition known as cretinism (KREE-tin-izm). The child with this condition is mentally retarded and does not grow to normal stature. In adults, this condition results in a lowered rate of metabolism, causing sluggishness, being too tired to perform normal daily tasks and an accumulation of fluid in subcutaneous tissues called myxedema (miks-eh-DEE-mah).
Too much secretion of thyroid hormones causes hyperthyroidism (high-per-THIGH-royd-izm). This results in extreme nervousness, fatigue and an elevated rate of body metabolism. Graves’ disease is a type of hyperthyroidism caused by overproduction of thyroid hormone. It is often associated with an enlarged thyroid gland or goiter and bulging of the eyeballs known as exophthalmia (eks-off-THAL-mee-ah).
Besides secreting these two thyroid hormones, the extrafollicular cells of the thyroid gland secrete a hormone called calcitonin (kal-sih-TOH-nin). This hormone lowers the calcium and phosphate ion concentration of the blood by inhibiting the release of calcium and phosphate ions from the bones and by increasing the excretion of these ions by the kidneys.
Thyroid hormone secretion is controlled by TSH produced by the anterior pituitary gland. Increased levels of thyroid hormones, through the negative feedback mechanism, inhibit the anterior pituitary gland from releasing more TSH and the hypothalamus from secreting TSH-releasing hormone. Because of negative feedback, the thyroid hormones fluctuate daily within a narrow range of concentration in the blood.
The parathyroid glands are four glands about the size of raisins that are embedded in the posterior surface of the thyroid gland. There are two in each lobe of the thyroid, a superior and an inferior gland. Each gland consists of many tightly packed secreting cells called chief cells and oxyphil cells close to capillary networks.

The parathyroid glands secrete a single hormone called parathyroid hormone or parathormone (PTH). PTH inhibits the activity of osteoblasts and causes osteoclasts to break down bone matrix tissue, thus releasing calcium and phosphate ions into the blood. In addition, PTH causes the kidneys to conserve blood calcium and stimulates intestinal cells to absorb calcium from digested food in the intestine. This hormone raises blood calcium to normal levels.
Vitamin D also increases absorption of calcium by the intestines. Ultraviolet light from the sun acting on the skin is necessary for the first stage of vitamin D synthesis. The final stage of synthesis occurs in the kidneys and is stimulated by PTH. Vitamin D can also be supplied in the diet.
An abnormally high level of PTH secretion is known as hyperparathyroidism and can be caused by a tumor in a parathyroid gland. This condition results in the breakdown of bone matrix, and bones become soft and deformed and can easily fracture. Elevated calcium levels in the blood cause muscles and nerves to become less excitable, resulting in muscle weakness and fatigue. Excess calcium and phosphate ions may become deposited in abnormal places resulting in kidney stones.
An abnormally low level of PTH is called hypoparathyroidism. This can be caused by surgical removal of the thyroid and parathyroid glands or by injury to the glands. The decreased level of PTH reduces osteoclast activity, reduces rates of bone matrix breakdown or resorption and reduces vitamin D formation. Bones will remain strong but the blood calcium level decreases result in nerves and muscles becoming abnormally excitable, producing spontaneous action potentials. This can cause frequent muscle cramps or tetanic contractions. If respiratory muscles are affected, breathing failure and death can occur.
A goiter is an enlarged thyroid gland.
The parathyroid glands consist of chief cells and oxyphil cells.
The hormone from the parathyroid glands functions to balance calcium levels in the body.
Grave’s disease is a type of hyperthyroidism caused by overproduction of thyroid hormone, often associated with an enlarged thyroid gland or goiter and bulging eyeballs.
Bulging of the eyeballs due to hyperthyroidism is known as exophthalmia
A condition due to hypothyroidism in young children in which the child is mentally retarded and does not grow to normal stature is known as cretinism
The hormone that lowers the calcium and phosphate ion concentration of the blood by inhibiting the release of calcium phosphate ions from the bones and increasing the excretion of these ions by the kidneys is calcitonin
Julie, a 41-year-old mother of three has been extremely lethargic lately. She thinks it must be due simply to her hectic schedule and lack of sleep. But she also notices she’s gaining weight and losing hair, and her skin has become dry and rough. Could this be a problem with an endocrine gland? Which one(s)?
Thyroid gland—she is suffering from hypothyroidism.
The adrenal (ad-REE-nal) glands are also known as the suprarenal (soo-prah-REE-nal) glands. They are small glands found on top of each kidney. The inner part of each gland is called the adrenal medulla and the outermost part is called the adrenal cortex. Each section functions as a separate endocrine gland.

The adrenal medulla produces large amounts of the hormone adrenalin (ad-REN-ih-lin), also known as epinephrine (ep-ih-NEF-rin), and small amounts of norepinephrine (nor-ep-ih-NEF-rin) or noradrenalin. These hormones are released in response to signals from the sympathetic division of the autonomic nervous system. Epinephrine and norepinephrine are commonly referred to as the fight or flight hormones because they get the body prepared for stressful situations that require vigorous physical activity. When a person senses danger and experiences stress, the hypothalamus of the brain triggers the adrenal gland via the sympathetic division of the autonomic nervous system to secrete its hormones.
These hormones cause the breakdown of glycogen in the liver to glucose and the release of fatty acids from stored fat cells. The glucose and fatty acids are released into the bloodstream as a quick source for synthesis of adenosine triphosphate (ATP) and increased metabolic rates. Heartbeat and blood pressure rates increase to get the glucose and fatty acids to muscle cells. Blood flow decreases to internal organs and skin but increases to muscle cells. The lungs take in more oxygen and get rid of more carbon dioxide. These changes all prepare our body to either fight or flee the stressful situation.
The adrenal cortex makes up the bulk of the adrenal gland. Its cells are organized into three densely packed layers of epithelial cells, forming an inner, middle and an outer region of the cortex. The outer layer of the adrenal cortex secretes a group of hormones called mineralocorticoid hormones because they regulate the concentration of mineral electrolytes. The most important of these hormones is aldosterone (al-DOS-ter-ohn), which regulates sodium reabsorption and potassium excretion by the kidneys.
The middle layer of the adrenal cortex secretes cortisol (KOR-tih-sahl), also known as hydrocortisone (HIGH-droh-KOR-tih-zone), which is a glucocorticoid hormone. Cortisol stimulates the liver to synthesize glucose from circulating amino acids. It causes adipose tissue to break down fat into fatty acids and causes the breakdown of protein into amino acids. These molecules are released into circulating blood to be taken up by tissues as a quick source of energy. The action of cortisol helps the body during stressful situations and helps maintain the proper glucose concentration in the blood between meals.
Cortisol also helps reduce the inflammatory response. Cortisone (KOR-tih-zone), a steroid closely related to cortisol, is often given as a medication to reduce inflammation and as a treatment for arthritis. Dr. Percy Julian, an African American scientist, discovered how to synthetically produce cortisone and to use it as a treatment for the pain produced by the swelling in arthritic joints.
Cells in the inner zone of the adrenal cortex produce the adrenal sex hormones called the androgens (AN-droh-jenz). These are male sex hormones. Small amounts of androgens are secreted by the adrenal cortex in both men and women. In adult men, most androgens are secreted by the testes. Androgens stimulate the development of male sexual characteristics. In adult women, the adrenal androgens stimulate the female sex drive.
If the adrenal cortex fails to produce enough hormones, a condition known as Addison’s disease develops. President John F. Kennedy suffered from Addison’s disease and was under regular medical care for its treatment. Although President Kennedy always looked tanned and healthy, a bronzing of the skin was a symptom of the disease. In addition, other symptoms include decreased blood sodium, low blood glucose causing fatigue and listlessness, dehydration and low blood pressure. Without treatment it can lead to death due to severe changes in electrolyte balances in the blood
Too much secretion from the adrenal cortex can lead to Cushing’s syndrome. Blood glucose concentration remains high, lowering tissue protein. Retention of sodium causes tissue fluid increase, resulting in puffy skin. The patient exhibits obesity, a moon-shaped face, skin atrophy and menstrual problems in women. Increases in adrenal male sex hormone production results in masculinizing changes in women, such as facial hair growth and lowering of voice pitch.
The pancreas has a dual role in that it is part of the digestive system where its cells, called acini, produce digestive enzymes known as pancreatic juice, and it is part of the endocrine system where its pancreatic islets, also known as the islets of Langerhans, produce the hormones insulin and glucagon (GLOO-kah-gon). These hormones regulate blood glucose levels. The pancreas is a flattened, elongated gland divided into head, body and tail portions. Refer to its anatomy in Chapter 16. It is found behind the stomach and its pancreatic duct connects to the duodenum of the small intestine. This exocrine portion of the gland (the pancreatic duct) transports its digestive juices to the intestine.
Its endocrine portion consists of two main groups of cells closely associated with blood vessels. These groups of cells are known as the pancreatic islets or islets of Langerhans. Alpha cells secrete the hormone glucagon, and beta cells secrete the hormone insulin.
After a meal that consists primarily of carbohydrates like potatoes or rice, vegetables, salad, or cereals and breads, the blood glucose concentration becomes high due to the digestive processes. At this time, beta cells release insulin into the bloodstream. Insulin promotes the glucose in the blood to be transformed in the liver into glycogen, which is stored animal starch. In addition, glucose is moved into muscle cells and adipose tissue. Through negative feedback, when blood glucose levels fall, as between meals and during the night, the secretion of insulin decreases.
During the time glucose levels decrease, alpha cells in the pancreatic islets secrete the hormone glucagon. Glucagon stimulates the liver to convert the stored glycogen into glucose, thus raising blood glucose levels. Glucagon also causes the breakdown of amino acids and their conversion into glucose to raise blood sugar levels. The breakdown of the amino acids of proteins is used by the liver to synthesize more glucose. Fats are also broken down rapidly by other tissues to provide an alternative energy source. Again a negative feedback system regulates glucagon secretion.
Low blood sugar concentrations stimulate alpha cells to secrete glucagon. As blood sugar levels rise, glucagon secretion decreases. This mechanism helps to prevent hypoglycemia when glucose concentration gets low as during exercise and between meals.
The maintenance of blood glucose levels within a normal range is essential to body maintenance and function. A decline in blood glucose can cause nervous system malfunctions because glucose is the main source of energy for nerve cells. If the blood glucose level gets very low, the breakdown of fats releases fatty acids and ketones, causing a lowering of blood pH, a condition known as acidosis (as-ih-DOH-sis). If blood glucose levels are too high, the kidneys produce large amounts of urine containing high amounts of glucose, which can lead to dehydration.
The anatomy of the testes and the ovaries are discussed in detail in Chapter 19. The testes, in addition to producing sperm as exocrine glands, produce the male sex hormones as endocrine glands. The principal male sex hormone is testosterone (tess-TOS-ter-ohn). This hormone is responsible for the development of the male reproductive structures, and at puberty, the enlargement of the testes and penis. It also promotes the development of secondary male sexual characteristics, such as the growth of facial and chest hair, deepening of the voice, muscular development, bone growth resulting in broad shoulders and narrow hips. It promotes the development of the male sexual drive and aggressiveness.
In the ovaries of the female, two groups of hormones, estrogen (ESS-troh-jen) and progesterone (proh-JES-ter-ohn), promote the development of the female reproductive structures: the uterus, vagina and fallopian tubes. Secondary female sexual characteristics also develop such as breast enlargement, fat deposits on the hips and thighs, bone development resulting in broad hips and a higher pitched voice. The menstrual cycle is also controlled by these hormones.
Releasing hormones from the hypothalamus affect the anterior pituitary gland to produce the gonad-stimulating hormones: LH and LSH. These hormones control the secretion of hormones from the testes and ovaries. The hormones from the gonads have a negative feedback effect on the hypothalamus and the anterior pituitary gland. Thus, a constant, normal level of sex hormones is maintained in the body.
The thymus gland is a bi-lobed mass of tissue found in the mediastinum behind the sternum between the two lungs. This gland is most important early in life and is relatively large in young children. It is critical in the development of the immune system and is discussed further in Chapter 15. As we age, the gland shrinks and is replaced with fat and connective tissue. The gland secretes the hormone thymosin (thigh-MOH-sin), which causes the production of certain white blood cells called T lymphocytes. These T cells protect the body against foreign microorganisms, thus helping to fight infections.
The thymus gland has an important role in the development of immunity. Occasionally, an infant will be born without a thymus gland and the immune system will not develop properly. Such children are susceptible to infections and have greater difficulty fighting off microbial organisms.
The pineal (PIN-ee-al) gland or body is a small pinecone-shaped structure found between the two cerebral hemispheres attached to the upper part of the thalamus near the top of the third ventricle. The pineal gland produces the hormone melatonin (mel-ah-TOH-nin), which is secreted directly into cerebrospinal fluid.
Melatonin has a number of effects on the body and research continues on the hormone. It inhibits the secretion of the gonadotropin hormones LH and LSH from the anterior pituitary gland, thus inhibiting the functions of the reproductive system. Bright light inhibits the secretion of melatonin. Studies have indicated that melatonin regulates circadian rhythms. In bright light, with little melatonin, people “feel good” and their fertility increases. High levels of melatonin produced in the dark cause individuals to feel depressed and tired, bringing on sleep.
Melatonin affects our sleep-wake patterns and maintains our biological cycles. Nerve impulses originating in the retina of the eyes send light information to the pineal gland. In dark or dim light, nerve impulses from the eyes decrease and melatonin secretion increases. Melatonin also plays a role in the onset of puberty and in the female reproductive cycle.
Serotonin (sayr-oh-TOH-nin) is also secreted by the pineal gland and acts as a neurotransmitter and vasoconstrictor. It stimulates smooth muscle contraction and inhibits gastric secretions.
The adrenal medulla secretes adrenalin ; the adrenal cortex secretes a number of hormones, the most important of which is aldosterone.
The middle layer of the adrenal cortex secretes cortisol, which is also known as hydrocortisone.
The sex hormones secreted by the inner layer of the adrenal cortex are androgens.
The islets of Langerhans are located on the pancreas, and they produce the hormones insulin and glucagon.
Glycosuria is a condition of elevated sugar in the urine
The thymus gland is important in the development of immunity cortisone is a steroid closely related to cortisol that is often given as a medication to reduce inflammation and as a treatment for arthritis.
A condition of excessive thirst experienced by a diabetic person who has lost a large amount of fluid in the urine is called polydipsia.
Serotonin, secreted by the pineal gland, is a hormone that stimulates smooth muscle contraction and inhibits gastric secretions. diabetes mellitus is a common condition of the endocrine system in which the pancreas fails to produce enough insulin, resulting in chronic elevations of glucose in the blood.
A condition due to too much secretion from the adrenal cortex in which the individual experiences puffy skin, obesity, a moon-shaped face, and masculinizing changes in women is known as Cushing’s syndrome
A state of increased acidity of the blood due to the breakdown of fats when the blood sugar level is very low is known as acidosis
A condition of the adrenal cortex characterized by bronzing of the skin, decreased blood sodium, low blood glucose, low blood pressure, fatigue, listlessness, and dehydration is called Addison’s disease
The cells in the islets of Langerhans of the pancreas responsible for secreting insulin are the beta cells
The hormone secreted by the alpha cells of the pancreas responsible for stimulating the liver to convert the stored glycogen into glucose in times of extremely low blood sugar levels is glucagon
The medical term for excessive thirst, or craving large amounts of liquid, is known as polydipsia
The medical term for elevated glucose level in the blood is hyperglycemia
Integumentary System 1. Melanocyte production in the skin is caused by melanocyte-stimulating hormone from the anterior pituitary. 2. Melanocytes produce melanin, causing a darker pigmentation to skin for protection against the harmful rays of the sun. 3. Androgens activate sebaceous glands; estrogen increases hydration of skin.

Skeletal System 1. Calcium concentrations in bone are controlled by the hormones calcitonin and parathormone. 2. Nerve cells of the hypothalamus function properly due to proper calcium ion concentration. 3. Bones protect the endocrine glands in the brain, pelvis and chest.

Muscular System 1. Hormones can cause increased heartbeat rates, which help to increase the amount of blood-carrying oxygen and nutrients to exercising muscle cells. 2. Growth hormone stimulates muscular development.

Nervous System 1. Nerve cells of the hypothalamus control the secretions of the pituitary gland. 2. Through negative feedback, hormonal levels control the secretions of the hypothalamus.

Cardiovascular System 1. The blood carries hormones to their target organs. 2. Heart rates and the diameter of blood vessels are controlled by hormones.

Lymphatic System 1. Hormones stimulate the production of T lymphocytes. 2. Hormones are involved in the development of the immune system in children. 3. Lymph can be a route for hormone transport.

Digestive System 1. Glucose levels in the blood are controlled by hormones. 2. Excess glucose is stored in the liver as glycogen and is made available to cells between meals by the combined actions of insulin and glucagon. 3. Hormones also affect digestive activities, such as increased appetites during puberty caused by higher rates of metabolism.

Respiratory System 1. Low levels of oxygen in the blood stimulate hormonal production of red blood cell formation in bone marrow. 2. Red blood cells transport oxygen from the lungs to body cells and carbon dioxide waste from cells to the lungs. 3. Epinephrine increases breathing rates.

Urinary System 1. Hormones control kidney function. 2. Kidneys control body water levels and balances of the electrolytes in the blood.

Reproductive System 1. The sex hormones stimulate the development of the reproductive structures. 2. Sex hormones also stimulate the development of secondary male and female sexual characteristics. 3. Sex hormones stimulate the development of egg cells and sperm cells.
CHAPTER 13
Blood is a uniquely specialized connective tissue in that it consists of two components: the formed elements of blood, or the blood cells, and the fluid part of blood or plasma. The formed elements of blood are the red blood cells (RBCs) or erythrocytes (eh-RITH-roh-sightz), the white blood cells (WBCs) or leukocytes (LOO-koh-sightz) and the platelets or thrombocytes (THROM-boh-sightz). Plasma, a viscous fluid, accounts for about 55% of blood; the formed elements make up about 45% of the total volume of blood. An average woman has about 5 liters of blood; an average man has approximately 6 liters of blood in the body. Blood accounts for about 8% of total body weight.
Pumped by the heart and carried by blood vessels throughout the body, blood is a complex liquid that performs a number of critical functions. These functions relate to maintaining homeostasis.
Blood transports oxygen from the lungs, where it enters the RBCs, to all cells of the body. Oxygen is needed by the cells for cellular metabolism. Blood also transports carbon dioxide from the cells, where it is produced as a waste product of cellular metabolism, to the lungs to be expelled from the body.
Blood carries nutrients, ions and water from the digestive tract to all cells of the body. It also transports waste products from the body’s cells to the sweat glands and kidneys for excretion.
Blood transports hormones from endocrine glands to target organs in the body. It also transports enzymes to body cells to regulate chemical processes and chemical reactions. Blood helps regulate body pH through buffers and amino acids that it carries. The normal pH of blood is slightly basic (alkaline) at 7.35 to 7.45. Blood plays a role in the regulation of normal body temperature because it contains a large volume of water (the plasma), which is an excellent heat absorber and coolant.
Blood helps to regulate the water content of cells through its dissolved sodium ions; thus, it plays a role in the process of osmosis. It is through the clotting mechanism that blood helps prevent fluid loss when blood vessels and tissues are damaged.
Finally, blood plays a vital role in protecting the body against foreign microorganisms and toxins through its special combat-unit cells, the leukocytes.
Platelets are also called thrombocytes
Blood transports oxygen from the lungs and carbon dioxide to the lungs.
The regulation of water by the blood plays a role in the process of osmosis
Another hereditary blood disease causing suppressed hemoglobin production is thalassemia
Infectious mononucleosis is caused by the Epstein-Barr virus.
A thrombocyte, a formed blood element, is also known as a platelet
A genetically inherited clotting disorder associated with the expression of a recessive gene on the X chromosome, inherited from the mother and passed down to male children, is known as hemophilia
A type of cancer in which there is abnormal, excessive production of white blood cells is known as leukemia
An inherited condition in which erythrocytes rupture or are destroyed at a faster rate than normal is known as hemolytic anemia
A condition that results from vitamin B12 deficiency, nutritional deficiencies, or from excessive iron loss from the body, resulting in lower than normal erythrocyte production is known as iron-deficiency anemia
The medical term for blood poisoning, which is caused by an infection of microorganisms and their toxins in the blood, is septicemia
One of the most common classifications of the formed elements or cells of blood is erythrocytes or red blood cells (RBCs), which make up about 95% of the volume of blood cells.

Another of the most common classifications of the formed elements or cells of blood is leukocytes or white blood cells (WBCs) which are divided into two subcategories: the granular leukocytes and the agranular or nongranular leukocytes.

The granular leukocytes have granules in their cytoplasm when stained with Wright’s stain. There are three types: 1. neutrophils (NOO-troh-fillz), which make up 60% to 70% of WBCs 2. esoinophils (ee-oh-sin-oh-fillz), which make up 2% to 4% of WBCs 3. Basophils (BAY-soh-fillz), which make up 0.5% to 1% of WBCs.

The agranular or nongranular leukocytes do not show granules in their cytoplasm when stained with Wright’s stain. There are two types: 1. Monocytes (MON-oh-sightz), which make up about 3% to 8% of WBCs 2. Lymphocytes (LIM-foh-sightz), which make up about 20% to 25% of WBCs
Another of the most common classifications of the formed elements or cells of blood is thrombocytes or platelets.

There are 700 times more RBCs in blood than WBCs and at least 17 times more RBCs than platelets.

Plasma is the fluid component of blood; 91% of plasma is water. About 7% are the proteins albumin (al-BYOO-men), globulins (GLOB-yoo-linz) and fibrinogen (fih-BRIN-oh-jen). Albumin plays a role in maintaining osmotic pressure and water balance between blood and tissues. Some examples of globulins are antibodies and complement, which are important in the immune response of the body. Other globulins act as transport molecules for hormones and carry them to target organs. Fibrinogen plays a vital role in the clotting mechanism. The remaining 2% of plasma consist of solutes such as ions, nutrients, waste products, gases, enzymes and hormones.
Blood storage techniques were developed by Dr. Charles Drew, an African American scientist. He is best known for his research on blood plasma. His blood preservation discoveries led to the formation of blood banks in the United States and Great Britain during World War II. He was director of the first American Red Cross Blood Bank.
Blood cell formation is known as hematopoiesis (hem-ah-toh-poy-EE-sis). Hematopoiesis occurs in red bone marrow, which is also known as myeloid tissue. All blood cells are produced by red bone marrow. However, certain lymphatic tissue such as the spleen, tonsils and lymph nodes produce agranular leukocytes (lymphocytes and monocytes). They assist in the production of those blood cells. All blood cells develop from undifferentiated mesenchymal cells called stem cells or hematocytoblasts (hee-MAT-oh-SIGHT-oh-blastz).
Some stem cells will differentiate into proerythroblasts, which will eventually lose their nuclei and become mature RBCs. Some stem cells will become myeloblasts. These cells will develop into progranulocytes. Some of these cells will develop into basophilic myelocytes and will mature into basophils, others will develop into eosinophilic myelocytes and will mature into eosinophils, while still others will develop into neutrophilic myelocytes and will mature into neutrophils. Other stem cells will become lymphoblasts and will mature into lymphocytes; some stem cells will become monoblasts and will mature into monocytes. Finally, some stem cells will become megakaryoblasts and will undergo multipolar mitosis of the nucleus to mature into blood platelets. All stages of blood cell development will be found in red bone marrow tissue.
The white cells are the leukocytes and the red cells are the erythrocytes.
Neutrophils, eosinophils and basophils are the granular leukocytes.
Globulin carries hormones to target organs.
Erythrocytes, or red blood cells, make up about 95% of the volume of blood cells.
The blood protein albumin plays a role in maintaining osmotic pressure and water balance between blood and tissues.
A plasma protein that plays a vital role in the clotting mechanism is fibrinogen
What are Erthyroctyes? Erythrocytes appear as biconcave disks with edges that are thicker than the center of the cell, looking somewhat doughnut-shaped. They do not have a nucleus and are simple in structure. They are composed of a network of protein called stroma, cytoplasm, some lipid substances including cholesterol and a red pigment called hemoglobin (hee-moh-GLOH-bin). Hemoglobin constitutes 33% of the cell’s volume. Erythrocytes contain about 280 million molecules of hemoglobin per erythrocyte. Because they have lost their nuclei, they do not divide. They live for approximately 120 days. | |

The primary function of erythrocytes is to combine with oxygen in the lungs and to transport it to the various tissues of the body. It then combines with carbon dioxide in tissues and transports it to the lungs for expulsion from the body. The pigment hemoglobin allows this to happen. Hemoglobin is made of a protein called globin (GLOH-bin) and a pigment called heme (HEEM). The pigment heme contains four iron atoms. The iron atoms of heme combine with the oxygen in the lungs. In the tissues of the body, the oxygen is released and the protein globin now combines with the carbon dioxide from the interstitial fluids and carries it to the lungs where it is released.
Hemoglobin that is carrying oxygen is bright red in color, whereas hemoglobin not carrying oxygen is a darker red in color. A healthy man has 5.4 million RBCs/mm3 of blood and a healthy woman has 4.8 million RBCs/mm3 of blood. Due to menstruation and loss of blood, some women need more iron in their diet for the most efficient transport of oxygen by their blood.

Leukocytes have nuclei and no pigment. Their general function is to combat inflammation and infection. They are called white blood cells because they lack pigmentation. They are larger in size than RBCs and are carried by the blood to various tissues in the body. They have the ability to leave the blood and move into tissues by ameboid movement, sending out a cytoplasmic extension that attaches to an object while the rest of the cell’s contents then flows into that extension. In this manner, the leukocytes attack invading microorganisms and clean up cellular debris by consuming this material by phagocytosis (FAG-oh-sigh-TOH-sis), which means eating cells.
When stained with Wright’s stain, the cytoplasm of leukocytes shows the presence or absence of granules. Therefore, leukocytes are divided into the granular leukocytes and the agranular (a means without) or nongranular leukocytes. The three types of granular leukocytes are neutrophils, basophils and eosinophils. The two types of nongranular leukocytes are monocytes and lymphocytes.

Neutrophils are the most common of leukocytes. They are the most active WBCs in response to tissue destruction by bacteria. They stay in the blood for about 12 hours and then move into tissues where they phagocytize foreign substances and secrete the enzyme lysozyme (LYE-soh-zyme), which destroys certain bacteria. When pus accumulates at an infection area, it consists of cell debris, fluid and dead neutrophils.

Monocytes are also phagocytotic. They phagocytize bacteria and any dead cells or cellular debris. They are the largest leukocytes. After they leave the blood and enter tissues, they increase in size and are called macrophages (MACK-roh-fay-jeez).

Eosinophils combat irritants, such as pollen or cat hair, that cause allergies. They produce antihistamines. Their chemical secretions also attack some worm parasites in the body.

Basophils are also involved in allergic reactions. They release heparin (an anticoagulant), histamine (an inflammatory substance) and serotonin (a vasoconstrictor) into tissues.

Lymphocytes are involved in the production of antibodies and play a crucial role in the body’s immune response. They are the smallest of the leukocytes. There are several types of lymphocytes: the B lymphocytes and the T lymphocytes, which are discussed further in Chapter 15. They are involved in controlling cancer cells, destroying microorganisms and rejecting foreign tissue implants.
Leukocytes are far less numerous than RBCs, averaging from 5000 to 9000 per mm3 of blood. They can phagocytize only a certain number of substances before these materials interfere with the leukocyte’s normal metabolic activity. Therefore, their life span is quite short. In a healthy body, some WBCs will live only a few days. During infections, they may live for only a few hours.
Thrombocytes or platelets are disk-shaped cellular fragments with a nucleus. They range in size from 2 to 4 micrometers in diameter. They prevent fluid loss when blood vessels are damaged by initiating a chain of reactions that result in blood clotting. They have a life span of about a week. They are produced in red bone marrow from large megakaryocytes (meg-ah-KAIR-ee-oh-sightz).
Red blood cells do not have a(n) nucleus.
Heme contains the element iron atoms.
Although leukocytes have a nucleus, they have no pigment.
The destruction of certain bacteria is accomplished by the enzyme lysozyme.
After they leave the blood and enter tissues, monocytes increase in size.
Disk-shaped cellular fragments with a nucleus are platelets or thrombocytes.
The general function of leukocytes is to combat inflammation and infection.
Thrombocytes, or platelets, are produced in red bone marrow from large megakaryocytes.
The process by which leukocytes attack invading microorganisms and clean up cellular debris by consuming the material or eating cells is known as phagocytosis.
The white blood cells that produce antihistamines and combat irritants, such as pollen or cat hair that cause allergies, are eosinophils
The most common type of leukocytes that are the most active white blood cells in response to tissue destruction by bacteria is neutrophils
Mekelle is playing a video game where a large blob encloses smaller blobs and eats them. What white blood cell(s) are very similar to these large blobs? Monocytes macrophages
When we injure ourselves through a fall or scrape, blood vessels are damaged and blood flows into tissues and can be lost from the body. Fortunately, the body has a mechanism to stop the loss of blood and repair the damaged blood vessels and tissues. The clotting mechanism is a process that the body uses to stop the loss of blood.

When small blood vessels are damaged, smooth muscles in the vessel’s walls contract. This can stop blood loss. When larger vessels are damaged, the constriction of the smooth muscles in the vessel walls only slows down blood loss and the clotting mechanism takes over. A cut in a blood vessel causes the smooth walls of the vessel to become rough and irregular. Clotting or coagulation is a complex process that proceeds in three stages.
In the first stage, the roughened surface of the cut vessel causes the platelets or thrombocytes to aggregate, or clump together, at the site of injury. The damaged tissues release thromboplastin (throm-boh-PLAST-in). The thromboplastin causes a series of reactions that result in the production of prothrombin activator. These activities require the presence of calcium ions and certain proteins and phospholipids.
In the second stage, prothrombin (proh-THROM-bin), a plasma protein produced by the liver, is converted into thrombin. In the presence of the calcium ions, prothrombin activator converts the prothrombin into thrombin.
In the third stage, another plasma protein, soluble fibrinogen, is converted into insoluble fibrin. It is the thrombin that catalyzes the reaction that fragments fibrinogen into fibrin. Fibrin forms long threads that act like a fish net at the site of injury. The fibrin forms what we call the clot. As the clot forms, blood cells and platelets get enmeshed in the fibrin threads and the wound stops bleeding.
Clot retraction or syneresis (sih-NER-eh-sis) is the tightening of the fibrin clot in such a way that the ruptured area of the blood vessel gets smaller and smaller, thus decreasing the hemorrhage. The clear yellowish liquid that is seen after the clot forms is called serum. Serum is blood plasma without the clotting factors. Now that the hemorrhage is stopped, blood vessel tissues repair themselves by mitotic cellular division. Once the tissue is repaired, fibrinolysis (fi-brih-NOL-ih-sis) or dissolution of the blood clot occurs. This is caused by a plasma protein that digests the fibrin threads and other proteins associated with the formation of the clot.
Occasionally, unwanted clotting may occur in an undamaged blood vessel. This is brought about by the cholesterol-containing mass called plaque (PLAK) that adheres to the smooth walls of blood vessels. This results in a rough surface that is ideal for the adhesion of the platelets, thus starting the clotting mechanism. Too much cholesterol in the diet from eating too much fatty food contributes to the formation of these masses.
Clotting in such an unbroken vessel is called thrombosis (throm-BOH-sis) and the clot itself is called a thrombus (THROM-bus). A thrombus may dissolve. However, if it remains intact, it can damage tissues beneath it by cutting off oxygen supplies.
If a piece of a blood clot dislodges and gets transported by the bloodstream, it is called an embolus (IM-boh-lus). When an embolus becomes lodged in a vessel and cuts off circulation, it is called an embolism (IM-boh-lizm). When a blood clot forms in a vessel that supplies a vital organ, it is designated in a special way.
If the brain is affected, it is called a cerebral thrombosis. If the heart is affected, it is called a coronary thrombosis. If the tissues are killed, it is called an infarction (in-FARK-shun) and is often fatal. If a blood clot dislodges and travels to a vital organ like the lungs and blocks a vessel supplying that organ, it is referred to as a pulmonary embolism. To prevent embolisms from occurring after surgery, patients are expected to walk or ambulate as soon as possible so that the normal destruction of cellular and tissue debris can occur through the activities of the WBCs and phagocytosis.
In the first stage of clotting, thromboplastin is released by damaged tissues.
In the second stage of clotting, prothrombin is converted to thrombin.
The formation of the clot is a result of the production of fibrin.
After tissue repair, fibrinolysis occurs; this is a(n) dissolution of the blood clot.
Clotting in an unbroken vessel is called thrombosis.
A piece of a thrombus that breaks off is a(n) embolus.
The tightening of a fibrin clot in such a way that the ruptured area of the blood vessel gets smaller and smaller, thus decreasing hemorrhage is known as syneresis
An abnormal condition in which a blood clot becomes lodged in a blood vessel, obstructing the flow of blood in the vessel, is known as a(n) embolism
The clear yellowish liquid that is seen after a clot forms is called serum
Cedric cut his finger rather deeply. He immediately placed sterile gauze over the wound and applied pressure. What process is occurring in the wound? How will the gauze (a rough surface) accelerate this process?
The clotting process is occurring in the wound. The first step in this process is the accumulation of platelets. The rough edges of the gauze pad will make it easier to trap platelets and help a clot form faster.

Human blood is of different types and only certain combinations of these blood types are compatible. Procedures have been developed for typing blood. This ensures that donor and recipient blood transfusions are compatible. If blood groups are mismatched, agglutination (ah-gloo-tih-NAY-shun) or clumping of RBCs will occur. This is called a transfusion reaction and is caused by a reaction between protein antibodies in the blood plasma and RBC surface molecules called antigens. It is just a few of the many RBC antigens that can cause a serious transfusion reaction. These are the antigens of the ABO group and the Rh group.
Agglutination of RBCs is the result of a transfusion reaction caused by mismatched blood. The individual will experience headache and difficulty breathing; the face will appear flushed, and there will be accompanying pain in the neck, chest and lower back. The RBCs will be destroyed, their hemoglobin converted to bilirubin, which accumulates, causing jaundice or yellowing of the skin. The kidneys may fail.
The ABO blood group consists of those individuals who have the presence or absence of two major antigens on the RBC membrane, antigen A and antigen B. Due to inheritance, a person’s RBCs contain only one of four antigen combinations: only A, only B, both A and B or neither A nor B.
Based on these facts, blood is typed. Someone with only antigen A has type A blood. An individual with only antigen B has type B blood. Someone with both antigen A and antigen B has type AB blood. If, however, a person has neither antigen A nor antigen B, then that individual has type O blood.
Antibodies are formed during infancy against the ABO antigens not present in our own RBCs. Individuals with type A blood have antibody anti-B in their plasma; those with type B blood have antibody anti-A; those with type AB blood have neither antibody; finally, those with type O blood have both antibody anti-A and antibody anti-B. An antibody of one type will react with an antigen of the same type and cause agglutination.
Therefore, a person with type A (anti-B) blood must not receive blood of type B or AB. Likewise, a person with type B (anti-A) must not receive type A or AB blood. Similarly, a person with type O (anti-A and anti-B) must not receive type A, B or AB blood. However, a person with type AB blood, which lacks both anti-A and anti-B antibodies, can receive a transfusion of blood of any type and is therefore known as a universal recipient. A person with type O blood lacks antigens A and B and is known as a universal donor, because type O blood could be transfused into people with any of the blood groups.
The Rh blood group was named after the Rhesus monkeys, the animals in which one of the eight Rh antigens or factors was first identified and studied. This was antigen D or agglutinogen D, which was later discovered in humans. If antigen D and other Rh antigens are found on the RBC membrane, the blood is Rh positive. Most Americans are Rh positive. If the RBCs lack the antigens, the blood is Rh negative. The presence or absence of the antigens is an inherited trait.
Unlike the antibodies of the ABO system, anti-Rh antibodies do not develop spontaneously. Instead, they develop only in Rh-negative persons if an Rh-negative person receives a blood transfusion of Rh-positive blood. Shortly after receiving the mismatched Rh-positive blood, the Rh-negative person begins to produce anti-Rh antibodies against the foreign blood. This initial mismatch has no immediate serious consequences because it takes the body time to react and produce antibodies. However, if a second mismatched transfusion occurs, the patient’s antibodies will now attack and rupture the Rh-positive blood donor’s RBCs and they will agglutinate.
A similar problem occurs when an Rh-negative mother carries an Rh-positive baby. This is the case in which the mother is Rh negative and the father is Rh positive. The first pregnancy is usually normal. Because the mother may now be sensitized to the Rh-positive antigens, she will produce anti-Rh positive antibodies in the future.

These antibodies will cross through the placenta and destroy the child’s RBCs, causing a condition known as erythroblastosis fetalis (eh-RITH-roh-blass-TOH-sis fee-TAL-is) or hemolytic disease of the newborn. The baby will be anemic and suffer brain damage due to lack of oxygen to nerve cells. Death may result. However, today this condition is rare. An Rh-negative woman can be given a drug called RhoGAM. This is, in actuality, anti-Rh antibodies that will bind to any Rh positive fetal cells and shield them, thus protecting any of the child’s RBCs that might contact the mother’s cells. This sensitizes her immune system.
A person lacking antigens A and B has blood type O.
If blood groups are mismatched, agglutination, or clumping of red blood cells will occur.
“Give me more O-negative!” shouted the emergency room nurse as they worked frantically on a gunshot wound victim. Why would they give O-negative to a patient whose blood type is unknown? Type O is used because it is the “universal donor”; there are no antigens for any antibodies to react against. Negative is used because there are no antigens for any potential Rh antibodies to attack.
CHAPTER 14
The cardiovascular system consists of the heart and thousands of miles of blood vessels. The heart is the muscular pump that forces the blood through a system of vessels made of arteries, veins and capillaries.
These vessels transport the blood, which carries oxygen, nutrients, hormones, enzymes and cellular waste to and from the trillions of cells that make up our bodies. These cells need oxygen and nutrients from digested food to make the chemical energy (ATP) that allows the cells to function properly. Enzymes assist in the chemical reactions inside the cells, and waste products from these reactions must be transported by the cardiovascular system to sites like the lungs and kidneys for excretion from the body. The force to transport the blood is provided by the cardiac muscle that makes up the bulk of the heart.
The function of transportation of blood by the cardiovascular system occurs 24 hours a day 7 days per week, nonstop for 70, 80 or 90 years or more. This is possible because the heart beats about 72 times a minute. It is a unique organ in that it can contract, rest and immediately contract again during our entire lifetime. The system has a series of valves that prevent blood from backflowing through the blood vessels. It is our pumping heart that helps keep us alive and healthy.
The cardiovascular system consists of the heart, blood vessels
Enzymes assist in the chemical reaction within cells.
Oxygen and nutrients from digested food help make the chemical energy ATP
A disease that results from untreated streptococcal infections, occurring more in children rheumatic heart disease
A disease that results from reduced blood flow in the coronary arteries that supply the myocardium of the heart is called coronary heart disease
Inadequate blood flow to the heart muscle can cause an area of damaged cardiac tissue known as a(n) infarct
The heart is positioned obliquely between the lungs in the mediastinum. About two-thirds of its bulk lies to the left side of the midline of the body. It is shaped like a blunt cone. It is about the size of a closed fist. It is approximately 5 inches long (12 cm), 3.5 inches wide at its broadest point (9 cm) and 2.5 inches thick (6 cm).

It is enclosed in a loose fitting serous membrane known as the pericardial (pair-ih-CAR-dee-al) sac, which can also be referred to as the parietal pericardium. The pericardial sac is made up of two layers.
The outermost layer is the fibrous layer or fibrous pericardium (FYE-bruss pair-ih-CAR-dee-um). It is made of tough fibrous connective tissue and connects to the large blood vessels that enter and leave the heart (the vena cavae, aorta, pulmonary arteries and veins), to the diaphragm muscle and to the inside of the sternal wall of the thorax. It prevents overdistention of the pumping heart by acting as a tough protective membrane surrounding the heart. It also anchors the heart in the mediastinum.
The innermost layer of the pericardial sac is the serous layer or serous pericardium. This layer is thin and delicate. It is continuous with the outermost layer of the wall of the heart, called the epicardium, at the base of the heart. It is also continuous with the large blood vessels of the heart and is known as the parietal layer of the pericardial sac.
The outermost layer of the wall of the heart is called the epicardium (ep-ih-CAR-dee-um) or visceral pericardium. It is a thin, transparent layer composed of serous tissue and mesothelium (a type of epithelial tissue). Because of its serous nature, it can also be called the serous pericardium of the heart. To prevent confusion with the pericardial sac’s innermost layer, we will refer to it as the epicardium
Between the epicardium of the heart and the serous pericardium of the pericardial sac is a space called the pericardial cavity. This cavity contains a watery fluid called the pericardial fluid, which reduces friction and erosion of tissue between these membranes as the heart expands and contracts during a cardiac cycle. If an inflammation of the innermost layer of the pericardial sac develops, it is known as pericarditis.
Because the outermost layer of the heart is the outermost layer of an organ of the body, this epicardium can also be referred to as the visceral peritoneum. Underneath the epicardium is the second layer of the wall of the heart. This makes up the bulk of the heart and is called the myocardium (my-oh-CAR-dee-um). This is the layer of cardiac muscle tissue. Its cells or fibers are involuntary, striated and branched. Refer to Chapter 9 for a review of cardiac tissue anatomy. The tissue of this layer is arranged in interlacing bundles and is the layer responsible for contraction of the heart.
The third or innermost layer of the wall of the heart is called the endocardium (en-doh-CAR-dee-um). It is a thin layer of endothelium (a type of epithelial tissue) that overlies a thin layer of connective tissue penetrated by tiny blood vessels and bundles of smooth muscle. It acts as a lining for the myocardium. It covers the valves of the heart and the chordae tendineae of the valves.
The inside of the heart is divided into four chambers that receive blood from various parts of the body. The two upper chambers are called the right atrium (RITE AY-tree-um) and the left atrium. Each atrium has an external appendage called an auricle (AW-rih-kl), named because of its similarity to the ear of a dog. The auricle increases the volume of the atrium. The lining of each atrium is smooth, except for the anterior atrial walls and the lining of the two auricles, which contain projecting muscle bundles called the musculi (MUSS-kyoo-lye) pectinati (pek-tin-NAY-tye) that give the auricles their rough appearance. The two atria are separated from each other by an internal interatrial septum.
The lower two chambers are called the right ventricle (RITE VEN-trih-kl) and the left ventricle. The two ventricles are separated from one another by an internal interventricular septum. The irregular ridges and folds of the myocardium of the ventricles are called the trabeculae (trah-BEK-yoo-lay) carneae (KAR-neh-ee). The muscle tissue of the atria and ventricles is separated by connective tissue that also forms the valves. This connective tissue divides the myocardium into two separate muscle masses. Externally, a groove called the coronary sulcus (KOR-ah-nair-ee SULL-kus) separates the atria from the ventricles. Two other sulci (plural) are seen externally. The anterior interventricular sulcus and the posterior interventricular sulcus separate the right and left ventricles from one another. The sulci contain a varying amount of fat and coronary blood vessels (vessels that supply the heart tissue with blood).
The right atrium receives blood from all parts of the body except the lungs. It receives this blood through three veins. The superior vena cava, also known as the anterior vena cava, brings blood from the upper parts of the body, the head, neck and arms. The inferior vena cava, also known as the posterior vena cava, brings blood from the lower parts of the body, the legs and abdomen. The coronary sinus drains the blood from most of the vessels that supply the walls of the heart with blood. This blood in the right atrium is then squeezed into the right ventricle.
The right ventricle pumps the blood into the next major vessel, the pulmonary trunk, which splits into the right pulmonary artery and the left pulmonary artery. These arteries each carry the blood to a lung. In the lungs, the blood releases the carbon dioxide it has been carrying and picks up oxygen. The oxygenated blood returns to the heart via four pulmonary veins that empty into the left atrium. The blood is then squeezed into the left ventricle.
The left ventricle pumps the blood into the next great vessel, the ascending aorta. From here the aortic blood goes to the coronary arteries (which supply the walls of the heart with oxygenated blood), the arch of the aorta (which sends arteries to upper parts of the body) and the descending thoracic aorta, which becomes the abdominal aorta. These arteries transport oxygenated blood to all parts of the body.
The size of the chambers and the thickness of the chamber walls vary, due to the amount of blood received and the distance this blood must be pumped. The right atrium, which collects blood coming from all parts of the body except the lungs, is slightly larger than the left atrium, which receives only the blood coming from the lungs. The thickness of the chamber walls varies. Ventricles have thick walls, whereas the atria are thin walled. They are assisted with pumping blood by the reduced pressure caused by the expanding ventricles as they receive the blood. The thickness of the two ventricle walls varies also. The left ventricle has walls thicker than the right ventricle since it must pump the oxygenated blood at high pressure through thousands of miles of blood vessels in the head, trunk and extremities.
The valves of the heart are designed in such a way as to prevent blood from flowing back into the pumping chamber. There are two atrioventricular valves between the atria and their ventricles. The valve between the right atrium and the right ventricle is called the tricuspid (try-KUSS-pid) valve because it consists of three flaps or cusps. These flaps are made of fibrous connective tissue that grows out of the walls of the heart and is covered with endocardium. The pointed ends of the cusps project down into the ventricle. Cords called chordae (KOR-dee) tendineae (TIN-din-ee) connect the pointed ends of the flaps or cusps to small conical projections called the papillary (PAP-ih-layr-ee) muscles located on the inner surface of the ventricle.
The atrioventricular valve between the left atrium and the left ventricle is known as the bicuspid (bye-KUSS-pid) or mitral (MYE-tral) valve. As the name indicates, it has two cusps or flaps, whose pointed ends project down into the ventricle with the same structures as the tricuspid valve. It is the only valve in the heart with only two cusps; all others have three cusps.
The two arteries that leave the heart (the ascending aorta and the pulmonary trunk) also have valves that prevent blood from flowing back into the pumping chamber. These are called the semilunar valves. The pulmonary semilunar valve is found in the opening where the pulmonary trunk exits the right ventricle. The aortic semilunar valve is found in the opening where the ascending aorta leaves the left ventricle. Both of the valves are made of three semilunar cusps that allow blood to flow only in one direction.
Most of the heart is on the left side of the body’s midline.
The membrane surrounding the heart is the pericardial sac
The outer layer of the membrane is the fibrous pericardium , and the inferior inner layer is the serous pericardium.
The outer layer of the heart is the epicardium
The middle layer of the heart is the myocardium.
The inner layer of the heart is the endocardium
The upper chambers of the heart are called the atria
The lower chambers of the heart are called the ventricles
The three veins supplying blood to the right atrium are the superior (or anterior) venae cava and inferior (or posterior) venae cava and the coronary sinus.
In the lungs, blood gives up carbon dioxide and receives oxygen.
The heart muscle is supplied with oxygenated blood by the coronary arteries.
The descending aorta becomes the abdominal aorta.
Of the four heart chambers, the left ventricle has the thickest walls.
The bicuspid (or mitral) valve is between the left atrium and the left ventricle.
All of the valves have three cusps except the bicuspid (or mitral), which has two cusps.
The superior vena cava drains the upper portion of the body, and the inferior vena cava the lower portion.
The two arteries that leave the heart, the ascending aorta, and the pulmonary trunk have valves that prevent blood from flowing back into the pumping chambers, which are known as the semilunar valves
The valve between the right atrium and the right ventricle consists of three flaps, or cusps, and is known as the tricuspid valve
Some popular songs use the phrase “heart strings.” Does your heart actually have heart strings? What is their function? Correct Answer: Yes, they are called chordae tendinae, and they attach to the flaps of the bicuspid and tricuspid valves to keep them from extending into the atria. They are attached to papillary muscles in each ventricle.
As we discuss blood flow through the heart, it is easier to study its path by beginning at one point, going in a one-way direction and ending at the same point we began. We will do this, but remember, the heart actually pumps the blood in a slightly different manner. That is, the two atria contract simultaneously, while the two ventricles relax. Then the two ventricles contract simultaneously, while the two atria relax. Then all chambers rest before the cycle begins again.
Deoxygenated blood (blood high in carbon dioxide) returns from the upper portions of the body through the superior or anterior vena cava and from the lower portions of the body through the inferior or posterior vena cava to the right atrium of the heart. The blood is then squeezed by contraction of the right atrium through the tricuspid valve into the right ventricle. As the right ventricle contracts, it pumps the blood through the pulmonary semilunar valve into the pulmonary trunk, which branches into the right pulmonary artery that goes to the right lung and the left pulmonary artery that goes to the left lung. In the alveoli of the lungs surrounded by capillaries, the blood loses the carbon dioxide and picks up oxygen.
Deoxygenated blood looks dark; hence, veins are usually depicted in textbooks as blue. Oxygenated blood looks bright red; hence, arteries are usually shown in red in textbooks. The oxygenated blood returns to the left atrium of the heart through four pulmonary veins. When the left atrium contracts, it squeezes the blood through the bicuspid or mitral valve into the left ventricle. As this ventricle with its thick muscular walls contracts, it pushes the blood through the aortic semilunar valve into the ascending aorta. The ascending aorta distributes the oxygenated blood to all parts of the body.

The heart is innervated by the autonomic nervous system. However, it does not initiate a contraction but only increases or decreases the time it takes to complete a cardiac cycle. This is made possible because the heart has its own intrinsic regulating system called the conduction system that generates and distributes electrical impulses over the heart to stimulate cardiac muscle fibers or cells to contract.
The system begins at the sinoatrial (sigh-no-AY-tree-al) node, known as the SA node or pacemaker, which initiates each cardiac cycle and sets the pace for the heart rate. It is located in the superior wall of the right atrium. It can be modified by nerve impulses from the autonomic nervous system; sympathetic impulses will speed it up, and parasympathetic impulses will restore or slow it down. Thyroid hormone and epinephrine carried by the blood will also affect the pacemaker. Once an impulse is initiated by the SA node, the impulse spreads out over both atria, causing them to contract simultaneously. At the same time, it depolarizes the atrioventricular (AY-tree-oh-vin-TRIK-yoo-lar) (AV) node. It is located in the lower portion of the right atrium.
From the AV node, a tract of conducting fibers called the atrioventricular bundle or bundle of His (BUN-dull of HIZ) runs through the cardiac mass to the top of the interventricular septum. It then branches and continues down both sides of the septum as the right and left bundle branches. Thus the bundle of His distributes the electrical charge over the medial surfaces of the ventricles. The actual contraction of the ventricles is stimulated by the Purkinje’s (pur-KIN-jeez) fibers (also known as the conduction myofibers) that emerge from the bundle branches and pass into the cells of the myocardium of the ventricles.
In a normal heartbeat, the two atria contract simultaneously while the two ventricles relax. Then, when the two ventricles contract, the two atria relax. Systole (SIS-toh-lee) is the term used to refer to a phase of contraction and diastole (dye-ASS-toh-lee) is the term for a phase of relaxation. A cardiac cycle or complete heartbeat, therefore, consists of the systole and diastole of both atria and the systole and diastole of both ventricles. The pressure developed in a heart chamber is related to the chamber size and the volume of blood it contains. The greater the volume of blood, the higher the pressure.
The average heart beats approximately 72 times per minute. Therefore, we will assume that each cardiac cycle requires about 0.8 second. During the first 0.1 second, the atria contract and the ventricles relax. The atrioventricular valves (the bicuspid and tricuspid) are open and the semilunar valves (aortic and pulmonary) are closed. During the next 0.3 second, the atria are relaxing and the ventricles are contracting. During the first part of this period, all valves are closed to help build pressure. During the second part of this period, the semilunars are open.
The last 0.4 second of the cycle is the relaxation or quiescent period. All chambers are in diastole. So for a full one-half period of a cycle, the heart muscle is resting. For the first part of this period all valves are closed. During the latter half, the tricuspid and bicuspid valves open to allow blood to start draining into the ventricles.
The systemic circulation route includes all of the oxygenated blood that leaves the left ventricle of the heart through the aortic semilunar valve and goes to the aorta and the deoxygenated blood that returns to the right atrium of the heart via the superior and inferior vena cavae after traveling to all the organs of the body, including the nutrient arteries to the lungs. There are many subdivisions of this route. Systemic refers to the fact that it is carrying blood to all organs of all the systems of the body.

Two of its significant subdivisions are the coronary circulation and the hepatic portal circulation routes. The coronary circulation route supplies the myocardium of the heart. The hepatic portal circulation route travels back and forth from the intestine of the digestive tract to the liver. This route is used to store excess sugars from digestion into the liver after a meal and to release sugars stored in the liver as glycogen between meals to maintain blood glucose levels.
The pulmonary circulation is the route that goes from the right ventricle of the heart through the pulmonary semilunar valve to the pulmonary trunk that branches into the right and left pulmonary arteries, which go to the lungs. Here the deoxygenated blood loses its carbon dioxide and picks up the oxygen and returns to the left atrium of the heart via the four pulmonary veins.
The cerebral circulation is the blood circulatory route that supplies the brain with oxygen and nutrients and disposes of waste.
The fetal circulation, a temporary circulation, is the circulation route that exists only between the developing fetus and its mother. It contains special structures that allow the fetus to exchange oxygen and nutrients with its mother and to get rid of fetal waste products through this connection.
Deoxygenated blood is dark red, whereas oxygenated blood is bright red
The conduction system of the heart is actually a(n) electrical system.
The atrioventricular bundle is also known as the bundle of His
Regulation of the beats of the heart reside in the autonomic nervous system.
Contraction of the heart is the systole, and the relaxation phase is the diastole.
Blood supply to the heart is via the coronary circulation route.
Fetal circulation is a temporary circulation route that exists only between the developing fetus and its mother.
The sinoatrial, or S-A, node initiates each cardiac cycle and sets the pace for the heart rate and is also called the pacemaker
One complete heartbeat consists of the systole and diastole of both atria and the systole and diastole of both ventricles and is known as a(n) cardiac cycle
The circulation of blood to all organs of all the systems of the body is known as systemic circulation
Deoxygenated blood loses its carbon dioxide gas in the lungs, picks up the oxygen gas, and returns to the left atrium of the heart via the four pulmonary veins in a circulation route called pulmonary circulation

Blood vessels can be categorized into: 1. arteries 2. arterioles 3. veins 4. venules 5. capillaries
Arteries and veins have walls composed of three layers: 1. the tunica intima (TYOO-nih-kah IN-tih-mah) composed of a single layer of endothelial cells; 2. the tunica media made of smooth muscle; 3. and the tunica adventit

Arteries have walls made of these three coats or tunics surrounding a hollow core known as a lumen (LOO-men) through which blood flows. Arteries are thicker and stronger than veins with two major properties: elasticity and contractility. This is necessary because when the two ventricles of the heart contract, they inject a large amount of blood into the large aorta and pulmonary trunk. These arteries must be able to expand to accommodate the extra blood. Then while the ventricles relax, the elastic recoil of the arteries pushes the blood forward.
Most parts of our body receive branches from more than one artery. In these areas, the distal ends of these branches unite to form one artery going into the organ. The junction of two or more blood vessels is called an anastomosis (ah-nas-toh-MOH-sis).
Arterioles (ar-TEE-ree-olz) are small arteries that deliver blood to capillaries.
Capillaries (CAP-ih-lair-eez) are microscopic vessels made of simple squamous epithelial cells, one cell layer thick called endothelium. They are found in close proximity to nearly every cell of the body. They connect arterioles with venules. Their primary critical function is to permit the exchange of nutrients and oxygen and waste and carbon dioxide between the blood and the tissue cells of the body. Their unique wall structure of a single cell layer allows this to occur by diffusion. A substance in the blood must pass through the plasma membrane of just one cell to reach the tissue cell and vice versa. This vital exchange occurs only through capillary walls.

Venules (VIN-yoolz) are small vessels that connect capillaries to veins. They collect blood from capillaries and drain it into veins.
Veins are made of the same three coats or tunics as arteries but have less elastic tissue and smooth muscle but more white fibrous connective tissue in the outer layer or adventitia. They also are capable of distention to adapt to variations of blood volume and blood pressure. Veins also contain valves that ensure blood flow in one direction, toward the heart.
There is another term that will be encountered when reading about blood vessels. That term is vascular or venous sinuses. These should not be confused with cavities in bones, which are also called sinuses. Venous sinuses are veins with thin walls.
The aorta is the largest artery in the body. It begins as it exits from the left ventricle of the heart as the ascending aorta. It then arches to the left as the arch of the aorta (or aortic arch) and heads down along the spine through the thorax as the thoracic aorta. When it passes through the diaphragm muscle and enters the abdominal cavity, it is called the abdominal aorta. It is as thick as a finger and its branches go to various regions of the body. Its arterial branches are usually named according to the region of the body, the organ it goes to, or the bone it follows.
The right and left coronary arteries branch off the ascending aorta and supply the heart.
The first branch of the aortic arch is the brachiocephalic artery, which divides into the right common carotid artery, which transports blood to the right side of the head and neck, and the right subclavian artery, which transports blood to the upper right limb.
The second branch of the aortic arch is the left common carotid artery, which divides into the left internal carotid artery that supplies the brain and the left external carotid artery that supplies muscles and skin of the neck and head.
The third branch of the aortic arch is the left subclavian artery, which branches into the vertebral artery that supplies part of the brain. In the axillary area of the body, the subclavian artery is now known as the axillary artery, which continues down the arm as the brachial artery. Near the elbow joint it divides into the radial and ulnar arteries, which supply the forearm.
There are 10 pairs of intercostal arteries that supply muscles of the thorax. Bronchial arteries supply the two lungs, esophageal arteries go to the esophagus, and phrenic arteries supply the diaphragm muscle.
The first branch is the celiac trunk, which has three branches: 1. the left gastric artery, which goes to the stomach; 2. the splenic artery, which supplies the spleen; 3. and the common hepatic artery, which goes to the liver. The superior mesenteric artery supplies the small intestine and the colon. | | 4. | The right and left renal arteries go to the kidneys. | | | 5. | The right and left gonadal (ovarian in female and testicular in males) arteries serve the gonads. | | | 6. | The lumbar arteries are several pairs that go to the muscles of the abdomen and walls of the trunk of the body. |
The right and left common iliac artery is the final branch of the abdominal aorta. Each divides into an internal iliac artery, which goes to the thigh. Here it is called the femoral artery and its branch is called the deep femoral artery, which supplies the thigh with blood. At the knee, the femoral artery is now called the popliteal artery, which divides into the anterior and posterior tibial arteries, which supply the leg and foot. The anterior tibial artery then terminates as the dorsalis pedis artery, which supplies the dorsal part of the foot.
Most of the arteries of the body are in deep and protected areas of the body. Veins, however, tend to be closer to the body surface and are easily seen through the skin. Deeper veins follow the courses of the major arteries and their names are identical to the arteries. Veins converge on either the superior or inferior vena cava. Veins draining the head and arms merge into the superior vena cava; those draining the lower parts of the body merge into the inferior vena cava. The radial and ulnar veins, which drain the forearm, unite to form the brachial vein, which drains the arm and empties into the axillary vein in the armpit area. | |

| The cephalic vein drains the lateral part of the arm and connects into the axillary vein. | | |

| The basilic vein drains the medial part of the arm and joins the brachial vein. The basilic and brachial veins are joined near the elbow by the median cubital vein. It is this vein that is usually used for drawing blood. |
The subclavian vein drains blood from the arm via the axillary vein and drains blood from the muscles and skin of the head region via the external jugular vein. The vertebral vein drains the back of the head. | |

| The internal jugular vein also drains the dural sinus of the brain in the head. | | |

| The right and left brachiocephalic veins are large veins that receive blood from the subclavian, vertebral, and internal jugular veins. It then joins the superior vena cava. |
The azygos vein drains the thorax and also merges with the superior vena cava just before it enters the heart.
The anterior and posterior tibial veins and the peroneal vein drain the calf and the foot. The posterior tibial vein is called the popliteal vein at the knee and the femoral vein in the thigh. The femoral vein is called the external iliac vein as it goes into the pelvis.
The great saphenous veins are the longest veins of the body. They drain the superficial aspects of the leg and begin as the dorsal venous arch in the foot and eventually merge with the femoral vein in the thigh. | The right and left common iliac veins are formed by the union of the external and internal iliac veins. These drain the pelvis. The common iliac veins unite to form the inferior vena cava in the abdominal cavity. | | |

| The right and left gonadal veins drain the gonads and eventually join the left renal vein. | | |

| The right and left renal veins drain the kidneys. | | |

| The hepatic portal vein drains the organs of the digestive tract and goes to the liver. |
The right and left hepatic veins drain the liver.
The three layers of blood vessels are the intima (outer), media (middle) and adventitia (outer) tunicae.
Arterioles are small arteries
Venules are small veins
Capillaries are vessels consisting of a single cell layer
The first branch of the aortic arch is the brachiocephalic artery.
The carotid arteries supply the head, neck and brain.
Arterioles are small arteries that deliver blood to capillaries.
The junction of two or more blood vessels is called a(n) anastomosis
Arteries have walls made of three coats or tunics surrounding a hollow core known as a lumen
The longest veins of the body, which drain the superficial aspects of the leg, are known as the great saphenous veins
Dorie is checking on her patients after surgery. She checks each patient’s pulse at several points on the body. What vessel would she be palpating on the top of the foot? Dorsalis venous arch
Tavis and Murdock are studying a circulatory model. “The blue ones are always veins,” says Tavis. “Except for the vessel that runs to the lungs,” says Murdock. Which vessel would that be? Pulmonary artery
Integumentary System 1. Blood flow to the skin aids in temperature control for the body. 2. Blood flow to the skin brings oxygen and nutrients to and removes waste from skin tissue and glands. 3. Dilation of blood vessels in the dermis occurs when we are embarrassed, resulting in blushing seen in light-skinned individuals.

Skeletal System 1. Bones store and release calcium to maintain plasma levels of calcium. 2. Bones are the sites of hematopoiesis. 3. Bones (sternum and ribs) protect the cardiovascular organs.

Muscular System 1. Exercising muscles receive increased blood flow delivering oxygen and nutrients and removing waste. 2. Cardiac and smooth muscle contractions maintain blood flow and blood pressure. 3. Exercise helps prevent cardiovascular disease.

Nervous System 1. The brain and spinal cord depend on blood flow for survival and maximum function. 2. The autonomic nervous system regulates heartbeat rate and blood pressure.

Endocrine System 1. The bloodstream transports hormones to their target organs. 2. Epinephrine, thyroxine and antiduretic hormone affect blood pressure rates.

Lymphatic System 1. The lymphatic system drains and returns interstitial fluids back to the bloodstream. 2. Blood transports lymphocytes and antibodies. 3. The immune system protects the heart and blood vessels from foreign microbes.

Digestive System 1. The digestive system breaks down food and nutrients into forms that can be absorbed and transported by the bloodstream. 2. Iron and the B vitamins are provided by the digestive system for red blood cell formation.

Respiratory System 1. The respiratory system provides lungs for the exchange of oxygen and carbon dioxide with the red blood cells. 2. Respiratory movements aid in venous blood return to the heart.

Urinary System 1. The kidneys filter the blood of wastes, excess electrolytes and water. 2. The kidneys help control blood volume and blood pressure. 3. Blood pressure helps maintain kidney function.

Reproductive System 1. Increases in blood volume to the penis maintains an erection. 2. Estrogen maintains vascular health in females.

CHAPTER 15
The lymphatic system is intimately associated with the blood and the cardiovascular system. Both systems transport vital fluids throughout the body, and both have a system of vessels that transport these fluids. The lymphatic system transports a fluid called lymph through special vessels called lymph capillaries and lymphatics. This lymph eventually gets returned to the blood from where it originated.
In addition to fluid control, our lymphatic system is essential to helping us control and destroy a large number of microorganisms that can invade our bodies and cause disease and even death. The lymphatic system consists of lymph, lymph vessels, lymph nodes and four organs. The organs are the tonsils, the spleen, the thymus gland and Peyer’s patches.
The primary function of this system is to drain from tissue spaces, protein-containing fluid that escapes from the blood capillaries. Other functions are to transport fats from the digestive tract to the blood, to produce lymphocytes and to develop immunities.
In our bodies where blood capillaries are close to the cells of tissues, the blood pressure in the cardiovascular system forces some of the plasma of blood through the single-celled capillary walls. When this plasma moves out of the capillaries and into the spaces between tissue cells, it gets another name and is called interstitial (in-ter-STISH-al) fluid. Most, but not all, of this fluid gets reabsorbed into the capillary by differences in osmotic pressure.
However, some does not, and this interstitial fluid must be drained from the tissue spaces to prevent swelling or edema (eh-DEE-mah) from occurring. It is the role of the lymphatic capillaries to drain this fluid. Once the interstitial fluid enters a lymphatic capillary, it gets a third name and is now called lymph (LIMF).
In the villi of the small intestine, there are special lymphatic vessels called lacteals (LACK-teelz) whose role is to absorb fats and transport them from the digestive tract to the blood. Fats from the intestine travel through the lymphatic system, which delivers them to the blood, when the lymph rejoins the blood at the right and left subclavian veins. Lymph in the lacteals looks milky because of the fat content and is called chyle (KYLE).

Lymphatic vessels originate as blind-end tubes that begin in spaces between cells in most parts of the body. The tubes, which are closed at one end, occur singly or in extensive plexuses and are called lymph capillaries. These vessels are not found in the central nervous system, red bone marrow, vascular tissue or portions of the spleen. Lymph capillaries are much larger and more permeable than blood capillaries. Lymph capillaries will eventually unite to form larger and larger lymph vessels called lymphatics (LIM-fat-iks). Lymphatics resemble veins in structure but have thinner walls and more valves. The large number of valves helps to ensure that the lymph will not backflow but go in one direction only. Along lymphatics there are lymph nodes found at various intervals. | |

| Lymphatics of the skin travel in loose subcutaneous connective tissue and generally follow the routes of veins. Lymphatics of the viscera generally follow the routes of arteries and form plexuses around the arteries. Eventually, all the lymphatics of the body converge into one of two main channels: either the thoracic duct (the main collecting channel), also known as the left lymphatic duct, or the right lymphatic duc |
Lymph nodes are oval to bean-shaped structures found along the length of lymphatics . They are also known as lymph glands. They range in size from 1 to 25 mm in length (about 0.04 to 1 inch), looking like small seeds or almonds. The three regions of aggregations of nodes in the body are the groin, armpits and neck. A lymph node contains a slight depression on one side called the hilum (HIGH-lum) where efferent (EE-fair-ent) lymphatic vessels leave and a nodal artery enters and a nodal vein leaves the node.
Each lymph node or gland is covered by a capsule of fibrous connective tissue that extends into the node. These capsular extensions are called trabeculae (trah-BEK-yoo-lay). The capsular extensions divide the lymph node internally into a series of compartments that contain lymphatic sinuses and lymphatic tissue. Lymphatic vessels that enter the lymph node at various sites are called afferent (AFF-er-ent) lymphatic vessels.
The lymphatic tissue of the node consists of different kinds of lymphocytes and other cells that make up dense aggregations of tissue called cortical or lymph nodules. The lymph nodule surrounds a germinal center that produces lymphocytes.

Lymph sinuses are spaces between these groups of lymphatic tissue. They contain a network of fibers and the macrophage cells. The capsule, trabeculae and hilum make up the stroma or framework of the lymph node.
As lymph enters the node through the afferent lymphatics, the immune response is activated. Any microorganisms or foreign substances in the lymph stimulate the germinal centers to produce lymphocytes, which are then released into the lymph. Eventually, they reach the blood and produce antibodies against the microorganisms. The macrophages will remove the dead microorganisms and foreign substances by phagocytosis.
The four organs of the lymph system are the tonsils, spleen, thymus and the Peyer’s patches.
Interstitial fluid is plasma forced from capillaries.
Edema is another name for swelling. lymph is interstitial fluid that has entered a lymphatic capillary.
Chyle looks milky because of its fat content.
The larger lymph vessels are the lymphatics
The larger lymph vessels of the viscera generally follow the routes of arteries.
Efferent lymphatic vessels leave the lymph nodes at the hilum.
Trabeculae are capsular extensions
Those vessels entering a lymph node are the afferent lymphatic vessels.
The lymph nodule surrounds a germinal center, which produces lymphocytes.
The stroma of a lymph node is made up of the capsule, the trabeculae and the hilum
In the lymph node, any microorganisms or foreign substances stimulate the germinal centers to produce lymphocytes, thereby activating a(n) immune response.
A chronic condition of the lymphatic system caused by a filarial worm invasion resulting in tremendous swelling of the arms or legs is known as elephantiasis
A condition of the lymphatic system that is evidenced by inflammation of the lymphatic vessels with accompanying red streaks visible in the skin is called lymphangitis
Special lymphatic vessels that absorb fats and transport them from the digestive tract to the blood are called lacteals
Patrick has had a sore throat for two days. Now he notices a tender lump just under his right jaw. What could that lump be? Should he be rushing to the hospital? The lump is likely a swollen lymph gland indicating some type of infection. There is probably no need to rush to the hospital, but a visit to the doctor couldn’t hurt, especially if this is a bacterial infection. The doctor can give antibiotics. If the infection is viral, antibiotics will have no effect.
As the plasma of blood is filtered by the blood capillaries, it passes into the interstitial spaces between tissue cells and is now known as interstitial fluid. When this fluid passes from the interstitial spaces into the lymph capillaries, it is called lymph. Lymph is primarily water but it also contains plasma solutes such as ions, gases, nutrients and some proteins and substances from tissue cells such as hormones, enzymes and waste products.
The lymph, drained by the lymphatic capillaries and the lymph plexuses, is then passed to the lymphatic vessels that have a beaded appearance due to the one-way valves that prevent backflow movement. The lymphatics head toward lymph nodes. At the lymph nodes, afferent vessels penetrate the capsules at various positions on the node and the lymph passes through the sinuses of the nodes. In the node, antigenic microorganisms, foreign substances or cancer cells stimulate lymphocytes to divide, and the immune response is activated. Macrophages phagocytize the attacked foreign substances.
Efferent vessels leave nodes and pass on to other lymph nodes by either going with other afferent vessels into another node of the same group or passing on to another group of nodes. The efferent vessels will eventually unite to form lymph trunks.
This circulation of lymph through the various lymphatic vessels is maintained by normal skeletal muscle contractions. This action compresses the lymph vessels and because those vessels have one-way valves, the compression forces the lymph in one direction toward the subclavian veins. Normal movement helps circulate the lymph. Another factor in lymph circulation is respiratory or breathing movements, which cause pressure changes in the thorax. Finally, smooth muscle contraction in the lymphatic vessel also pushes lymph along. However, if lymphatics become obstructed by blockage, then an excessive amount of interstitial fluid will develop in tissue spaces and result in swelling or edema.
Eventually, the efferent lymphatic vessels unite to form lymph trunks. The principal lymphatic trunks of the body are: the lumbar trunk, the intestinal trunk, the bronchomediastinal (brong-koh-mee-dee-ass-TYE-nal) trunk, the intercostal trunk, the subclavian (sub-KLAY-vee-an) trunk and the jugular trunk.
The lumbar trunk drains lymph from the lower extremities, the walls and viscera of the pelvis, the kidneys and adrenal glands and most of the abdominal wall. The intestinal trunk drains lymph from the stomach, intestines, pancreas, spleen and the surface of the liver. The bronchomediastinal trunk drains the thorax, lungs, heart, diaphragm and the rest of the liver. The intercostal trunk also helps drain lymph from portions of the thorax. The subclavian trunk drains the upper extremities, that is, arms, hands and fingers. Finally, the jugular trunk drains the head and neck.
These principal trunks now pass their lymph into two main channels: the thoracic duct, which is the main collecting duct of the system and is also known as the left lymphatic duct, and the right lymphatic duct. Ultimately, the thoracic duct empties all of its lymph into the left subclavian vein and the right lymphatic duct empties all of its lymph into the right subclavian vein, so the journey of the lymph is now completed. The lymph is drained back into the blood where it originally came from, and the cycle completes itself. This circulation repeats itself continuously, thus maintaining the proper levels of lymph, plasma and interstitial fluids in the body.
Lymph trunks are formed by uniting efferent vessels.
The principal trunks pass their lymph into the thoracic duct and the right lymphatic duct.
The lymph flow cycle is completed when the lymph is drained back into the Skeletal muscle contraction.
The lymphatic system has four organs: 1. tonsils 2. spleen 3. thymus gland 4. Peyer’s patches.
Tonsils are masses of lymphoid tissue embedded in mucous membrane. There are three groups of tonsils. The palatine (PAL-ah-tyne) tonsils are the ones commonly removed in a tonsillectomy. They are located in the tonsillar fossae between the pharyngopalatine and glossopalatine arches on each side of the posterior opening of the oral cavity. The pharyngeal (fair-in-JEE-al) tonsils are also known as the adenoids (ADD-eh-noydz). They are located close to the internal opening of the nasal cavity. When they become swollen, they can interfere with breathing. The lingual (LING-gwall) tonsils are located on the back surface of the tongue at its base.
In these positions, the tonsils form a protective ring of reticuloendothelial cells against harmful microorganisms that might enter the nose or oral cavity. Occasionally, they become chronically infected and need to be removed. However, this operation is not as common as it once was because of the understanding of how important these organs are in protecting the body and as being part of the immune system. Tonsils are more functional in children. As we age, the tonsils decrease in size and may even disappear in some individuals.
The spleen (SPLEEN) is oval in shape and is the single largest mass of lymphatic tissue in the body. It measures about 12 cm, or 5 inches, in length. It is found in the left upper corner of the abdominal cavity. It filters blood via the splenic artery and splenic vein, which enter the spleen at a slightly concave border called the hilum. The spleen phagocytizes bacteria and worn-out platelets and red blood cells. This action releases hemoglobin to be recycled. It also produces lymphocytes and plasma cells. The spleen stores blood and functions as a blood reservoir. During a hemorrhage, the spleen releases blood into the blood circulation route. Serious injury to the spleen may require its removal.
The thymus gland is a bilobed mass of tissue located in the mediastinum along the trachea behind the sternum. Its role in the endocrine system is discussed in Chapter 12. It reaches maximum size during puberty and then decreases. In older individuals, the thymus becomes small and is difficult to detect because it is replaced with fat and connective tissue. It is involved in immunity. The thymus is a site for lymphocyte production and maturation. The thymus helps develop T lymphocytes in the fetus and in infants for a few months after birth. A number of its lymphocytes degenerate, but those that mature leave the thymus and enter the blood to travel to other lymphatic tissues where they protect against foreign substances and harmful microorganisms.
Peyer’s (PIE-erz) patches (also known as aggregated lymphatic follicles) are found in the wall of the small intestine. They resemble tonsils. Their macrophages destroy bacteria. Bacteria are always present in large numbers in the intestine, and the macrophages prevent the bacteria from infecting and penetrating the walls of the intestine.
The palatine tonsils are the ones commonly removed in a tonsillectomy.
The adenoids are the pharyngeal tonsils.
The spleen phagotytizes bacteria and worn-out platelets and red blood cells releasing hemoglobin.
Peyer’s patches are found in the wall of the small intestine.
The macrophages of the Peyer’s patches destroy bacteria.
Aggregated lymphatic follicles found in the wall of the small intestine that resemble tonsils are known as Peyer's patches.
The bilobed mass of tissue located in the mediastinum along the trachea behind the sternum that is involved in immunity is known as the thymus gland
The single largest mass of lymphatic tissue in the body is the spleen
Immunity (im-YOO-nih-tee) is the ability of the body to resist infection from disease-causing microorganisms or pathogens (PATH-oh-jenz), damage from foreign substances and harmful chemicals. Humoral immunity and cellular immunity are the results of the body’s lymphoid tissue. The bulk of our lymphoid tissue is located in the lymph nodes. However, as mentioned, it is also found in the spleen, the tonsils, in the small intestine and, to a lesser extent, in red bone marrow. This lymphoid tissue consists primarily of lymphocytes that can be categorized into two broad groups of cells: the B lymphocytes and the T lymphocytes.
The B lymphocytes are the cells that produce antibodies, and they provide humoral immunity. This type of immunity is particularly effective against circulating bacterial and viral infections. The B cells produce the circulating antibodies that attack the invading agent. B lymphocytes that enter tissues become specialized cells called plasma cells.
The T lymphocytes are responsible for providing cellular immunity. These cells come from the thymus gland, where immunologic competence is conferred on the T lymphocytes around birth. This type of immunity is particularly effective against fungi, parasites, intracellular (inside the cell) viral infections, cancer cells and foreign tissue implants.
Antigens (AN-tih-jenz) are foreign proteins that gain access to our bodies via cuts and scrapes, through the digestive or circulatory systems or through the urinary and reproductive systems. They cause the immune system to produce high molecular weight proteins, called antibodies or immunoglobulins (im-yoo-noh-GLOB-yoo-linz), to destroy the foreign invader.
These foreign proteins can be the flagella or cell membranes of protozoans, the flagella or cell membrane of bacteria, the protein coat of a virus or the surface of a fungal spore. The B lymphocyte and the plasma cell recognize these antigens and produce antibodies that bind with the specific antigen. This binding causes the foreign cells to agglutinate (stick together) and precipitate within the circulatory system or tissues. Then the phagocytic white blood cells come along and eat them up by phagocytosis, eliminating them from the body. Thus, we have an internal defense system to protect us from foreign microbes. Antibodies are formed in response to an enormous number of antigens.
Antibodies have a basic structure consisting of four amino acid chains linked together by disulfide bonds. Two of the chains are identical with about 400 amino acids and are called the heavy chains; the other two chains are half as long, identical and are called the light chains. When united, the antibody molecule is made of two identical halves, each with a heavy and light chain. The molecule has a Y shape and the tips of the Y are the antigen-binding sites. The binding site varies, thus allowing the antibody to bind with the enormous number of antigens. The stem of the Y is always constant.
Five types of antibodies make up the gamma globulins of plasma proteins. Immunoglobulin G (IgG) is found in tissue fluids and plasma. It attacks viruses, bacteria and toxins. It also activates complement, a set of enzymes that attack foreign antigens. Immunoglobulin A (IgA) is found in exocrine gland secretions, nasal fluid, tears, gastric and intestinal juice, bile, breast milk and urine. Immunoglobulin M (IgM) develops in blood plasma as a response to bacteria or antigens in food. Immunoglobulin D (IgD) is found on the surface of B lymphocytes and is important in B cell activation. Immunoglobulin E (IgE) is also found in exocrine gland secretions and is associated with allergic reactions, attacking allergy-causing antigens. The most abundant antibodies are IgG, IgA and IgM.
When B lymphocytes come in contact with antigens and produce antibodies against them, this is called active immunity. It can be acquired naturally, as when we are exposed to a bacterial or viral infection, or it can be acquired artificially, as when we receive a vaccine. A vaccine contains either killed pathogens or live, but very weak pathogens. It does not matter whether the antigen is introduced to the body on its own or through a vaccine, the immune response is the same.
The advantage of vaccines is that we do not experience the major symptoms of the disease, which would occur in the primary response to the pathogen, and the weakened antigen stimulates antibody production and immunologic memory. Future exposure keeps us immune to the pathogen. Vaccines are currently available against measles, smallpox, polio, tetanus, chickenpox, pneumonia, diphtheria and various strains of flu.
Passive immunity can be conferred naturally when a fetus receives its mother’s antibodies through the placenta and they become part of the fetal circulatory route. This immunity lasts for several months after birth. Passive immunity can be conferred artificially by receiving gamma globulin, breast milk or immune serum. This is used after exposure to hepatitis. These donated antibodies provide immediate protection, but it only lasts 2 to 3 weeks. Other immune serums include antivenom for snakebites or botulism and rabies serum.
Like the B lymphocytes, T lymphocytes are activated to form clones by binding with an antigen. But T cells are not able to bind with free antigens. The antigens must first be engulfed by macrophages, processed internally and then displayed on their surface to the T cells. Thus, antigen presentation is a major role for macrophages and is absolutely necessary for activation and clonal response of the T cells.
Disease-causing microorganisms are called pathogens.
The B lymphocytes produce antibodies and provide humoral immunity, which is effective against circulating bacterial and viral infections.
The T lymphocytes are responsible for providing cellular immunity, which is effective against fungi, parasites, intracellular viral infections, cancer cells, and foreign tissue implants.
The ability of the body to resist infection from disease-causing microorganisms or pathogens, damage from foreign substances, and harmful chemicals is known as immunity
High molecular weight proteins are called antibodies or immunoglobulins
The body’s production of antibodies against an antigen is active immunity.
The type of immunity received by the fetus from the mother is passive
Antibodies are high molecular weight proteins produced by the immune system to destroy the invading antigens.
Foreign proteins that gain access to our bodies via cuts and scrapes, through the digestive or circulatory systems, or through the urinary and reproductive systems are called antigens
Immunity that can be acquired naturally, as when we are exposed to a bacterial or viral infection, or that can be acquired artificially, as when we receive a vaccine, is known as which type of immunity? Active
Immunity that can be conferred artificially by receiving gamma globulin or immune serum is known as passive immunity
Samantha just went to the clinic for an annual flu shot. Vaccinations (like the flu shot) provide what type of immunity? Active immunity—your body still has to form the antibodies to fight that particular strain.

The lymphocytes of the body are the precursors of a whole range of cells that are involved in the immune response. The following is a list of those cells and their functions. 1. B cells 2. Plasma cells 3. Helper T cells 4. Killer T cells 5. Suppresor T cells 6. Memory cells 7. Macrophages
B cells are lymphocytes found in the lymph nodes, spleen and other lymphoid tissue where they replicate, induced by antigen-binding activities. Their clones or progeny form plasma cells and memory cells.
Plasma cells are formed by replicating B cells, and produce huge numbers of the same antibody or immunoglobulin.
Helper T cells are T cells that bind with specific antigens presented by macrophages. They stimulate the production of killer T cells and more B cells to fight the invading pathogen. They release lymphokines.
Killer T cells kill virus-invaded body cells and cancerous body cells. They are also involved in graft rejections.
Suppressor T cells slow down the activities of B and T cells once the infection is controlled.
Memory cells are descendents of activated T and B cells produced during an initial immune response. They will exist in the body for years, enabling it to respond quickly to any future infections by the same pathogen.
Macrophages engulf and digest antigens. They then present parts of these antigens in their cell membranes for recognition by T cells. This antigen-presentation function is crucial for normal T-cell responses.
In addition to these cells, certain chemicals are produced in the immune response that also help keep us healthy. The lymphokines (LIM-foh-kynz) are chemicals released by the sensitized T lymphocytes. There are a number of these chemicals. Chemotactic factors attract neutrophils, basophils and eosinophils to the infected area. Macrophage migration-inhibiting factor (MIF) keeps macrophages in the local area of infection and inflammation. Helper factors stimulate plasma cells to produce antibodies. Interleukin-2 stimulates proliferation of T and B cells. Gamma interferon helps make tissue cells resistant to viruses, activates macrophages and causes killer T cells to mature. Perforin causes cells to break down. Suppressor factors suppress antibody formation by T cells.

Activated macrophages also release chemicals called monokines (MON-oh-kynz). One is interleukin-1, which stimulates T cell proliferation and causes fever. The body produces fever or elevated temperatures as a response to attempt to kill the invading pathogen. The other is tumor necrosis factor (TNF), which kills tumor cells and attracts the granular leukocytes to the area. Blood-borne proteins, called complement, cause the breakdown or lysis of microorganisms and enhances the inflammatory response.

In addition to these cellular and chemical barriers inside the body, the body has an external covering and other protective mechanisms. The skin’s epidermis is a mechanical barrier to pathogens and toxins. It also has a so-called acid mantle that inhibits bacterial growth. Sebum from the sebaceous glands has antifungal and antibacterial qualities. Tears from the lacrimal gland and saliva contain lysozyme, which destroys bacteria. Mucous membranes lining the digestive, respiratory, urinary and reproductive tracts trap microorganisms and dust and prevent them from entering the circulatory system.
In the nose and throat, the mucus-dust package is brought up to the throat to be swallowed by the action of cilia on the free edge of the epithelial tissue. The hydrochloric acid in the stomach then destroys most pathogens. Even the hairs in our nose have a role to trap large particles and filter them out before they enter the respiratory system.
Killer T cells destroy virus-invaded body cells.
Macrophages engulf antigens, process them internally, and then display the antigens on their surface for recognition by T cells.
Helper T cells stimulate the production of killer T cells and more B cells to fight invading pathogens, and they release chemicals known as lymphokines, which help to keep us healthy.
Cells that are descendants of activated T and B cells produced during an initial immune response, which exist in the body for years, enabling it to respond quickly to any future infections, are known as memory cells
Cells that engulf and digest antigens are called macrophages

Integumentary System 1. The skin’s epidermis is a mechanical barrier to microorganisms. 2. The acid pH mantle of the skin inhibits the growth of most bacteria. 3. Sebum, produced by the sebaceous glands of the skin, has antifungal properties. 4. Lymphatic vessels drain interstitial fluid from the dermis of the skin preventing edema.

Skeletal System 1. Lymphocytes are produced in red bone marrow.

Muscular System 1. Contraction of muscles compresses lymphatics and helps push the flow of lymph toward the right and left lymphatic ducts.

Nervous System 1. Undue stress may suppress the immune response. 2. The nervous system innervates large lymphatic vessels and helps regulate the immune response.

Endocrine System 1. The thymus gland confers immunologic competence on the T lymphocytes. 2. Hormones stimulate the production of lymphocytes.

Cardiovascular System 1. Blood plasma is the source of interstitial fluid, which becomes lymph when drained by lymph capillaries. 2. The lymphatic system returns this fluid to the bloodstream via the right and left subclavian veins, connecting with the right and left lymphatic ducts.

Digestive System 1. Lacteals in the villi of the small intestine absorb fats. 2. The hydrochloric acid in the gastric juice destroys most pathogens. 3. The digestive system digests and absorbs nutrients for lymphatic tissues. 4. Peyer’s patches in the wall of the small intestine destroy bacteria.

Respiratory System 1. The tonsils are located in the pharynx. 2. Breathing and contraction of the respiratory muscles maintain lymph flow through lymphatics. 3. Immune system cells receive their oxygen and get rid of carbon dioxide waste via the respiratory system.

Urinary System 1. The kidneys maintain homeostasis by regulating the amounts of extracellular fluid. 2. Electrolyte and acid-base levels of the blood are maintained by the urinary system for lymphoid tissue function. 3. Urine can flush out certain microorganisms from the body.

Reproductive System 1. The acid environment of the female vagina and male urethra prevent bacterial growth. 2. In the female reproductive tract, the immune system does not attack the male sperm as a foreign antigen, ensuring the possibility of fertilization.
CHAPTER 16
The function of the digestive system is to break down food (complex carbohydrates, proteins and fats) via hydrolysis into simpler substances or molecules that can be used by the body’s cells. This process is called digestion. Digestion allows the body’s cells to convert food energy into the high-energy adenosine triphosphate (ATP) molecules that run the cell’s machinery. The major organs and accessory structures that perform this function are collectively referred to as the digestive system.
The digestive system prepares food for use by cells through five basic activities: 1. Ingestion or the taking of food into the body 2. Peristalsis or the physical movement or pushing of food along the digestive tract 3. Digestion or the breakdown of food by both mechanical and chemical mechanisms 4. Absorption or the passage of digested food from the digestive tract into the cardiovascular and lymphatic systems for distribution to the body’s cells 5. Defecation or the elimination from the body of those substances that are indigestible and cannot be absorbed.
The organs of digestion are part of two main groups: 1. Gastrointestinal or alimentary tract 2. Accessory Structures
The first is the gastrointestinal tract, or alimentary canal, which is a long continuous tube that runs through the ventral cavity of the body and extends from the mouth to the anus. The length of this tube is approximately 30 feet, or 9 meters. Its organs include the mouth or oral cavity, pharynx, esophagus, stomach and the small and large intestine. Muscular contractions in the tube break down food physically by churning it; enzymes from cells in the tube’s wall break down food chemically.
The second group of organs consists of accessory structures. They include the teeth, tongue, salivary glands, liver and gallbladder and pancreas.
Breaking down food into simpler substances that the cells can use is the process of digestion
Hepatitis can be caused by hepatitis virus A or B.
Gallstones are caused by cholesterol.
A chronic, inflammatory bowel disease with unknown origin is Crohn’s disease.
Diverticulosis is a disorder characterized by herniation in the muscular layer of the colon.
Inflammation and enlargement of rectal veins is hemorrhoids (or piles).
Defecation is the elimination from the body of those substances that are indigestible and cannot be absorbed.
Taking of food into the body is known as ingestion.

The walls of the alimentary canal from the esophagus to the anal canal have the same arrangement of tissue layers. These layers are referred to as coats or tunics. There are four tunics of the canal. From the inside out they are called: the tunica mucosa (TYOO-nih-kah myoo-KOH-sah), the tunica submucosa, the tunica muscularis and the adventitia (ad-vin-TISH-ee-ah), or tunica serosa (see-ROH-sah).
The tunica mucosa is the innermost lining of the canal and consists of a mucous membrane attached to a thin layer of visceral muscle. Three layers make up the mucous membrane.
The first is an epithelial layer, which is in direct contact with the contents of the canal; the second is an underlying layer of loose connective tissue called the lamina propria (LAM-ih-nah PROH-pee-ah); and the third is the muscularis mucosa. The epithelial layer functions in protection, secretion of enzymes and mucus and absorption of nutrients. The lamina propria supports the epithelium, binds it to the muscularis mucosa and provides it with its lymph and blood supply. The tunica mucosa of the small intestine has another special layer, the muscularis mucosa, made of muscle fibers that produce folds to tremendously increase the digestive and absorptive area of the small intestine.
The tunica submucosa consists of loose connective tissue that binds the tunica mucosa to the next layer, the tunica muscularis.
The tunica muscularis of the mouth, pharynx and the first part of the esophagus consists of skeletal muscle that allows the voluntary act of swallowing. The rest of the tract consists of smooth muscle: an inner circular layer and an outer longitudinal layer of fibers. Involuntary contractions of these smooth muscle fibers break down food physically, mix it with the digestive secretions that break down food chemically and propel the food through the canal. The tunica muscularis also contains the major nerve supply to the alimentary canal, the plexus of Auerbach.
The tunica serosa is the outermost layer. It consists of serous membrane made up of connective and epithelial tissue. It is also known as the visceral peritoneum (VISS-er-al pair-ih-TOH-nee-um). This layer covers organs and has large folds that weave in and between the organs, thus binding the organs to each other and to the walls of the cavity. This layer also contains blood vessels, lymph vessels and nerves that supply the organs. One extension of the visceral peritoneum forms the mesentery (MEZ-in-tehr-ee).
The lining of the entire alimentary canal has four coats or tunics.
The tunica muscularis is responsible for propelling food along by peristalsis.
The mesentery is an extension of the visceral peritoneum.

The mouth or oral cavity can also be called the buccal (BUCK-ull) cavity. Its sides are formed by the cheeks. The roof consists of the hard and soft palates, and its floor is formed by the tongue. The lips are fleshy folds that surround the opening or orifice of the mouth. On the outside the oral cavity is covered by skin and on the inside by mucous membrane.
During the chewing of food, the lips and cheeks help keep food between the upper and lower teeth. They also assist in speech. The hard (bony) palate forms the anterior part of the roof of the mouth. The soft (muscular) palate forms the posterior portion of the roof of the mouth. Hanging from its posterior border is a cone-shaped muscular structure called the uvula (YOO-vyoo-lah), which functions in the swallowing process and prevents food from backing up into the nasal area.
The tongue and its associated muscles form the floor of the oral cavity. It consists of skeletal muscle covered with mucous membrane. It is divided into symmetrical halves by a septum called the lingual frenulum (LING-gwall FRIN-yoo-lum). The tongue is attached to and supported by the hyoid bone. There are two types of skeletal muscle found in the tongue: extrinsic and intrinsic. Extrinsic muscles originate outside the tongue and insert into it, moving the tongue from side to side and in and out to manipulate food. Intrinsic muscles originate and insert within the tongue, altering the size and shape of the tongue for speech and swallowing.

The upper surface and sides of the tongue are covered with papillae (pah-PILL-ay), which are projections of the lamina propria covered with epithelium. They produce the rough surface of the tongue. The anterior two-thirds contain taste buds and are most numerous at the tip of the tongue and on the posterior surface of the tongue. The filiform (FILL-ih-form) papillae, found at the front of the tongue, are rough and are important in licking. The fungiform (FUN-jih-form) papillae and the circumvallate (sir-kum-VAL-ate) papillae, found toward the back of the tongue, all contain taste buds. There are five tastes: sweet, sour, salt, umami and bitter.

The major portion of saliva is secreted by the large salivary glands. The mucous membrane lining of the mouth contains many small glands, called the buccal (BUCK-ull) glands, which secrete small amounts of saliva. The large salivary glands are found outside of the oral cavity and pour their secretions into ducts that empty into the mouth. The three pairs of salivary glands are the parotid (pah-ROT-id) gland, the submandibular (sub-man-DIB-yoo-lar) or submaxillary (sub-MACK-sih-lair-ee) gland and the sublingual (sub-LING-gwall) gland.
Saliva is 99.5% water, which provides a medium for dissolving foods. The remaining 0.5% consists of solutes: 1. Chlorides activate the salivary enzyme amylase (AM-ih-lays). 2. Amylase initiates the breakdown of complex carbohydrates like starch and glycogen into simple sugars. 3. Bicarbonates and phosphates, which are buffer chemicals, keep the saliva at a slightly acidic pH of 6.35 to 6.85. 4. Urea and uric acid are waste products. 5. Mucin forms mucus to lubricate food. 6. The enzyme lysozyme destroys bacteria, thus protecting the mucous membrane from infection and the teeth from possible decay.
The teeth, also known as the dentes (DEN-teez), are located in the sockets of the alveolar processes of the mandible and maxillae bones. The teeth break up food by chewing. Chewing is called mastication (mass-tih-KAY-shun). There are 20 temporary or deciduous teeth that form in infants between the ages of 6 months to 2 years. By the age of 13, there will develop 32 permanent teeth to replace the deciduous ones . The eight front teeth are called incisors (in-SIGH-zors) and are used to cut food. The four canine teeth are used to tear food. Because they have one cusp, they are also called cuspids (KUSS-pids). The molar teeth grind food. There are two kinds of molar teeth. The eight premolars have two cusps or projections and are also called bicuspids; the 12 molars have three cusps and are called tricuspids.

The alveolar processes are covered by the gums or gingivae (JIN-jih-vee) that extend slightly into each socket. The sockets are lined by the periodontal ligament that anchors the teeth in position and acts as a shock absorber to soften the forces created during chewing.
A tooth can be divided into three principal portions: 1. The crown is the portion above the level of the gums and is covered with enamel, the hardest substance in the body that protects the tooth from wear and acids. 2. The cervix or neck is the constricted junction between the crown and the root. 3. The root can consist of one, two or three projections embedded in the socket. Larger teeth, like molars, will have more than one root.
Teeth are made of dentin, a bonelike substance that encloses the pulp cavity in the crown. The exposed surface of the crown is covered with enamel. Narrow extensions of the pulp cavity project into the root, called root canals. At the base of each root canal is an opening, the apical foramen, through which blood vessels and nerves enter the tooth and become part of the pulp. The dentin of the root is covered with another substance called cementum, which attaches the root to the periodontal ligament.
The anterior part of the roof of the mouth is the hard palate.
The lingual frenulum is a septum dividing the tongue into symmetrical halves.
The tongue is supported by the hyoid bone.
Saliva is mostly water, but an important chemical activator in it is chloride.
The gingivae extend slightly into each tooth socket.
Infants’ teeth are called temporary or deciduous teeth.
Teeth can have as many as three root projections.
The term for chewing is mastication.
The dentin of a tooth is covered by enamel, the hardest substance in the body.
The enzyme that initiates the breakdown of complex carbohydrates like starch and glycogen into simple sugars is amylase.
The portion of the tooth above the level of the gums, which is covered with enamel, is the crown
Andrew and Sidney are trying to make each other laugh while drinking milk. In the middle of swallowing, Sidney suddenly bursts out laughing—and sprays milk through his nose. What structure normally prevents the flow of liquid and food into the nasal cavity when you swallow? The uvula normally keeps liquid and food from flowing into the nasal cavity when you swallow.
The pharynx (FAIR-inks) is part of both the digestive and the respiratory systems. Its function in the digestive system is to begin the process of swallowing or deglutition (deg-loo-TISH-un).
Swallowing moves food from the mouth to the stomach. Swallowing begins when the tongue, with the teeth and saliva, forms a soft mass called the food bolus. Food is forced to the back of the mouth cavity and into the oropharynx (or-oh-FAIR-inks). This is the voluntary stage of swallowing.
Next, the involuntary stage begins. First, the respiratory passageways close and breathing is temporarily interrupted. The food bolus stimulates oropharyngeal receptors that send impulses to the brain. This causes the soft palate and the uvula to move upward and close off the nasopharynx (nay-zoh-FAIR-inks). Now the larynx is pulled forward and upward under the tongue where it meets the epiglottis and seals off the glottis (the common opening into the trachea). The food bolus passes through the laryngopharynx and enters the esophagus in about 1 second. The respiratory passageways reopen and breathing resumes.
The esophagus (eh-SOFF-ah-gus) is a collapsible, muscular tube that is situated behind the trachea or windpipe. It is about 10 inches (23–25 cm) long and begins at the end of the laryngopharynx. It passes through the mediastinum (mee-dee-ass-TYE-num) (the space between the lungs), pierces the diaphragm (DYE-ah-fram) through an opening called the esophageal hiatus and ends at the superior portion of the stomach.
The function of the esophagus is to secrete mucus and transport food to the stomach. It does not produce any digestive enzymes and it does not absorb food. Food is pushed through the esophagus by smooth muscle contractions, called peristalsis, repeated in wavelike motions that push the food toward the stomach. Movement of solid or semisolid foods from the mouth to the stomach takes 4 to 8 seconds; liquids pass in about 1 second. Just above the diaphragm muscle, the esophagus is slightly narrowed by the lower esophageal or gastroesophageal sphincter (gas-troh-eh-soff-ah-JEE-al SFINGK-ter). This sphincter connects the esophagus with the stomach and controls the passage of food into the stomach.
There are three parts to the pharynx; they are the oropharynx, the laryngopharynx and the nasopharynx.
The tube connecting the laryngopharynx and the stomach is the esophagus, which passes through the diaphragm and mediastinum.
A soft mass of chewed food ready to be swallowed is known as a food bolus
The stomach is an enlargement of the gastrointestinal tract. It lies in the upper part of the abdominal cavity just under the diaphragm muscle. It has the shape of the letter J. When it is empty, it is about the size of a large sausage. However, it can be stretched to accommodate large amounts of food.
The stomach is divided into four parts: 1. the cardia surrounds the gastroesophageal sphincter; 2. the fundus is the rounded portion above and to the left of the cardia; 3. below the fundus is the large central portion of the stomach known as the body; and 4. the pylorus or antrum is the narrow inferior region that connects with the duodenum of the small intestine via the pyloric sphincter.
When there is no food in the stomach, the mucosa lies in large folds called rugae (ROO-ghee), which are visible with the unaided eye. As the stomach fills, the rugae smooth out and disappear, like an accordion when it is extended with air.
The mucosa of the stomach contains many pits or gastric glands that have three kinds of secreting cells: (1) the zymogenic (zye-moh-JEN-ik) or chief cells secrete the principal gastric enzyme pepsinogen (pep-SIN-oh-gen); (2) the parietal (pah-RYE-eh-tal) cells secrete hydrochloric acid, which activates the pepsinogen to become pepsin, the enzyme that begins to break down proteins; and (3) the mucous cells, which secrete mucus. The secretions of these gastric glands collectively are referred to as gastric juice.
The muscularis coat of the stomach has uniquely three, not just two, layers of smooth muscle: an inner oblique, a middle circular and an outer longitudinal. These three layers allow the stomach to contract in a variety of ways to break up food into small pieces, churn it and mix it with the gastric juice. When the stomach is empty and this activity occurs, we experience the stomach growling.

The main chemical activity of the stomach is to begin the digestion of proteins by the enzyme pepsin. The protein components of the stomach cells themselves are protected from being digested by the mucus secreted by the mucous cells.
The stomach then empties all its contents into the duodenum (doo-oh-DEE-num) of the small intestine approximately 2 to 6 hours after ingestion. Foods high in carbohydrates pass through the stomach first because their digestion begins in the mouth via the salivary enzyme amylase. Protein foods pass through somewhat more slowly because their digestion begins in the stomach. Foods containing large amounts of fats take the longest to pass into the duodenum. The stomach participates in the absorption of some water and salts. Certain drugs, such as aspirin and alcohol, can also be absorbed in the stomach.

The next step is chemical digestion in the small intestine. This process depends on secretions from intestinal glands and on secretions of the two large accessory glands of the system, the pancreas and the liver and its gallbladder.
The pancreas is a soft, oblong gland about 6 inches long and 1 inch thick. It is found beneath the great curvature of the stomach and is connected by a duct to the duodenum of the small intestine.
The pancreas is divided into a head (the part closest to the duodenum), the body (the main part) and the tail. Internally, the pancreas is made up of clusters of glandular epithelial cells. One group of these clusters, the islets of Langerhans, or the pancreatic islets, form the endocrine portions of the gland and are therefore part of the endocrine system. Some of these clusters consist of alpha cells that secrete the hormone glucagon (GLOO-kah-gon). Other clusters consist of beta cells that secrete the hormone insulin. (Review Chapter 12.) The other masses of cells are called the acini (AS-in-eye), which are the exocrine glands of the organ.
The acini release a mixture of digestive enzymes (lipases, carbohydrases and proteases) called the pancreatic juice, which leaves the pancreas through a large main tube called the pancreatic duct, or duct of Wirsung. The duct cells secrete sodium bicarbonate. In most individuals the pancreatic duct unites with the common bile duct of the liver and enters the duodenum in a common duct, originally called the ampulla (am-PULL-lah) of Vater but now is called the hepatopancreatic ampulla.
The functions of the pancreas are, therefore, twofold. The acini secrete enzymes that continue the digestion of food in the small intestine, and the alpha and beta cells secrete the hormones glucagon and insulin which regulate and control blood sugar levels.
The liver is one of the largest organs of the digestive system. The liver weighs approximately 4 pounds and is divided into two principal lobes: the right lobe and the left lobe, each separated from one another by the falciform ligament. The lobes of the liver are made up of numerous functional units called lobules.
The functions of the liver are so numerous and important that we cannot survive without it. The liver has six major functions: 1. Manufactures anticoagulant 2. Eat bacteria and old blood cells 3. Breakdown poisons 4. Collects newly absorbed excess nutrients 5. Store certain elements 6. Produce bile salt
The liver manufactures the anticoagulant heparin and most of the other plasma proteins, such as prothrombin and thrombin, that are involved in the blood clotting mechanism.
Kupffer cells of the liver phagocytose (eat) certain bacteria and old, worn-out white and red blood cells.
Liver cells contain various enzymes that either break down poisons or transform them into less harmful substances. If the body cannot break down and excrete certain poisons, it stores those poisons. When we digest proteins into amino acids, the amino acids go to the mitochondria to be converted into ATP. This process produces ammonia as a waste product, which is toxic to cells. The liver cells convert ammonia to urea (harmless) that is then excreted by the kidneys or the sweat glands.
Excessive newly absorbed nutrients are collected in the liver. Excess glucose and other monosaccharides can be stored as glycogen (animal starch) or converted to fat. When needed, the liver can then transform glycogen and fat into glucose.
The liver stores glycogen, copper and iron, as well as vitamins A, D, E and K.
The liver produces bile salts that break down fats. These bile salts are sent to the duodenum of the small intestine for the emulsification (breakup) and absorption of fats.

The gallbladder is a pear-shaped sac about 3 to 4 inches long located in a depression of the surface of the liver. Its lining, like the stomach, has rugae that allow it to expand and fill with stored bile. The gallbladder’s function is to store and concentrate the bile produced by the liver lobules until it is needed in the small intestine. The bile enters the duodenum through the common bile duct.
The stomach begins with the cardia and ends at the pylorus (or antrum).
Alpha and beta cells of the pancreas secrete, respectively, glucagon and insulin.
Acini, the exocrine glands of the pancreas, secrete pancreatic juices.
The pear-shaped sac about 3 to 4 inches long that stores and concentrates bile until it is needed in the small intestine is the gallbladder
The rounded upper portion of the stomach that is above and to the left of the cardia is known as the fundus
Gallstones are a solidification of bile in the gallbladder, usually due to excess cholesterol. Some are painless, while others may cause intense pain as they pass through ducts connecting the gallbladder and small intestines. Trace the path of a gallstone from the gallbladder to where it would exit the body. Gallbladder to cystic duct to common bile duct to Ampulla of Vater (hepatopancreatic ampulla) to duodenum to je junum to ileum to cecum to ascending colon to transverse colon to descending colon to sigmoid colon to rectum to anus

The major portion of absorption and digestion occurs in the small intestine. It is approximately 21 feet in length and averages 1 inch in diameter. The small intestine is divided into three portions. First is the duodenum, which is the shortest part, and is about 10 inches long. The duodenum originates at the pyloric sphincter and joins the second portion, the jejunum (jee-JOO-num). The jejunum is about 8 feet long and extends to the third part, the ileum (ILL-ee-um), which measures 12 feet and joins the large intestine at the ileocecal (ill-ee-oh-SEE-kal) valve (sphincter).
The mucosa of the small intestine contains many pits lined with glandular epithelium. These pits are known as the intestinal glands or crypts of Lieberkuhn (KRIPTZ of LEE-ber-koon). They secrete the intestinal digestive enzymes that supplement the bulk of the digestive enzymes secreted by the liver and the pancreas. The submucosa of the duodenum contains numerous Brunner’s glands, now called duodenal glands, which secrete an alkaline mucus. Additional mucus is secreted by goblet cells. This mucus protects the walls of the small intestine from being digested by enzymes and neutralizes the acid found in the chyme(KIGHM). Chyme is the term used to describe the digested, viscous, semifluid contents of the intestine.
Approximately 80% of all absorption of nutrients (simple sugars, amino acids, fatty acids, water, vitamins and minerals) occurs in the small intestine. The anatomic structure of the small intestine is highly specialized for this function. First of all, the tract is 21 feet long. Second, an even larger surface for absorption of nutrients is provided by the structure of the walls of the tract, which are thrown into a series of folds called plicae (PLYE-kee). Third, the mucosal coat is transformed into projections called villi, which look like microscopic eye dropper bulbs approximately 0.5 to 1 mm long.
A tremendous number of villi line the intestine, about 4 to 5 million. These villi vastly increase the surface area of the epithelium for absorption of nutrients. The structure of each villus contains a capillary network where blood picks up nutrients, a venule or small vein to transport the nutrients, an arteriole or small artery and a lacteal of the lymphatic system to pick up fats.
In addition, the individual epithelial cells that cover the surface of a villus have a brush border of microvilli to further increase the absorptive capability of the small intestine. Nutrients that pass through the epithelial cells covering the villus are able to pass through the endothelial cells of the capillary walls and through the lacteals to enter the blood and lymphatic circulatory systems. From there they are transported to the trillions of cells in the body.

The functions of the large intestine are the absorption of water, the manufacturing and absorption of certain vitamins and the formation and expulsion of the feces (FEE-seez). The large intestine is about 5 feet in length and averages 2.5 inches in diameter. It is also referred to as the bowel. It is attached to the posterior wall of the abdomen by extensions of its visceral peritoneum known as the mesocolon. It is divided into four principal regions: (1) the cecum (SEE-kum), the pouchlike first part of the large intestine; (2) the colon (KOH-lon), the largest part; (3) the rectum; and (4) the anal canal.

The opening from the ileum of the small intestine into the cecum of the large intestine is a fold of mucous membrane known as the ileocecal valve. This valve allows material to pass from the small intestine into the large intestine. The cecum, a blind pouch (one end is closed), is 2 to 3 inches long and hangs below the ileocecal valve. Attached to the closed end of the cecum is the twisted tube known as the vermiform (VER-mih-form) appendix, about 3 inches in length. The open end of the cecum merges with the long tube called the colon.
The colon looks like a tube of consecutive pouches. The pouches are called haustrae (HAW-stree). The first part of the colon is known as the ascending colon. It rises on the right side of the abdomen, reaches the undersurface of the liver and turns to the left at the right colic (hepatic) flexure. The right colic flexure continues across the abdomen to the left side as the transverse colon. It then curves beneath the lower end of the spleen to the left side as the left colic (splenic) flexure. Next it passes downward as the descending colon. The last part of the colon is called the sigmoid (SIG-moyd) colon, where the colon joins the rectum.

Three mechanical movements occur in the large intestine: 1. Haustral churning 2. Peristalsis at the rate of 3 to 12 contractions per minute 3. Mass peristalsis

The rectum is the last 7–8 inches of the gastrointestinal tract. It is situated anterior to the sacrum and the coccyx. (Review Chapter 7.) The terminal 1 inch of the rectum is called the anal canal. The mucous membrane of the anal canal is arranged in a series of longitudinal folds called the anal columns that contain a network of arteries and veins.
The opening of the anal canal to the exterior is called the anus. It is guarded by an internal sphincter of smooth muscle and an external sphincter of skeletal muscle.

The absorption of water is an important function of the large intestine. In addition, bacteria in the colon manufacture three important vitamins that are also absorbed in the colon: vitamin K needed for clotting, biotin needed for glucose metabolism and vitamin B5 needed to make certain hormones and neurotransmitters. Mucus is also produced by glands in the intestine. Intestinal water absorption is greatest in the cecum and ascending colon.

By the time the chyme has remained in the large intestine 3–10 hours, it is a semisolid mass of material as a result of the absorption of water and is now known as the feces. The feces consist of water, inorganic salts and epithelial cells from the mucosa of the tract that were scraped away as the chyme moved through the tract.

In addition the feces have bacteria, in particular Escherichia coli, a normal inhabitant of our intestine that feeds on undigested materials. The products of bacterial decomposition, such as gas and odor (hydrogen sulfide gas, H2S, which produces a “rotten egg” odor), and undigested parts of food not attacked by bacteria are also found in the feces. The more fiber (the cellulose of plant cell walls from eating fruits and vegetables) in the diet, the more undigestible materials in the feces and the softer the stool.
When mass peristalsis pushes the fecal material into the rectum, it causes distention of the rectal walls. This triggers pressure-sensitive receptors in the walls of the rectum, sending an impulse to the nervous system, which initiates the reflex for defecation. Defecation is the act of emptying the rectum and is the final activity of the digestive system.

The small intestine begins with the duodenum and ends with the ileum.
The walls of the small intestine are protected from digestion by mucus.
The folds of the mucosa of the small intestine are called plicae and the projections are called villi.
The bowel begins with the cecum and ends at the anal canal.
The final act of the digestive system is defecation.
Approximately 80% of all absorption of nutrients (simple sugars, amino acids, fatty acids, water, vitamins, and minerals) occurs in the small intestine
The folds of the mucosa of the small intestine which increase the surface area for absorption of nutrients are called plicae The digested, viscous, semifluid contents of the small intestine are known as chime
“Oh, my stomach hurts!” complains Bridget, as she holds her lower abdomen. Her sister says “That’s not your stomach; that’s your large intestine.”
Integumentary System 1. The skin protects the organs of the system and provides vitamin D needed for calcium absorption in the intestine. 2. The digestive system provides nutrients for growth and repair of the integument. 3. Fat for insulation is deposited beneath the skin in the subcutaneous tissue.

Skeletal System 1. The bones protect some digestive organs and the hyoid bone provides support for the tongue. 2. Yellow bone marrow stores fat. 3. The digestive system supplies calcium and nutrients for bone growth and repair.

Muscular System 1. Smooth muscle pushes food and nutrients along the digestive tract via peristalsis. 2. Skeletal muscles protect and support the abdominal organs. 3. The digestive system provides nutrients such as glucose for muscle contraction, growth and repair. 4. The liver metabolizes lactic acid after anaerobic muscle contraction.

Nervous System 1. The nervous system sends impulses for muscular contractions in the walls of the gastrointestinal tract for peristalsis to occur. 2. Nerve impulses coordinate swallowing and defecation. 3. The digestive system provides nutrients for the growth, maintenance and functioning of neurons and neuroglia cells.

Endocrine System 1. Hormones help regulate the metabolism of nutrients for growth and development. 2. Insulin and glucagon control sugar metabolism. 3. The digestive system provides nutrients to maintain the endocrine glands.

Cardiovascular System 1. The cardiovascular system distributes, via the blood, nutrients absorbed in the small intestine to all tissues of the body. 2. The digestive system provides the nutrients for maintaining the organs of the circulatory system and absorbs iron for hemoglobin production and water for blood plasma formation.

Lymphatic System 1. The lacteals of the villi of the small intestine absorb fats and transport them to the blood. 2. Lymphoid tissues protect the digestive organs from infection. 3. The digestive system provides nutrients for the lymphoid organs for growth and repair. 4. The hydrochloric acid of the stomach destroys most pathogens that may enter the body with food.

Respiratory System 1. The respiratory system provides the cells of the digestive tract with oxygen needed for metabolism and takes away the waste product carbon dioxide. 2. Breathing can occur through the mouth due to the pharynx, which is shared by both systems. 3. The digestive system provides nutrients for the respiratory organs.

Urinary System 1. The kidneys convert vitamin D to a form needed for calcium absorption and reabsorb water lost in the digestive tract. 2. The digestive system provides nutrients to the organs of the urinary system. 3. The liver converts harmful ammonia from the digestion of proteins to harmless urea and provides bile to emulsify fats.

Reproductive System 1. When a woman is pregnant, the fetus crowds the abdominal organs and the mother may experience constipation. 2. The digestive system provides nutrients for maintenance, growth and repair of the reproductive organs and supplies the developing fetus with nutrients.
CHAPTER 17

The trillions of cells of our body need a continuous supply of oxygen to carry out the various and vital processes that are necessary for their survival. Cellular respiration, which converts food into the chemical energy of adenosine triphosphate (ATP), produces large quantities of carbon dioxide. An excess accumulation of this gas in tissue fluids produces acidic conditions that can be poisonous to cells. Thus, this gas must be quickly eliminated.
The two systems of the body that share the responsibility of supplying oxygen and eliminating carbon dioxide are the cardiovascular system and the respiratory system. The respiratory system consists of the organs that exchange these gases between the atmosphere and the blood. Those organs are the nose, pharynx, larynx, trachea, bronchi and lungs. In turn, the blood in the cardiovascular system transports these gases between the lungs and the cells.
The overall exchange of gases between the atmosphere, the blood and the cells is called respiration. This term is to be distinguished from the biochemical meaning of respiration discussed in Chapter 4. The respiratory and cardiovascular systems participate equally in respiration. If either system malfunctions, the body cells will die from oxygen deprivation and accumulation of carbon dioxide and death will be inevitable.
There are two systems responsible for supplying oxygen and eliminating carbon dioxide; they are the respiratory and the cardiovascular systems.
Cystic fibrosis affects the secretory cells of the lungs.
Any infection in the lungs is known as pneumonia.
Whooping cough is also known as pertussis
The disease caused by excessive exposure to asbestos, silica or coal dust is pulmonary fibrosis
Bronchitis causes a swelling of the mucous membrane
The respiratory and cardiovascular systems play an equal part in the overall exchange of gases between the atmosphere, the blood, and the cells, which is known as respiration

The nose has an external part and an internal part that is inside the skull. Externally, the nose is formed by a framework of cartilage and bone covered with skin and lined internally with mucous membrane. The bridge of the nose is formed by the nasal bones that help support the external nose and hold it in a fixed position. On the undersurface of the external nose are two openings called the nostrils or external nares (ex-TER-nal NAIRZ). The hard palate of the mouth forms the floor of the nasal cavity, separating the nasal cavity from the oral cavity.
Anteriorly, the internal nose merges with the external nose. Posteriorly, it connects with the pharynx (FAIR-inks) or throat via two openings called the internal nares. The nasolacrimal ducts from the lacrimal or tear sacs empty into the nose, as well as four paranasal sinuses (air-filled spaces inside bone): 1. Sphenoidal 2. Frontal 3. ethmoidal 4. maxillary
The inside of both the internal and external nose is divided into right and left nasal cavities by a vertical partition known as the nasal septum. This septum is made primarily of cartilage. The top of the septum is formed by the perpendicular plate of the ethmoid bone and the lowermost portion is formed by the vomer bone. (Review Chapter 7.) The anterior portions of the nasal cavities just inside the nostrils are known as the vestibules (VESS-tih-byoolz).
These interior structures of the nose have three specialized functions: 1. First, air is warmed, moistened and filtered as it enters the nose. 2. Second, olfactory (olh-FAK-toh-ree) stimuli are detected for the sense of smell. 3. Third, large hollow resonating chambers are present for creating speech sounds.
As the incoming air enters the nostril, it first passes through the vestibule. Because the vestibule is lined with coarse hairs, it filters out large dust particles. This is the body’s first line of defense to prevent foreign objects from entering the respiratory system. The air then moves into the rest of the cavity.
Three shelves are formed by the projections of the superior, middle and inferior conchae or turbinate bones. These extend out from the lateral wall of the cavity and almost reach the nasal septum. The cavity is subdivided into a series of narrow passageways called the superior meatus (soo-PEER-ih-or mee-AY-tus), middle meatus and inferior meatus. Mucous membranes line the cavity and those shelves.

Olfactory receptors are located in the membrane that lines the superior meatus; this area is called the olfactory region. Below, the membrane consists of pseudostratified, ciliated columnar epithelial cells with many goblet cells that produce mucus. Blood capillaries are also found here. As the air whirls around the turbinate bones and meati, or shelf passageways, it is warmed by the capillaries. Mucus secreted by the goblet cells moistens the air and traps particles not filtered by the hairs in the nose.

In addition, drainage from the lacrimal ducts and sinuses help moisten the air. The cilia on the free edge of the epithelial cells move this mucus-dust package back toward the throat so it can be swallowed and eliminated from the body through the digestive system. Its enzymes and acidic environment will destroy most microorganisms that may have entered with the air.
The bridge of the nose is formed by the nasal bones.
The underside of the external nose has two openings called nostrils.
Posteriorly, the internal nose connects with the pharynx.
The nasal septum divides the left and right nasal cavities
Olfactory receptors are located in the membrane of the superior meatus.
The vertical partition that divides the nose into right and left nasal cavities is the nasal septum
The pharynx is also called the throat. It is a tube approximately 5 inches (13 cm) long that begins at the internal nares and extends part way down the neck. Its position in the body is noted just posterior to the nasal and oral cavities and just anterior to the cervical vertebrae. Its walls are made of skeletal muscle lined with mucous membrane. The pharynx is a passageway for both air and food and forms a resonating chamber for speech sounds. It is divided into three portions.

The uppermost portion is called the nasopharynx (nay-zoh-FAIR-inks). It has four openings in its walls: the two internal nares and, just behind those, the two openings that lead into the auditory or eustachian (you-STAY-shen) tubes. In its posterior wall the pharyngeal or adenoid tonsils are located.
The second portion is called the oropharynx (or-oh-FAIR-inks). It has only one opening, the fauces (FOH-sez), which connects with the mouth. Hence, the oropharynx is a common passageway for both food and air. The palatine and lingual tonsils are found in the oropharynx.
The lowermost portion is called the laryngopharynx (lah-ring-go-FAIR-inks). It connects with the esophagus posteriorly and with the larynx anteriorly. The pharynx or throat serves as both a connection between the mouth and the digestive tract and as a connection between the nose and the respiratory system.
The larynx (LAIR-inks) is also called the voice box. It is a very short passageway that connects the pharynx with the trachea. Its walls are supported by nine pieces of cartilage. Three of the pieces are single and three are paired. The three single pieces are the thyroid (THIGH-royd) cartilage, the epiglottis (ep-ih-GLOT-iss) and the cricoid (KRYE-koyd) cartilage.

The thyroid cartilage is the largest piece of cartilage and is also known as the Adam’s apple. It is larger in males than in females and can be easily seen externally, moving up and down when a person is speaking or swallowing. The epiglottis is a large, leaf-shaped piece of cartilage. It lies on the tip of the larynx. It can be viewed in its entirety from a posterior view, but, anteriorly, one can only see its tip. The stem part is attached to the thyroid cartilage, but the leaf part is unattached and is free to move up and down like a trap door.
When we swallow, this free edge or leaflike part pulls down and forms a lid over the glottis (GLOT-iss). The glottis is the space between the vocal cords in the larynx. The larynx is closed off when we swallow, so that foods and liquids get routed posteriorly into the esophagus and are kept out of the trachea anteriorly. If anything other than air passes into the larynx, a cough reflex should dislodge the foreign material.

When we try to talk and swallow at the same time, we choke and the cough reflex functions. Sensory receptors in the larynx detect the foreign substance and send a signal to the medulla oblongata, which triggers the cough reflex. Air is taken in and the vestibular folds and vocal cords tightly close trapping the air in the lungs. Muscular contractions increase the pressure in the lungs and the cords open, forcing air from the lungs at a very high velocity and carrying any foreign substance with it.
The cricoid cartilage is a ring of cartilage that forms the lowermost or inferior walls of the larynx. It attaches to the first ring of cartilage of the trachea. This is the last of the three unpaired cartilages. The six paired cartilages consist of three cartilages on either side of the posterior part of the larynx. The paired arytenoid (ahr-oh-TEE-noyd) cartilages are ladle-shaped and attach to the vocal cords and laryngeal muscles and by their action they move the vocal cords. The corniculate (kor-NIK-yoo-late) cartilages are cone-shaped; the paired cuneiform (kyoo-NEE-ih-form) cartilages are rod-shaped. The cuneiforms are located in the mucous membrane fold that connects the epiglottis to the arytenoid cartilages.

The mucous membrane of the larynx is arranged into two pairs of folds: an upper pair called the vestibular (vess-TIB-yoo-lar) folds or false vocal cords; and a lower pair called the vocal folds or true vocal cords.
When the vestibular folds come together, they prevent air from exiting the lungs as when you hold your breath. Along with the epiglottis, the vestibular folds can prevent food or liquids from getting into the larynx. Under the mucous membrane of the true vocal cords lie bands of elastic ligament, stretched between pieces of rigid cartilage like the strings of a guitar. Skeletal muscles of the larynx are attached internally to the pieces of rigid cartilage and to the vocal folds. When the muscles contract, the glottis or opening is narrowed.
As air exits the lungs and is directed against the vocal cords, they vibrate and set up sound waves in the column of air in the pharynx, nose and mouth. The greater the pressure of air, the louder the sound. Take a full breath of air in and force it out all at once. You will create a very loud sound. However, if you take in a full breath of air and let it out slowly with less pressure, the sound you create will be much softer sounding.
Pitch is controlled by tension on the true vocal cords. When the cords are pulled taut by the muscles, they vibrate more rapidly and a higher pitch results. Decreasing the muscular tension produces lower pitch sounds. Try it. Because the true vocal cords are usually thicker and longer in men than in women, they vibrate more slowly so men have a lower range of pitch than women.
Sound originates from the vibrations of the true vocal cords. In humans, this sound is converted into speech. The pharynx, mouth, nasal cavities and the paranasal sinuses all function as resonating chambers. The movement of the tongue and cheeks also contribute to creating the individual quality of human speech.
The adenoid tonsils are located in the posterior wall of the eustachian tube
The opening of the oropharynx is called the fauces
The epiglottis forms a lid over the glottis
The paired rod-shaped cartilage structures of the larynx are the cuneiform
The upper pair of folds of the mucous membrane of the larynx are called the vestibular folds or false vocal cords
Also known as the Adam's apple the thyroid cartilage is the largest piece of cartilage in the larynx.
The pharynx, or throat, is a passageway for both air and food and forms a resonating chamber for speech sounds.
The larynx, also called the voice box, is a very short passageway that connects the pharynx with the trachea.
The trachea (TRAY-kee-ah) is also referred to as the windpipe. It is a tubular passageway for air approximately 4.5 inches in length and about 1 inch in diameter. It is found anterior to the esophagus and extends from the cricoid cartilage of the larynx to the fifth thoracic vertebra, where it divides into the right and left primary bronchi.

The tracheal epithelium is pseudostratified, ciliated columnar cells with goblet cells and basal cells. The goblet cells produce mucus, and the ciliated cells provide the same protection against dust particles as does the membrane in the larynx and pharynx. The cilia beat upward and move the mucus-dust package to the throat for elimination from the body.

The smooth muscle and elastic connective tissue of the trachea are encircled by a series of 16 to 20 horizontal incomplete rings of hyaline cartilage that resemble a stack of Cs. The open part of the Cs face the esophagus and allow it to expand into the trachea during swallowing. When we swallow, we stop breathing to permit the large food bolus to expand into the trachea on its way to the stomach. The solid part of the Cs provides a strong rigid support for the tracheal walls so that they do not collapse inward and obstruct the air passageway. Varying pressure, as air moves in and out of the trachea, would collapse the tube if the cartilaginous rings were not present.
If a foreign object becomes caught in the trachea and cannot be expelled by the cough reflex, a tracheostomy may be necessary to save the person’s life. A tracheostomy is an incision into the trachea creating a new opening for air to enter. It is usually done between the second and third tracheal cartilages. This temporary opening can be closed, once the blocking object has been removed.
The trachea terminates in the chest by dividing into a right primary bronchus (RITE PRYE-mary BRONG-kus) that goes to the right lung and a left primary bronchus which goes to the left lung. The right primary bronchus is more vertical, shorter and wider than the left. Consequently, if a foreign object gets past the throat into the trachea, it will frequently get caught and lodge in the right primary bronchus. The bronchi, like the trachea, also contain the incomplete rings of hyaline cartilage and are lined with the same pseudostratified, ciliated columnar epithelium.
On entering the lungs, the primary bronchi divide to form smaller bronchi called the secondary or lobar bronchi, one for each lobe of the lung. The right lung has three lobes and the left lung has two lobes. The secondary bronchi continue to branch forming even smaller bronchi called tertiary or segmental bronchi. These branch into the segments of each lobe of the lung. Tertiary or segmental bronchi divide into smaller branches called bronchioles (BRONG-kee-olz). Bronchioles finally branch into even smaller tubes called terminal (end) bronchioles. This continuous branching of the trachea resembles a tree trunk with branches. For this reason this branching is commonly referred to as a bronchial tree.

As the branching becomes more and more extensive, the rings of cartilage get replaced with plates of cartilage. These finally disappear completely in the bronchioles. As the cartilage decreases, the amount of smooth muscle in the branches increases. In addition the pseudostratified, ciliated columnar epithelium changes to a simple, cuboidal epithelium.
The lungs are paired, cone-shaped organs located in and filling the pleural divisions of the thoracic cavity. Two layers of serous membrane, known as the pleural (PLOO-rah) membrane, enclose and protect each lung. The outer layer attaches the lung to the wall of the thoracic cavity and is called the parietal (pah-RYE-eh-tal) pleura. The inner layer is called the visceral (VISS-er-al) pleura and covers the lungs.
Between these two layers is a small space called the pleural cavity, which contains a lubricating fluid that is secreted by the membranes. This pleural fluid prevents friction between the two membranes and allows them to slide past each other during breathing, as the lungs and thorax change shape. It also assists in holding the pleural membranes together. Pleurisy (PLOOR-ih-see), or pleuritis, is an inflammation of this area and is very painful.
The right lung with its three lobes is thicker and broader than the left lung with its two lobes. The right lung is also a bit shorter than the left because the diaphragm muscle is higher on the right side, and it must make room for the liver that is found below it. The left lung is thinner, longer and narrower than the right.

The segment of lung tissue that each tertiary or segmental bronchi supplies is called a bronchopulmonary (brong-koh-PULL-mon-air-ree) segment. Each of these segments is divided into many small compartments called lobules (LOB-yoolz). Every lobule is wrapped in elastic connective tissue and contains a lymphatic vessel, an arteriole, a venule and bronchioles from a terminal bronchiole.

Terminal bronchioles subdivide into microscopic branches called respiratory bronchioles. These respiratory bronchioles further subdivide into 2 to 11 alveolar (al-VEE-oh-lar) ducts or atria. Around the circumference of the alveolar ducts are numerous alveoli (al-VEE-oh-lye) and alveolar sacs. An alveolus (singular) is a cup-shaped or grapelike out-pouching lined with epithelium and supported by a thin, elastic basement membrane. Alveolar sacs are two or more alveoli that share a common opening.

The actual exchange of the respiratory gases between the lungs and blood occurs by diffusion across the alveoli and the walls of the capillary network that surrounds the alveoli. This membrane, through which the respiratory gases move, is referred to as the alveolar capillary or respiratory membrane.

The surface of the respiratory membrane inside each alveolus is coated with a fluid, consisting of a mixture of lipoproteins called surfactant (sir-FAK-tant). This material is secreted by certain alveolar cells (alveolar type II cells). Surfactant helps reduce surface tension (the force of attraction between water molecules) of the fluid. Therefore, surfactant helps prevent the alveoli from collapsing or sticking shut as air moves in and out during breathing.
The gases need only diffuse through a single squamous epithelial cell of an alveolus and the single endothelial cell of the capillary to reach the red blood cell inside the capillary. It has been estimated that the lungs contain over 300 million alveoli. This is an immense surface area of 70 square meters (753 square feet) for the exchange of oxygen and carbon dioxide. This is about the square footage of a small house or cottage.

The principal purpose of respiration is to supply the trillions of cells of the body with oxygen and to remove the carbon dioxide produced by cellular activities. There are three basic processes of respiration.
The first process is ventilation or breathing, which is the movement of air between the atmosphere and the lungs. Ventilation has two phases: inhalation or inspiration to move air into the lungs and exhalation or expiration to move air out of the lungs.
The second and third processes of respiration involve the exchange of the gases within the body. External respiration is the exchange of gases between the lungs and the blood, the second process. The third process is called internal respiration, which is the exchange of gases between the blood and the body cells.
When the diaphragm and external intercostal muscles contract, we breathe in. This occurs because as the dome-shaped diaphragm contracts, it moves downward and flattens and the height of the thoracic cavity increases. Simultaneous contraction of the external intercostals lifts the rib cage and pushes the sternum forward. The lungs get stretched to the larger size of the thorax. Gases within the lungs spread out to fill the larger space, resulting in a decrease in gas pressure, causing a vacuum that sucks air into the lungs. This is inspiration.
As the diaphragm and external intercostals relax, the rib cage descends, the space decreases and the gases inside the lungs come closer together. Pressure increases, causing the gases to flow out of the lungs. This is expiration and we breathe out. This is mainly a passive activity. When we force air out, the internal intercostal muscles contract to help further decrease the size of the rib cage.

The pressure of a gas will determine the rate at which it diffuses from one area to another. Review the discussion of diffusion in Chapter 2. Molecules move from an area of high concentration to an area of low concentration. In a mixture of gases, like the air, each gas contributes a portion of the total pressure of the mixture.
The partial pressure of a gas is the amount of pressure that gas contributes to the total pressure and is directly proportional to the concentration of that gas in the mixture. Air is 78% nitrogen, 21% oxygen and 0.04% carbon dioxide, and the rest a mixture of other gases. Because air is 21% oxygen it makes up 21% of atmospheric pressure (21% of 760 mm Hg). We can abbreviate the partial pressure of oxygen as PO2 = 160 mm Hg and carbon dioxide as PCO2 = 0.3 mm Hg in air.

When a mixture of gases dissolves in blood, the resulting concentration of each gas is proportional to its partial pressure. Each gas diffuses between the blood and its surrounding tissues from areas of high partial pressure to areas of low partial pressure, until the partial pressure in the areas reaches equilibrium.
The PCO2 in capillary blood is 45 mm Hg. The PCO2 in alveolar air is 40 mm Hg. Because of these differences in partial pressures, carbon dioxide diffuses from blood, where its partial pressure is higher at 45 mm Hg, across the respiratory membrane into alveolar air, where its partial pressure is lower at 40 mm Hg. Similarly, the PO2 of capillary blood is 40 mm Hg, while that of alveolar air is 104 mm Hg. Therefore, oxygen diffuses from alveolar air, where the partial pressure is higher at 104 mm Hg, into the blood, where the partial pressure is lower at 40 mm Hg. The blood then leaves the lungs with a PO2 of 104 mm Hg.
The blood then transports oxygen to tissue cells and picks up carbon dioxide waste from the tissue cells. The tissue cells are high in carbon dioxide from cellular metabolic activities and low in oxygen, because it is used up in those activities. The pressure of CO2 is higher in tissue cells than in blood cells and diffuses from tissues to blood cells. The blood cell is higher in O2 levels than the tissue cells; thus, the pressure of O2 in blood is higher and diffuses into tissue cells, where it is lower. Recall that it is the iron atoms in heme that carry the oxygen and the protein globin that carries the carbon dioxide. The hemoglobin molecule in the red blood cell transports these gases.
The goblet cells of the trachea produce mucus
There are 16 to 20 incomplete rings of hyaline cartilage in the trachea.
The lobar bronchi are the secondary bronchi and the segmental bronchi are the tertiary bronchi.
The outer layer of the membrane covering the lungs is the parietal pleura and the inner layer is the visceral pleura.
The air sacs where gas exchange takes place are the alveoli.
A tracheostomy is an incision into the trachea, creating a new opening for air to enter.
The surface of the respiratory membrane inside each alveolus is coated with a fluid consisting of a mixture of lipoproteins called surfactant.
The first process of respiration is breathing or ventilation, which is the movement of air between the atmosphere and the lungs.
External respiration is the exchange of gases between the lungs and the blood, the second process of respiration.
The third process of respiration is called internal respiration, which is the exchange of gases between the blood and the body cells.
The partial pressure of a gas is the amount of pressure that gas contributes to the total pressure and is directly proportional to the concentration of that gas in the mixture.
The double-folded serous membrane that encloses and protects the lungs is the pleural membrane
The grape-like outpouchings of epithelium and elastic basement membrane surrounded by a capillary network, located at the end of the respiratory bronchioles, are the alveoli
The space between the two layers of the pleura, which contains a lubricating fluid that decreases friction between the membranes during the breathing process, is called the pleural cavity
Navarro is eating in a restaurant when he sees a man choking on the other side of the room. He races over and tries the Heimlich maneuver repeatedly with no success, and the man loses consciousness. The EMTs arrive within minutes and quickly pull out a kit to create a new airway for the man. What is the procedure called that they are about to perform? Where will the airway be created? The procedure is a tracehostomy. The airway will be created in the trachea just below the larynx.

Aaron is punched in the solar plexus, temporarily paralyzing his diaphragm. How will this affect his respiratory system? If you cannot contract the diaphragm, there will be very little size difference in the thoracic cavity. No change in size means no change in pressure, which means that air cannot flow into the body. In short, you cannot breathe.
When getting a physical for the soccer team, Brianna notices that the doctor keeps moving the stethoscope while listening to her breathing. What sections of the lungs is the doctor checking?
The doctor is listening to all the lobes of the lungs: three on the right, two on the left.
Integumentary System 1. The skin is the first line of defense because it forms a barrier to protect respiratory organs and tissues from microorganisms. 2. Stimulation of receptors in the skin can alter respiratory rates.

Skeletal System 1. Bones provide attachments for the muscles involved in breathing, for example, the intercostals. 2. The ribs and sternum enclose and protect the lungs and bronchi in the thoracic cavity.

Muscular System 1. The diaphragm and intercostal muscles produce changes in the volume of the thorax and lungs, resulting in the ability to inhale and exhale. 2. The respiratory system eliminates the carbon dioxide produced by contracting muscle cells.

Nervous System 1. The brainstem has control centers that regulate the respiratory rate. 2. The respiratory system supplies nerve cells with needed oxygen for maximum efficiency.

Endocrine System 1. Hormones stimulate red blood cell production, and the blood cells carry the oxygen and carbon dioxide for the respiratory system. 2. Epinephrine dilates bronchioles, increasing breathing abilities. 3. Testosterone causes the enlargement of the thyroid cartilage, producing the prominent Adam’s apple in men.

Cardiovascular System 1. The heart pumps the oxygen carrying red blood cells from the lungs through its system of arteries and veins to tissue cells where oxygen is exchanged with carbon dioxide.

Lymphatic System 1. The immune system protects respiratory organs from infection and cancers. 2. The tonsils in the pharynx produce immune cells.

Digestive System 1. The pharynx is used by both the digestive and the respiratory systems. 2. The digestive system provides nutrients to respiratory organs and tissues.

Urinary System 1. The kidneys and the respiratory system help maintain blood pH. 2. The kidneys reabsorb the water lost through breathing by filtering water from the blood.

Reproductive System 1. Breathing rates increase during sexual activities. 2. Fetal respiration occurs through the placenta with the mother.
CHAPTER 18
As the body metabolizes the various foods and nutrients taken in through the digestive tract, body cells produce metabolic wastes in the form of carbon dioxide, heat and water. The breakdown of proteins into amino acids and the subsequent metabolism of the amino acids produces nitrogenous wastes like ammonia. The harmful ammonia is converted by liver enzymes into less harmful urea. In addition, the body accumulates excess ions of sodium, chloride, potassium, hydrogen, sulfate and phosphate.
It is the role of the urinary system to maintain a balance of these products and to remove excesses from the blood. This system helps to keep the body in homeostasis by both removing and restoring selected amounts of solutes and water from the blood. See Concept Maps 18-1 and 18-2: The Urinary System. The urinary (YOO-rih-nair-ee) system consists of two kidneys, two ureters, the urinary bladder and the urethra.
The kidneys regulate the composition and volume of the blood and remove wastes from the blood in the form of urine. The urine consists of the metabolic waste urea, excess water, excess ions and toxic wastes that may have been consumed with food. Urine is excreted from each kidney through the kidney ureter. It is then stored in the urinary bladder, until it is expelled from the body through the urethra.
The kidneys are extremely efficient organs and are crucial in maintaining homeostasis in the body. A person can function very well with only one kidney, as we know from hearing about kidney donations among family members. In fact, as long as at least one-third of the kidney is functional, a person can survive. However, if kidney failure occurs, death is inevitable without medical treatment through kidney dialysis.
Other systems of the body also participate in waste excretion. The respiratory system excretes carbon dioxide and water vapor. The integumentary system excretes dissolved wastes (e.g., urea) in perspiration. The digestive system excretes indigestible materials, like plant fiber, and some bacteria.
Gout is a condition caused by high concentrations of uric acid in the plasma. This condition was once believed to be caused by excess food intake, but it may be inherited. The crystals of uric acid get deposited in joints of the hands and feet, causing inflammation and great pain. Gout is treated with drugs that inhibit uric acid reabsorption. Uric acid forms from the metabolism of certain nitrogen bases in nucleic acids.
Cystitis is an inflammation of the urinary bladder, usually caused by a bacterial infection. The infection causes a frequent urge to urinate, with an accompanying burning sensation during urination. This infection can be treated with antibiotics. Early treatment will prevent the bacteria from ascending into the ureters and causing ureteritis (inflammation of the ureters) and possible kidney infection.
Glomerulonephritis (glom-air-yoo-loh-neh-FRYE-tis) is an inflammation of the kidneys, where the filtration membrane within the renal capsule is infected with bacteria. This can be acute following streptococcal sore throat or scarlet fever infection, or it can be a chronic condition resulting in kidney failure.
Kidney stones, composed of the precipitates of uric acid, magnesium or calcium phosphate, or calcium oxalate, are also known as renal calculi.
The urinary system consists of two kidneys, two ureters, one bladder and one urethrea.
The kidneys are crucial in maintaining homeostasis.
Gout is caused by a high concentration of uric acid in the plasma. cystitis is an inflammation of the urinary bladder.
Glomerulonephritis is an inflammation of the kidneys, where the filtration membrane within the renal capsule is infected with bacteria.
An inflammation of the urinary bladder, usually caused by a bacterial infection, is called cystitis
Kidney stones, composed of the precipitates of uric acid, magnesium or calcium phosphate, or calcium oxalate, are also known as renal calculi
Why are urinary tract infections more common in females? Primarily because of the length of the urethra—in females it is much shorter, enabling bacteria to enter more easily from outside the body.
The major role of maintaining homeostasis with respect to the composition and volume of blood and body fluids is controlled by the kidneys, which perform various functions: 1. Excretion: 2. Maintain blood volume and concentration: 3. pH regulation: 4. Blood pressure: 5. Erythrocyte concentration: 6. Vitamin D production:
The kidneys filter large amounts of fluid from the bloodstream. They are the major excretory organs of the body because they eliminate nitrogenous wastes, drugs and toxins from the body. Although the skin, liver, intestines and lungs also eliminate wastes, they cannot compensate if the kidneys fail. In addition, the kidneys can reabsorb needed substances and return them to the blood.
The kidneys control blood volume by regulating the proper balance in the blood between salts and water. They regulate the volume of urine produced. They also regulate the concentration of ions in body fluids and blood, so the proper balance of sodium, chloride, potassium, calcium and phosphate ions is maintained.
The kidneys control the proper balance of hydrogen ions in the blood, thus helping to regulate the proper pH levels in the body along with buffers in the blood and the respiratory system.
The kidneys produce the enzyme renin (REN-in), which helps adjust filtration pressure.
The kidneys produce erythropoietin (eh-rith-roh-POY-eh-tin), a hormone that stimulates red blood cell production in red bone marrow. They help regulate the concentration of erythrocytes in the blood in cases of chronic hypoxia.
The kidneys convert vitamin D to its active form (calciferol). Vitamin D is important for normal bone and teeth development. It also helps control calcium and phosphorus metabolism. The kidneys participate, along with the liver and the skin, in vitamin D synthesis.
The elimination of wastes by the kidneys is called excretion.
The kidneys regulate the concentration of ions in body fluids and blood.
The regulation of hydrogen ions is pH regulation.
The enzyme renin helps regulate blood pressure
The liver, the skin and the kidneys all participate in the synthesis of vitamin D
The major role of maintaining homeostasis with respect to the composition and volume of blood and body fluids is performed by the kidneys
The hormone produced by the kidneys that stimulates the production of red blood cells in the red bone marrow is erythropoietin
The enzyme produced by the kidneys that helps regulate blood pressure is rennin
The active form of vitamin D is known as calciferol
The kidneys are paired organs that are reddish in color and resemble kidney beans in shape. They are about the size of a closed fist. They are located just above the waist between the parietal peritoneum and the posterior wall of the abdomen. This placement of the kidneys is also referred to as retroperitoneal. The right kidney is slightly lower than the left because of the large area occupied by the liver.
The average adult kidney measures about 11.25 cm (4 inches) long, 5.0 to 7.5 cm (2-3 inches) wide and 2.5 cm (1 inch) thick. Near the center of the concave border of the kidney is a notch called the hilum (HIGH-lum) through which the ureter leaves the kidney. Blood vessels, nerves and lymph vessels also enter and exit the kidney through this hilum. The hilum is the entrance to a cavity in the kidney called the renal sinus, which consists of connective tissue and fat.
Three layers of tissue surround each kidney. The innermost layer is the renal capsule. It is a smooth, transparent, fibrous connective tissue membrane that connects with the outermost covering of the ureter at the hilum. It functions as a barrier against infection and trauma to the kidney. The second layer, on top of the renal capsule, is the adipose capsule. It is a mass of fatty tissue that protects the kidney from blows. It also firmly holds the kidney in place in the abdominal cavity. The outermost layer is the renal fascia (REE-nal FASH-ee-ah), which consists of a thin layer of fibrous connective tissue that also anchors the kidneys to their surrounding structures and to the abdominal wall.
A frontal section through a kidney will reveal an outer area called the cortex and an inner area known as the medulla. In a freshly dissected kidney, the cortex would be reddish in color and the medulla reddish-brown. Within the medulla are 8 to 18 striated, triangular structures called the renal pyramids. The striated appearance is caused by an aggregation of straight tubules and blood vessels. The bases of the pyramids face the cortex and their tips, called the renal papillae (REE-nal pah-PILL-ay), point toward the center of the kidney.
The cortex is the smooth textured area that extends from the renal capsule to the bases of the renal pyramids. It also extends into the spaces between the pyramids. This cortical substance in between the renal pyramids is called the renal columns. Together, the cortex and the renal pyramids make up the parenchyma (par-EN-kih-mah) of the kidney. Structurally, this parenchyma consists of millions of microscopic collecting tubules called nephrons (NEFF-ronz). The nephrons are the functional units of the kidney. They regulate the composition and volume of blood and form the urine.
A funnel-shaped structure called the minor calyx (MYE-nohr KAY-liks) surrounds the tip of each renal pyramid. There can be 8 to 18 minor calyces. Each minor calyx collects urine from the ducts of the pyramids. Minor calyces join to form major calyces. There are two or three major calyces in the kidney. The major calyces join together to form the large collecting funnel called the renal pelvis, which is found in the renal sinus. It is the renal pelvis that eventually narrows to form the ureter (YOO-reh-ter). Urine drains from the tips of the renal pyramids into the calyces. It then collects in the renal pelvis and leaves the kidney through the ureter.
There are three layers of tissue surrounding each kidney.
The smooth, transparent, fibrous connective tissue membrane connecting with the outermost covering of the ureter is the renal capsule

The mass of fatty tissue is the adipose capsule

The tips of the cortex are the renal papillae

The cortex and the renal columns make up the parenchyma of the kidney.

The minor calyces collect urine
Urine leaves the kidney through the ureter
The notch through which the ureter leaves the kidney, and blood vessels, nerves, and lymph vessels enter and exit the kidney, is known as the hilum
A frontal section through the kidney will reveal an outer area called the cortex and an inner area known as the medulla
The funnel-shaped structure that surrounds the tip of each renal pyramid and collects urine from the ducts of the pyramids is called the minor calyx
The functional units of the kidney are the nephrons. Basically, a nephron is a microscopic renal tubule, which functions as a filter, and its vascular (surrounding blood vessels) component. The nephron begins as a double-walled globe known as Bowman’s glomerular capsule. This is located in the cortex of the kidney. The innermost layer of the capsule is known as the visceral layer and consists of epithelial cells called podocytes (POH-doh-sightz). This visceral layer of podocytes surrounds a capillary network known as the glomerulus (glom-AIR-you-lus). The outer wall of Bowman’s glomerular capsule is known as the parietal layer.
A collecting space separates the inner visceral layer from the outer parietal layer of the capsule. Together, Bowman’s glomerular capsule and the enclosed glomerulus make up what is called a renal corpuscle.
The visceral layer of Bowman’s capsule and the endothelial capillary network of the glomerulus form an endothelial-capsular membrane, which is the site of filtration of water and solutes from the blood. This filtered fluid now moves into the renal tubule.
Bowman’s capsule opens into the first part of the renal tubule, called the proximal convoluted tubule, located in the cortex. The next section of the tubule is called the descending limb of Henle, which narrows in diameter as it dips into the medulla of the kidney. The tubule then bends into a U-shaped structure known as the loop of Henle.
As the tubule straightens, it increases in diameter and ascends toward the cortex of the kidney. Here it is called the ascending limb of Henle. In the cortex, the tubule again becomes convoluted and is now called the distal convoluted tubule. The distal convoluted tubule ends by merging with a large straight collecting duct. In the medulla, collecting ducts connect with the distal tubules of other nephrons. The collecting ducts now pass through the renal pyramids and open into the calyces of the pelvis through a number of larger papillary ducts, which empty urine into the renal pelvis.
To facilitate filtration, most of the descending limb has thin walls of simple squamous epithelium, and the rest of the nephron and collecting duct is composed of simple cuboidal epithelium. The proximal tubule, ascending limb of Henle and the collecting duct transport molecules and ions across the wall of the nephron. The descending limb of Henle is highly permeable to water and solutes.

Because the nephrons are mainly responsible for removing wastes from the blood and regulating its electrolytes (which are responsible for the acid or alkaline components of blood) and fluid content, they are richly supplied with blood vessels. The right and left renal arteries transport one-quarter of the total cardiac output directly to the kidneys. About 1200 mL of blood passes through the kidneys every minute. This amounts to blood being filtered of wastes approximately 60 times a day.

Just before or immediately after entering the hilum, the renal artery divides into several branches that enter the parenchyma of the kidney in between the renal pyramids. In the renal columns, these branches are called the interlobar arteries.
At the base of the pyramids, the interlobar arteries arch between the cortex and the medulla. Here they are called the arcuate arteries. Branches of the arcuate arteries produce a series of interlobular arteries that enter the cortex and divide into afferent arterioles. Each afferent arteriole takes blood from the renal artery to Bowman’s glomerular capsule, where the arteriole divides into the tangled capillary network known as the glomerulus.

The glomerular capillaries then reunite to form an efferent arteriole that carries blood away from the glomerular capsule. Each efferent arteriole further divides to form a network of capillaries called the peritubular capillaries, which surround the convoluted tubules of the nephron. Eventually, the peritubular capillaries reunite to form an interlobular vein. The filtered blood then drains into the arcuate vein at the base of the pyramid. From the arcuate veins, the blood travels through the interlobar veins that run between the pyramids in the renal columns. The interlobar veins unite at the single right and left renal vein that leave the kidney at the hilum.
The nerve supply to the kidney comes from the renal plexus of the autonomic nervous system. Sympathetic neurons, using norepinephrine, innervate the blood vessels of the kidneys. This stimulation causes constriction of the arteries, resulting in a decrease in blood flow and a decrease in filtrate formation. Thus, there is a decrease in urine formation. Urine volume production increases in response to a decrease in sympathetic innervation to the renal arteries.
Trauma or increased physical activity causes an increase in sympathetic stimulation, resulting in low levels of urine production.
The nephrons carry out a number of important functions. They control blood concentration and volume by removing selected amounts of water and solutes, they help regulate blood pH, they remove toxic wastes from the blood, and they stimulate red blood cell production in red bone marrow by producing a hormone called erythropoietin. The eliminated materials are collectively called urine. Urine is formed by three processes in the nephrons: 1. glomerular filtration 2. tubular reabsorption 3. tubular secretion
In glomerular filtration, the glomerulus filters water and certain dissolved substances from the plasma of blood. This process of glomerular filtration results in increased blood pressure. This increased pressure forces the fluid to filter from the blood. The dissolved substances include positively charged ions of sodium, potassium, calcium and magnesium; negatively charged ions of chloride, bicarbonate, sulfate and phosphate; and glucose, urea and uric acid. This filtrate is mainly water with some of the same components as the blood plasma. No large proteins are filtered. Both kidneys filter about 45 gallons of blood plasma per day. Yet only a small portion of the glomerular filtrate leaves the kidneys as urine. Most fluid gets reabsorbed in the renal tubules and reenters the plasma.
The tubular reabsorption process transports substances out of the tubular fluid and back into the blood of the peritubular capillary. This reabsorption occurs throughout the renal tubule, but the majority of reabsorption occurs in the proximal convoluted tubule. Active transport reabsorbs glucose while osmosis rapidly reabsorbs water. Active transport reabsorbs amino acids, creatine, lactic acid, uric acid, citric acid and ascorbic acid. Active transport also reabsorbs phosphate, calcium, sulfate, sodium and potassium ions. Chloride ions and other negatively charged ions are reabsorbed by electrochemical attraction.
The descending limb of Henle reabsorbs water by osmosis. The ascending limb reabsorbs sodium, potassium and chloride ions by active transport. The distal convoluted tubule reabsorbs sodium ions by active transport and water by osmosis. The collecting ducts of the nephrons also will reabsorb water by osmosis. About 95% of water is reabsorbed back into the bloodstream. Hormones, such as vasopressin and aldosterone, are essential to help control this process.
In tubular secretion, substances will move from the plasma in the peritubular capillary into the fluid of the renal tubule. The amount of a certain substance excreted into the urine may eventually exceed the amount originally filtered from the blood plasma in the glomerulus. The proximal convoluted tubule actively secretes penicillin, creatinine and histamine into the tubular fluid. The entire renal tubule actively secretes hydrogen ions (H+), thus helping to regulate the pH of the body fluids. The distal convoluted tubule and the collecting duct secrete potassium ions (K+).
Urine consists of water and solutes that the kidneys either eliminate or retain in the body to maintain homeostasis. Urine is about 95% water with urea, uric acid, some amino acids and electrolytes. The daily production of urine is between 0.6 and 2.5 liters per day. This depends on a person’s fluid intake, environmental temperature and humidity, respiratory rates, body temperature and emotional conditions. Urine production of 56 mL an hour is considered normal; 30 mL an hour indicates possible kidney failure.
The nephrons are the functional units of the kidney.
The innermost layer of Bowman’s glomerular capsule is made up of cells called podocytes
The endothelial-capsular membrane is the site of filtration of water and solutes from the blood.
The part of Henle that is highly permeable to water and solutes is the descending limb
The kidney is supplied with blood from the left and right renal arteries
About 1200 ml of blood passes through the kidneys every minute.
The interlobar arteries are found in the renal columns
The nerve supply to the kidney comes from the renal plexus
In the medulla of the kidney, the renal tubule bends into a U-shape known as the loop of Henle.
The functional microscopic units of the kidney that act as a filter are the nephrons
The process that transports substances out of the tubular fluid and back into the blood of the peritubular capillary is known as tubular reabsorption
The double-walled globe surrounding the glomerulus of the kidney is called Bowman's glomerular capsule
Jensen is pouring water into his coffeemaker. What particular process of urine formation is he demonstrating? Glomerular filtration
The body has two ureters (YOO-reh-terz) each one descending from a kidney. Each ureter is basically an extension of the pelvis of a kidney and extends about 25 to 30 cm (10 to 12 inches) down to the urinary bladder. Each begins as the funnel-shaped renal pelvis and descends parallel on each side of the vertebral column to the bladder. They connect to the urinary bladder posteriorly.

The principal function of the ureters is to transport urine from the renal pelvis into the urinary bladder. The ureters are lined with a mucous coat of transitional epithelium that can stretch. Connective tissue binds the epithelium to a layer of smooth muscle. The urine is carried through the ureters primarily by peristaltic contractions of the smooth muscular walls of the ureters, but gravity and hydrostatic pressure also contribute. The outermost layer of the ureter is composed of connective tissue called the adventitia. Peristaltic waves pass from the kidney to the urinary bladder varying from one to five waves per minute, depending on the amount of urine formation. Consuming excess liquids will cause more urine formation per unit of time.
The urinary bladder is a hollow muscular organ located in the pelvic cavity posterior to the pubic symphysis. It consists of the same tissue layers as the ureters. It is a movable organ held in position by folds of peritoneum. When empty, it resembles a deflated balloon. It assumes a spherical shape when slightly full of urine. As urine volume increases, it becomes pear-shaped and ascends into the abdominal cavity.

The interior of the bladder has three openings, the two openings from the two ureters and the single opening to the urethra that will drain the bladder. A smooth triangular region of the bladder outlined by these openings is called the trigone (TRY-gohn). Bladder infections tend to develop in this region. The bladder wall contains three layers of smooth muscle collectively known as the detrusor (dee-TRUE-sohr) muscle. At the junction of the urinary bladder and urethra, smooth muscle of the bladder wall forms the internal urinary sphincter, which is under involuntary control.
Urine is expelled from the bladder by an act known as micturition (mik-tyoo-RIH-shun), commonly referred to as urination or voiding. This response is caused by a combination of involuntary and voluntary nerve impulses. The average capacity of the bladder is 700 to 800 mL. When the amount of urine reaches 200 to 400 mL, stretch receptors in the bladder wall transmit nerve impulses to the lower portion of the spinal cord. It is these impulses that initiate a conscious desire to expel urine and an unconscious reflex called the micturition reflex.
During urination, the detrusor muscle of the bladder contracts as do the muscles of the pelvic floor and abdominal wall. The external urinary sphincter, formed of skeletal muscle that surrounds the urethra as it leaves the bladder, must relax and urine then leaves the bladder and moves through the urethra to the outside.
The urethra (yoo-REE-thrah) is a small thin-walled tube leading from the floor of the urinary bladder to the outside of the body. It transports urine by peristalsis. Its position in the two sexes differs slightly as does its function.
In females, it lies directly posterior to the pubic symphysis and is located in the wall of the vagina in an anterior position just above the vaginal opening. Its length is about 3.8 cm (1.5 inches). Its opening to the outside is called the urethral orifice and is located between the clitoris and the vaginal opening.

In males, the urethra is 20 cm (8 inches) long. Directly below the bladder, it passes vertically through the prostate gland. It then passes through the urogenital diaphragm and enters the penis. It opens at the tip of the penis at the urethral orifice. In the male, the urethra has a dual function as part of both the urinary and reproductive systems. It carries urine out of the body and functions as a passageway for semen to be discharged from the body.
The bladder wall has three layers of smooth muscle known as the detrusor muscle.
Micturition is precipitated by bladder stretch receptors
Urine in the urethra is transported by peristalsis
Urine is expelled from the body by an act called micturition, commonly known as urination or voiding.
The urethra is the thin-walled tube through which urine leaves the bladder and exits to the outside of the body.
The principal function of the ureters is to transport urine from the renal pelvis into the urinary bladder.

The smooth triangular region of the bladder outlined by the three openings into the bladder, which consists of the two openings of the ureters and the one opening of the urethra, is called the trigone
Alvaro injured his spinal cord and is now paralyzed from the waist down. He has to wear a urinary catheter because he has no control over which urination muscle? The external urethral sphincter
Integumentary System 1. The skin and the kidneys are involved in vitamin D production. 2. The skin is a protective barrier and a site for water loss via perspiration. 3. The urinary system compensates for water loss caused by perspiration.

Skeletal System 1. The lower ribs provide some protection to the kidneys. 2. Both the kidneys and bones help maintain calcium levels in the blood.

Muscular System 1. Muscles control elimination of urine from the bladder in the voluntary action of micturition. 2. Muscle cells produce creatinine as a nitrogenous waste product of metabolism that the kidneys excrete.

Nervous System 1. The nervous system controls urine production and micturition.

Endocrine System 1. Antidiuretic hormone (ADH) and aldosterone help regulate urine production by influencing renal reabsorption of electrolytes and water.

Cardiovascular System 1. Blood volume is controlled by the urinary system. 2. Blood pressure controls glomerular filtration. 3. Blood carries nutrients and oxygen to and eliminates waste from the urinary tissues.

Lymphatic System 1. The kidney helps maintain extracellular fluid composition and volume. 2. Lymphatic vessels help maintain blood pressure by returning lymph to the plasma of blood. 3. The lymphocytes help protect the urinary structures from infection and cancer.

Digestive System 1. The liver transforms toxic ammonia (a by-product of amino acid metabolism) into less harmful urea that is then excreted by the kidneys. 2. The kidneys restore fluids lost by the digestive process.

Respiratory System 1. The lungs and the kidneys help maintain the proper pH of the body. 2. The respiratory system provides the oxygen needed by the cells of the kidneys to function and eliminates the carbon dioxide waste product.

Reproductive System 1. The urethra of the male functions as both an organ to eliminate urine from the bladder and as a tube to transfer sperm to the outside. 2. The kidneys replace fluid lost from the normal activities of the reproductive system.
CHAPTER 19
At its most basic level, reproduction is the process by which a single cell duplicates its genetic material. This is the process of mitosis, discussed in Chapter 4. Mitosis allows us to grow and repair damaged or old tissues. In this sense, cellular reproduction enables us to maintain ourselves.
However, reproduction is also the process by which our genetic material is passed on from one generation to the next. This process requires a special kind of cellular reproduction that produces special cells, the sperm from the male and the egg from the female. These join in the process of fertilization to produce a fertilized egg, or zygote. The special type of cellular division that produces the sex cells is called meiosis. Meiosis, you will recall, is a reduction division of the genetic material. This results in an egg carrying 23 chromosomes and the sperm carrying 23. When fertilization occurs, the resulting zygote will possess the full complement of 46 chromosomes.
This chapter discusses the organs of the reproductive system that produce the sex cells, transport and nurture their development. Once an egg is fertilized by a sperm, the resulting zygote will develop into an embryo in the uterus of the female and grow by the process of mitosis into a fetus. The fetus will continue to develop until birth. The purpose of the reproductive system is to produce offspring and ensure the perpetuation of the human species.
Cell division resulting in the egg and sperm each carrying 23 chromosomes is called meiosis.
Immediately following the union of sperm and egg, the fertilized egg is designated a zygote
A bacterial infection of the uterus, uterine tubes, or ovaries that can lead to sterility if untreated is known as pelvic inflammatory disease
A condition in which the foreskin of the penis fits too tightly over the head and cannot be retracted is known as phimosis
A series of symptoms that develop in many women before the menstrual cycle, which include irritability, tiring easily, becoming highly nervous, and feeling depressed is known as premenstrual syndrome
The primary sex organs of the male reproductive system are the testes (TES-teez) or male gonads. These organs produce sperm and the male sex hormones. There are also accessory organs, like the scrotum, that support the testes. Other accessory structures nurture the developing sperm cells and various ducts store or transport the sperm to the exterior or into the female reproductive tract. Accessory glands add secretions that make up the semen. A transporting and supporting structure is the penis.
The scrotum (SKROH-tum) is an outpouching of the abdominal wall. It consists of loose skin and superficial fascia. It is the supporting structure of the testes. Externally, it appears as a single pouch of skin separated into lateral portions by a median ridge known as the raphe (RAY-fee). Internally, it is separated into two sacs by a septum. Each sac contains a single testis (TES-tis). The testes (plural) produce the sperm and the male sex hormones. Because sperm and hormone production and survival require a temperature lower than normal body temperature, the scrotum lies outside the body cavity. Its environment is about 3°F below body temperature.
Exposure to cold, as in winter, causes contraction of the smooth muscle fibers, moving the testes closer to the pelvic cavity so they can absorb more body heat. The whole scrotal sac contracts and a muscle, the cremaster (kree-MASS-ter) muscle, located in the spermatic cord, elevates the testes. Exposure to heat, as on a hot summer day, reverses the process, and the scrotal sac hangs well below the pelvic cavity to avoid body warmth.

The testes are paired oval glands measuring about 5 cm (2 inches) in length and 2.5 cm (1 inch) in diameter. They are covered by a dense layer of white fibrous connective tissue called the tunica (TYOO-nih-kah) albuginea (al-byoo-JEN-ee-ah) that extends inward and divides each testis into a number of smaller, internal compartments known as lobules. Each lobule contains one to three tightly coiled tubules called the convoluted seminiferous (sem-in-IF-er-us) tubules.

These seminiferous tubules actually produce the sperm by a process called spermatogenesis (spur-mat-oh-JEN-eh-sis).
Spermatogenesis begins in the seminiferous tubules, as the most immature sperm cells called spermatogonia (spur-mat-oh-GO-nee-ah) begin to divide by mitosis to produce daughter cells called primary spermatocytes (PRYE-mary spur-MAT-oh-sightz). The primary spermatocytes undergo the cellular reduction division called meiosis. After the first meiotic division (review Chapter 4), the primary spermatocytes become secondary spermatocytes and their genetic information has been reduced in half (chromosomes are reduced from 46 to 23). These secondary spermatocytes now undergo the second meiotic division and become spermatids (SPUR-mah-tidz). These spermatids will eventually mature into sperm cells.
Found among the developing sperm cells in the seminiferous tubules are the Sertoli (Sir-TOH-lee) cells. They produce secretions that supply nutrients for the developing sperm cells, or spermatozoa (spur-mat-oh-ZOH-ah).
In the lobules of the testes, between the seminiferous tubules in the soft connective tissue are clusters of interstitial (in-ter-STISH-al) cells of Leydig (SELZ of LYE-dig). The interstitial cells of Leydig produce the male sex hormone testosterone.
Thus, we see that two different areas of the testes produce two different products through two different groups of cells. The primary spermatocytes in the seminiferous tubules produce sperm, and the interstitial cells of Leydig in the tissue of the lobules around the tubules produce testosterone. Because the testes produce both sperm and testosterone, they are both exocrine (glands with ducts) and endocrine (without ducts) glands.

The spermatozoa, or mature sperm cells, are produced at a rate of about 300 million per day. Once ejaculated, they have a life expectancy of about 48 hours in the female reproductive tract. They will not survive very long at all outside the female reproductive tract in the external environment. They are highly adapted for reaching and penetrating a female egg or ovum. Each sperm is composed of a head, a middle piece and a tail.

The head, which developed from the nucleus of a spermatid cell, contains the genetic material and an acrosome (ak-roh-SOHM). The acrosome contains enzymes that aid the sperm cell in penetrating the covering of the female egg cell or ovum. The rest of the sperm cell develops from the cytoplasm of the spermatid cell. The middle piece contains numerous mitochondria, which produce the high-energy molecule adenosine triphosphate (ATP) that provides the energy for locomotion. The tail of the sperm cell is a typical flagellum. The flagellum beats, from the energy of the ATP molecule, and propels the sperm as it swims its way up the female reproductive tract in search of an ovum.

Testosterone (tess-TOSS-ter-ohn) has a number of effects on the male body. It controls the development, growth and maintenance of the male sex organs. Just before birth, it causes the descent of the testes from the abdominal cavity into the scrotal sac.

During puberty, it stimulates bone growth, resulting in the development of broad shoulders and narrow hips. It stimulates protein buildup in muscles, producing muscular development, typical of males with more bulk and firmness in their muscular physique. Testosterone stimulates maturation of sperm cells. It causes enlargement of the thyroid cartilage, resulting in the visible Adam’s apple in males and the deepening of the voice with its low range of pitch.

Other secondary male sex characteristics are also influenced by the production of testosterone. These include aggressive behavior and body hair patterns. Body hair patterns include the development of chest hair and axillary hair within hereditary limits, facial hair and temporal hairline recession.

As the sperm cells are formed, they are moved from the convoluted seminiferous tubules in the testis to the straight tubules at the tip of each lobule. Here the convoluted seminiferous tubules become linear and lose their convolutions. These lead to a network of ducts in the testis called the rete (REE-tee) testis. The sperm are now transferred out of the testis through a series of coiled efferent ducts that empty into a single tube known as the ductus epididymis.

The epididymis is a comma-shaped structure located along the posterior border of a testis, consisting principally of a tightly coiled tube called the ductus epididymis. The epididymis is the site where the sperm cells continue to mature. The tube is about 20 feet long and it takes the sperm about 20 days to move through this tube. The tube stores the maturing sperm cells while they develop their swimming capability via their flagella. The tube propels the sperm toward the next part of the system during ejaculation, when the smooth muscle of the wall of the tube contracts by peristalsis.
The next part of the duct system is the ductus deferens (DUCK-tus DEF-er-enz), or the vas deferens. Within the tail of the epididymis, the ductus epididymis becomes less and less convoluted. At this point it is now referred to as the ductus or vas deferens. It is also commonly called the seminal duct.
It is approximately 18 inches long and ascends the posterior border of the testis, penetrates the inguinal canal and enters the pelvic cavity where it loops over the side and down the posterior surface of the urinary bladder. The tube is enclosed in a connective tissue sheath along with nerves and blood vessels. This sheath is called the spermatic cord. The end of the ductus or vas deferens has a dilated terminal portion known as the ampulla. Each ductus deferens empties into its ejaculatory duct, the next part of the system.
When a vasectomy (vas-EK-toh-mee) is performed for birth control, the physician performs this minor operation by making an incision into the scrotal sac to cut or cauterize the ductus or vas deferens. The testes still produce sperm but they are now unable to make their way to the outside of the system. They eventually die and are reabsorbed by the body. A man becomes sterile by this procedure, but fluids are still produced and are ejaculated during intercourse. The male libido is not affected, erections and ejaculations still occur, but there are no sperm in the semen. In addition, because testosterone is still being produced, all the secondary male sex characteristics are maintained.

The next part of the tube is the ejaculatory duct. Posterior to the urinary bladder, each ductus deferens joins its ejaculatory duct. Each duct is about 1 inch long. The ducts eject spermatozoa into the urethra. The urethra is the terminal duct of the system. It serves as a common passageway for both spermatozoa coming from the testes and urine coming from the bladder.
In the male, the urethra (YOO-ree-thrah) passes through the prostate gland, the urogenital diaphragm and the penis. It is about 8 inches long and is subdivided into three parts: 1. the prostatic urethra, which is surrounded by the prostate gland and is about 1 inch long; 2. the membranous urethra about ½ inch long, which runs from the prostatic urethra to the penis; and 3. the spongy or cavernous urethra, found within the penis and about 6 inches long, but varies according to the size of the penis. The spongy urethra enters the head or bulb of the penis and terminates at the male urethral orifice.

The accessory glands include the two seminal vesicles, the prostate gland and the paired bulbourethral glands. These glands secrete the liquid portion of the semen, the sperm-containing fluid that is produced during ejaculation.
The paired seminal vesicles (SEM-ih-nal VESS-ih-kulz) are convoluted pouchlike structures approximately 2 inches in length. They are located posterior to and at the base of the urinary bladder in front of the rectum. They produce the alkaline, viscous component of semen that is rich in the sugar fructose and other nutrients for the sperm cells and pass it into the ejaculatory duct. They produce about 60% of the volume of semen. Because the duct of each seminal vesicle joins the ductus deferens on each side to form the ejaculatory duct, sperm and seminal fluid together enter the urethra during ejaculation.
The prostate gland is a single, doughnut-shaped gland about the size and shape of a chestnut. It surrounds the superior portion (the prostatic urethra) of the urethra just below the bladder. It also secretes an alkaline fluid that makes up about 13% to 33% of semen. Its fluid plays a role in activating the sperm cells to swim. The fluid enters the prostatic urethra through several small ducts. The prostate gland is located anterior to the rectum and a physician can feel its size and texture by digital examination through the anterior wall of the rectum.
The paired bulbourethral (BUL-boh-yoo-REE-thral) glands, also known as Cowper’s glands, are about the size of peas. They are located beneath the prostate gland on either side of the membranous urethra. They secrete thick, viscous, alkaline mucus. Their ducts connect with the spongy urethra. This secretion is the first to move down the urethra when a man becomes sexually aroused and develops an erection. It functions as both a lubricant for sexual intercourse and as an agent to clean the urethra of any traces of acidic urine.
Semen, also known as seminal fluid, is a mixture of sperm cells and the secretions of the seminal vesicles, the prostate and the bulbourethral glands. The fluid is milky in color and sticky, due to the fructose sugar that provides the energy for the beating flagellum of each sperm cell. The semen is alkaline, with a pH of 7.2 to 7.6. This neutralizes the acidity of the female vagina and the male urethra and helps protect the sperm cell. The semen provides a transport medium for the swimming sperm cells.

The average volume of semen per ejaculation is 2.5 to 6 mL, and the average range of spermatozoa ejaculated is 50 to 100 million/mL. If the number of spermatozoa falls below 20 million/mL the man is considered to be sterile. Semen contains enzymes that activate sperm after ejaculation. The semen also contains an antibiotic called seminalplasmin (SEM-ih-null-PLAZ-min), which has the capability of destroying certain bacteria. Because the female reproductive tract and the semen contain bacteria, the seminalplasmin helps keep these bacteria under control and thus helps protect the sperm and ensure fertilization.
The penis (PEE-nis) is used to introduce or deliver spermatozoa into the female reproductive tract by being inserted into the vagina. The penis consists of a shaft whose distal end is a slightly enlarged region called the glans penis or head, which means “shaped like an acorn.” Covering the glans penis is a section of loose skin called the prepuce (PRE-pyoose) or foreskin. Occasionally, the foreskin is removed at birth by a surgical procedure called circumcision. This will be done if the foreskin does not pull back completely over the glans penis, resulting in future hygiene problems. If the skin is loose and pulls back, circumcision is not necessary. It is also done as a rite in certain religions.
Internally, the penis is composed of three cylindrical masses of spongy tissue containing blood sinuses. During sexual stimulation, the arteries that supply the penis dilate, and large quantities of blood enter these blood sinuses. Expansion of these sinuses compress the veins that would normally drain the penis so that most of this entry blood is retained. These changes in blood vessels produce an erection, which helps the penis penetrate the female vagina. Once sexual stimulation ceases, the arteries supplying the blood constrict and the veins drain the blood, resulting in the penis going limp and the end of the erection.
During ejaculation, the smooth muscle sphincter at the base of the urinary bladder is closed. This ensures that urine is not expelled during ejaculation and that semen does not enter the urinary bladder.
When producing sperm, the testes are considered exocrine glands.
When the testes are producing the hormone testosterone, they are endocrine glands.
The testes are raised and lowered in reaction to changes in temperature
The inside of the scrotum has two sacs which are separated by a septum.
The tunica albuginea extends inward and divides the testes into small compartments called lobules.
In the testicular lobules are found the seminiferous tubules
Meiosis occurs in the primary spermatocytes
Sertoli cells provide nutrients for the sperm, and the interstitial cells of Leydig produce testosterone.
The acrosome contains enzymes, which help the sperm penetrate the ovum.
Mitochondria provide energy for the flagellum (or tail) of the sperm, which propels it on its journey.
The straight tubules lead to the rete testis
The sperm leave the testes through the efferent ducts and enter the ductus epididymis
The seminal duct is another name for the vas deferens
The part of the urethra found in the penis is the cavernous (or spongy) urethra.
Three sets of accessory glands add secretions to the semen. The ones contributing the most are the seminal vesicles
Protection of the sperm against bacteria is the function of seminalplasmin
Cara and Nicholas had been trying to have children for 2 years with no success. At the first appointment with the infertility specialist, they found that Nicholas had a low sperm count. He was surprised by the doctor’s first piece of advice—to wear boxers instead of briefs. How could wearing boxer shorts affect sperm production? Sperm are produced and survive better at a few degrees below body temperature. Boxer shorts will keep the testicles farther away from the body—and thus at a lower temperature.

The primary sex organs of the female reproductive system are the ovaries (OH-vah-reez), or female gonads. These organs produce eggs, or ova, as exocrine glands and as endocrine glands produce the female sex hormones estrogen (ESS-troh-jen) and progesterone (proh-JESS-ter-ohn). The accessory organs of the system are the uterine or fallopian tubes, the uterus, the vagina and the external genitalia. Some accessory glands also produce mucus for lubrication during sexual intercourse. The female system is more complex hormonally than the male system because it must also nurture the developing fetus during pregnancy.
The ovaries or female gonads are paired glands about the size of unshelled almonds. They are found in the upper pelvic cavity, one on each side of the uterus.

They are held in position by a series of ligaments. Suspensory ligaments secure the ovaries to the lateral walls of the pelvis. Ovarian ligaments anchor the ovaries medially. In between, they are held in place and enclosed by the broad ligament, which is a fold of peritoneum. A microscope view of an ovary reveals that each one consists of a number of parts.
The surface of an ovary is covered with germinal epithelium. The capsule of an ovary consists of collagenous connective tissue known as the tunica albuginea. This is divided into an outer area called the cortex of the stroma and contains ovarian follicles in various stages of development and an inner area called the stroma of the medulla.

Ovarian follicles are eggs or ova and their surrounding tissues in various stages of development. Each follicle contains an immature egg or oocyte (OH-oh-sight) and at this stage is referred to as a primary follicle. As the developing egg begins to mature, the follicle increases in size and develops a fluid-filled central region called the antrum. At this stage the follicle is called a secondary follicle as it begins to develop the fluid.
A mature follicle with a mature egg is called a graafian (GRAF-ee-an) follicle. This is basically an endocrine gland that begins to secrete estrogen and is ready to eject the mature egg, an event known as ovulation. After the egg ruptures from the mature graafian follicle, the follicle changes into the corpus luteum (KOR-pus LOO-tee-um), or yellow body, which produces estrogen and progesterone and eventually degenerates to become the corpus albicans (KOR-pus AL-bih-konz), or white body.
The function of the ovaries is to produce eggs or ova, discharge the ova in ovulation and secrete the female sex hormones estrogen and progesterone. The rest of the female system consists of ducts that transport and nurture the egg and, if fertilization occurs, delivers the fetus to the outside world during birth. The duct system consists of the uterine or fallopian tubes, the uterus and the vagina.
Oogenesis (oh-oh-JEN-eh-sis) or formation of the female sex cells or eggs occurs in the ovaries. In males the process is called spermatogenesis and occurs in the seminiferous convoluted tubules of the testes. In males, the process begins at puberty and men can produce sperm throughout their lives. In women, the process begins at puberty but ends at menopause around the age of 50. In addition, the total number of eggs that a woman can produce and release is determined at birth.

In a developing female fetus, the female stem cells called oogonia (oh-oh-GO-nee-ah) divide by mitosis to produce primary oocytes (PRYE-mary oh-oh-sightz). They become surrounded by follicular cells in the ovary and are now part of the primary follicles. Around 700,000 are produced at this time and represent the total number of eggs that a female could produce during her reproductive years. They now await further development until puberty.

At puberty, the ovarian cycle is stimulated when the anterior pituitary gland secretes follicle-stimulating hormone (FSH). Only a small number of primary follicles will grow and develop, with only one egg being released each month. Only about 450 eggs will be produced from the store of 700,000 primary oocytes through the process of meiosis.
After the first meiotic division the primary oocyte becomes two cells. The secondary oocyte is the larger of the two cells; a very small cell called the polar body is nonfunctional. During the second meiotic division, which occurs only after fertilization, the secondary oocyte and the polar body divide again and the secondary oocyte becomes an ootid (OH-oh-tid), or mature egg cell, and due to unequal division of the cytoplasm another polar body is formed. The first polar body from the first meiotic division again divides in the second meiotic division to become two nonfunctional polar bodies. After the second meiotic division, one functional egg cell is produced and three nonfunctional polar bodies.

This is very different from meiosis in men, in whom four functional sperm cells are produced. However, the sperm cells are very tiny with few stored nutrients and will not survive very long because they must get their nutrients from the seminal fluid. The egg cell, however, has lots of stored food because it is a large cell and can supply the developing embryo until it embeds itself in the endometrial lining of the uterus.
The female body contains two uterine (YOO-ter-in) or fallopian (fah-LOH-pee-an) tubes that transport the ova from the ovaries to the uterus. There is a funnel-shaped open end to each tube called the infundibulum (in-fun-DIB-yoo-lum). This lies close to an ovary but does not attach to it. The infundibulum is surrounded by a fringe of finger-like projections called the fimbriae (FIM-bree-ee) that partially surround an ovary. Approximately once a month an ovum ruptures from the surface of an ovary near the infundibulum of the uterine tube, a process called ovulation.

The ovum is swept by ciliary action of the epithelium of the infundibulum and by the waving fimbriae, which create a current that carries the egg into the uterine tube. The ovum is then moved along the uterine tube by the action of the cilia and by wavelike peristaltic contractions of the smooth muscle of the uterine tube. If the egg is fertilized, it usually occurs in the upper third of the uterine tube. This means that the sperm must swim up through the vagina, into the uterus, and then up two-thirds of the uterine tube.
Fertilization may occur at any time up to about 24 hours following ovulation. If fertilized, the ovum will make its journey down the uterine tube and enter the uterus within 7 days.

The uterus (YOO-ter-us) or womb is located in the pelvic cavity between the rectum and the urinary bladder. It is held in position by a series of ligaments, and it is the site of menstruation. The uterus is where the fertilized egg is implanted, the fetus develops during pregnancy and where labor begins during delivery. It is shaped like an inverted pear and can greatly increase in size during pregnancy to accommodate the developing fetus. It will extend well above the navel or umbilicus in the late stages of pregnancy.
Its anatomic divisions include the dome-shaped portion above the uterine tubes called the fundus (FUN-dus). Its major portion is the central tapering region known as the body of the uterus. The narrow inferior portion that opens into the vagina is called the cervix. Between the body and the cervix is a small constricted region called the isthmus (ISS-mus). The interior of the body of the uterus is known as the uterine cavity; the interior of the narrow cervix is known as the cervical canal. The junction of the uterine cavity with the cervical canal is called the internal os and the opening of the cervix into the vagina is called the external os.

The wall of the uterus is made of three layers of tissue. The innermost layer is the endometrium (en-doh-MEE-tree-um). This mucosal layer is where the fertilized egg burrows into the uterus, a process called implantation. The middle layer of the uterus is called the myometrium (my-oh-MEE-tree-um), which consists of smooth muscle important during delivery to move the child out of the womb. The outermost layer is the perimetrium (pair-ih-MEE-tree-um) made of serous membrane and also known as the visceral peritoneum. When a woman is not pregnant the endometrial lining of the uterus is shed approximately every 28 days in the process called menstruation.
The menstrual (MEN-stroo-al) cycle, also known as the menses (MEN-seez) or menstruation (men-stroo-AY-shun), is the cyclical shedding of the lining of the uterus in response to changes in hormonal levels. The cycle varies from woman to woman within a range of 24 to 35 days. To discuss the events occurring during the cycle, we will assume an average duration of 28 days. Events occurring during the cycle can be divided into three phases: the menstrual phase, the preovulatory or proliferative phase, and the postovulatory or secretory phase.

The menstrual phase. This phase is also known as menstruation or menses. It lasts from day 1 to 5. During this time, the thick endometrial lining of the uterus is shed along with tissue fluid, blood, mucus and epithelial cells. Bleeding during this period can last from 3 to 5 days. The detached tissues and blood exit through the vagina as the menstrual flow.
During this phase, the ovarian cycle is also in operation. The ovarian follicles, known as primary follicles, begin their development. During the early phase of each menstrual cycle, 20 to 25 primary follicles begin to produce very low levels of estrogen. A clear membrane, the zona pellucida, also develops around the eggs. Later on in the phase at day 4 to 5, about 20 of the primary follicles develop into secondary follicles. These secrete a follicular fluid that forces the ovum to the edge of the secondary follicle. Although a number of follicles begin development during each cycle, only one attains maturity through the process of meiosis. The other follicles undergo cellular death or atresia.

The preovulatory or proliferative phase. This phase is more variable in length. It will last from day 6 to 14 in our 28-day cycle. During this phase, only one of the secondary follicles in the ovary matures into a graafian follicle. This follicle contains a mature egg and will discharge the egg in a process called ovulation. Rising estrogen levels produced by the follicles cause the endometrial lining to thicken during this phase.

Ovulation is the rupturing of the graafian follicle. Refer to the figure below. The ovum is released into the pelvic cavity and this process occurs on day 14 in our 28-day cycle. After ovulation, the graafian follicle collapses and blood within it forms a clot called the corpus hemorrhagicum (KOR-pus hem-oh-RAJ-ih-kum). This clot is eventually absorbed by the remaining follicular cells. Eventually these cells enlarge, change structure and form the corpus luteum or yellow body.
The postovulatory or secretory phase. This phase is the most constant in duration and lasts from days 15 to 28 in our 28-day cycle. It represents the time between ovulation and the onset of the next menstrual cycle. After ovulation occurs, the level of estrogen in the blood drops slightly and secretion of luteinizing hormone (LH) stimulates the development of the corpus luteum. The corpus luteum now begins to secrete increasing quantities of both estrogen and progesterone. The progesterone prepares the endometrium to receive a fertilized ovum by causing it to increase in size and to secrete nutrients into the uterine cavity.

If fertilization and implantation do not occur, the rising levels of progesterone and estrogen from the corpus luteum inhibit luteinizing hormone-releasing hormone (LHRH) from the hypothalamus and LH from the anterior pituitary gland. As a result, the corpus luteum degenerates and becomes the corpus albicans. This will initiate another menstrual cycle.
If fertilization and implantation do occur, the corpus luteum will be maintained for about 4 months. During this time, it continues to secrete estrogen and progesterone. The corpus luteum is maintained by human chorionic gonadotropin, a hormone produced by the developing placenta. Once the placenta is developed, it will secrete estrogen to support pregnancy and progesterone to both support pregnancy and to cause breast development for milk production in the mammary glands.

The length of a menstrual cycle is variable. It can be as long as 40 days or as short as 21 days. It normally occurs once each month from menarche (men-AR-kee), which is the first menstrual cycle, to menopause (MEN-oh-pawz), which is the last menstrual cycle. Even though a woman may have a regular menustrual cycle, she may not necessariily be ovulating or releasing an egg. This may lead to problems with fertility and conception.

The ovaries actually produce several types of estrogens: estradiol, which is the most abundant and is mainly responsible for the effects of estrogen on the body, and estrone and estriol. The ovaries become active during puberty, producing ova and estrogens. The estrogens cause the development of the secondary sex characteristics of a female. In addition to enlargement of the uterine tubes, uterus, vagina and external genitalia of the female, estrogens cause the development of the breasts and the appearance of pubic hair and axillary hair under the arms. Fat gets deposited under the skin, resulting in the soft look of a female. In particular, more fat is deposited around the hips and breasts. The pelvic bone widens and the onset of the menstrual cycle begins.

The vagina (vah-JEYE-nah) has a number of functions. It serves as a passageway for the menstrual flow. It is the receptacle for the penis during sexual intercourse, or coitus (KOH-ih-tus). It also is the lower portion of the birth canal. There is a recess called the fornix (FOR-niks), which surrounds the vaginal attachment to the cervix. The dorsal recess is called the posterior fornix and is slightly larger than the two lateral fornices and the ventral fornix. The fornix can accommodate the placing of a contraceptive diaphragm, which prevents sperm from entering the uterus.
The reproductive structures located external to the vagina are referred to as the external genitalia of the female. The term vulva (VULL-vah), or pudendum, (pyoo-DEN-dum) is a collective term for these structures. They include the mons pubis, labia majora, labia minora, clitoris, urethral and vaginal openings and the vestibular glands.
The mons pubis, also called the veneris (veh-NEER-is), is a mound of elevated adipose tissue that becomes covered with pubic hair at puberty. It is situated directly over the pubic symphysis. From the mons pubis, extending posteriorly and inferiorly are two longitudinal folds of hair-covered skin called the labia majora (LAY-bee-ah mah-JOR-ah). This is the female homologue to the male scrotum. These two folds of skin contain an abundance of adipose tissue and sweat glands. Medial to the labia majora are two other delicate folds of skin called the labia minora (LAY-bee-ah mih-NOR-ah). The labia minora do not have hair and have just a few sweat glands, but possess numerous sebaceous glands.
The clitoris (KLIT-oh-ris) is a small, cylindrical mass of erectile tissue with nerves found at the anterior junction of the labia minora. There is a layer of skin called the prepuce or foreskin formed at the point where the two labia minora join and cover the body of the clitoris. The exposed portion of the clitoris is the glans. The clitoris is the female homologue to the male penis. It, too, is capable of enlargement by becoming swollen with blood during sexual stimulation and excites the female. Unlike the penis, it does not have an internal duct.

The opening or region between the two labia minora is called the vestibule. Within the vestibule is a thin fold of tissue called the hymen (HIGH-men), which partially closes the distal end of the vagina. This fold of mucosa is highly vascularized and bleeds when ruptured during the first sexual intercourse. It occasionally is torn during a sports activity or on insertion of a tampon. Also located in the vestibule are the vaginal orifice and the urethral orifice plus the openings of several ducts coming from the vestibular glands.
Posterior to and on either side of the urethral orifice are the two openings of the ducts of the lesser vestibular or Skene’s glands. These glands are homologous to the male prostate gland and they secrete mucus. On both sides of the vaginal orifice are the openings of two small glands called the greater vestibular or Bartholin’s glands. These glands are homologous to the male’s Cowper’s glands and also secrete mucus. The mucus secreted by these vestibular glands lubricates the distal end of the vagina during sexual intercourse.

The perineum (pair-ih-NEE-um) is a diamond-shaped area at the inferior end of the trunk between the buttocks and thighs of both males and females. It is divided into an anterior urogenital triangle that contains the external genitalia and a posterior anal triangle that contains the anus.
As exocrine glands, the ovaries produce ova, and as endocrine glands they produce estrogen and progesterone.
The cortex of the ovary contains ovarian follicles
An egg is an ovum and an immature egg is an oocyte
After the egg is ejected from the follicle, the follicle becomes the corpus luteum
The total number of eggs a woman can produce is determined at birth
Female stem cells called primary divide by mitosis to produce oocytes
It is the very small cell called the polar body that is nonfunctional.
The funnel-shaped opening at the end of each fallopian tube is called the infundibulum
Fertilization takes place in the uterine or fallopian tubes.
The external os is the opening of the cervix into the vagina.
The visceral peritoneum of the uterus is a serous membrane known as the perimetrium
During the menstrual phase, a clear membrane called the zona pellucida develops around the eggs.
The ovum is not released directly into the uterine tube but into the pelvic cavity
The beginning and end of the menstrual cycle in a woman’s life are called, respectively, menarche and menopause.
The recess surrounding the vaginal attachment to the cervix is called the fornix
The mons pubis is also called the veneris
The labia minora of the external genitalia contain numerous sebaceous glands.
The glands homologous to the male Cowper’s glands are the Bartholin’s glands.
Ovulation results from the rupture of the graafian follicle with the subsequent release of a mature ovum.
The paired glands found in the upper pelvic cavity, one on each side of the uterus, are known as the female gonads or ovaries
The formation of the female sex cells, or eggs, occurs in the ovaries and is called oogenesis
The first menstrual period is called menarche
The womb, held in position by a series of ligaments, is located in the pelvic cavity between the rectum and the urinary bladder and is also known as the uterus
The area of the female reproductive system that is homologous to the male scrotum is the labia majora
The thin fold of highly vascularized tissue that partially closes the distal end of the vagina is known as the hymen
The diamond-shaped area at the inferior end of the trunk between the buttocks and thighs of both males and females is known as the perineum
After more tests, Cara and Nicholas decide to try intrauterine insemination (IUI), where Nicholas’ sperm will be placed directly into the uterus. They are told that the procedure needs to be done within 36 hours of ovulation. Cara has a regular 28-day menstrual cycle. On what day of her cycle should ovulation occur? Day 14

Mammary glands are present in both males and females but normally function only in females. Their function is to produce milk to nourish the newborn baby. Estrogen causes the mammary glands to increase in size during puberty. These glands are modified sweat glands and are located in a round skin-covered area called the breast, anterior to the pectoralis major muscle of the thorax.
Each mammary gland consists of 15 to 20 lobes or compartments separated by adipose tissue. It is the amount of adipose tissue present in the breast that determines the size of the breast. In each lobe are several smaller compartments known as lobules, which contain the milk-secreting cells called alveoli (al-VEE-oh-lye). These alveolar glands are arranged in grapelike clusters. They convey the milk into a series of secondary tubules.

From here the milk passes into the mammary ducts. As the mammary ducts approach the nipple, expanded sinuses called ampullae (am-PULL-ah) or lactiferous sinuses (lak-TIF-er-us SIGH-nuh-sez) are found where milk may be stored. These ampullae continue as lactiferous ducts that terminate in the nipple (NIP-l).
The circular pigmented area of skin surrounding the nipple is called the areola (ah-REE-oh-lah). It looks and feels rough because it contains modified sebaceous glands. The function of the mammary glands is to secrete and eject milk, a process known as lactation (lak-TAY-shun).
The size of the breast is determined by the amount of adipose tissue
The circular pigmented area of skin surrounding the nipple of the breast is called the areola
Once the egg cell or ovum ruptures from the ovary in ovulation, it must be fertilized within 12 to 24 hours. Once ejaculated, the sperm cell remains viable within the female reproductive tract for 12 to 48 hours. Some sperm can remain viable for up to 72 hours. For fertilization to occur, sexual intercourse must occur no more than 72 hours before ovulation or no later than 24 hours after ovulation. It takes the ovum 24 hours to go approximately one-third down the uterine or fallopian tube. If fertilization is going to take place, it will occur in the upper two-thirds of the uterine tube.
The sperm cells swim by means of their beating flagella up the vagina and uterus and into the uterine tube. They are attracted to the egg cell by chemicals secreted by the ovum. Although hundreds of sperm cells are surrounding the ovum and rupturing their acrosomes to release enzymes to penetrate the egg cell, only one sperm will penetrate the egg and join its genetic material with the genetic material of the egg to produce a fertilized egg or zygote (ZYE-gote).

As the zygote moves down the uterine tube, it undergoes a series of rapid mitotic divisions, resulting in a hollow ball-like mass of cells called a blastula (BLASS-tyoo-lah) or blastocyst. By the time it reaches the uterine cavity, it consists of about 100 cells. At this stage, part of the blastocyst develops into the chorionic vesicle (KOH-ree-on-ik), and it secretes human chorionic gonadotropin, a hormone, that causes the corpus luteum of the ovary to continue producing its hormones to maintain the lining of the uterus.

By the seventh day following ovulation, the developing embryo has embedded itself in the endometrial lining of the uterus. Meanwhile, the three primary germ layers are being formed by mitotic divisions. The ectoderm will form skin and the nervous system, the endoderm will form the linings of internal organs and glands and the mesoderm will form muscles, bone and the rest of the body tissues. The blastocyst’s inner cell mass forms these primary germ layers and its trophoblast, the large fluid-filled sphere, now begins to form projections called chorionic villi, which will interact with the uterine tissues to form the placenta (plah-SEN-tah).
Once the placenta is formed, the embryo, which looks like a three-layered plate of cells, becomes surrounded by a fluid-filled sac called the amnion (AM-nee-on). The embryo is attached by a connecting stalk of tissue called the umbilical cord. The placenta delivers nutrients and oxygen to and removes wastes and carbon dioxide from the embryonic blood. All exchanges with the mother are made through the placenta. By the ninth week of development, the embryo is now called a fetus.

By the ninth week of development the embryo looks definitely human, the placenta has become an endocrine organ secreting estrogen and progesterone to maintain pregnancy, and the corpus luteum is now inactive. Later on in development, the umbilical cord will become the structure that will allow the exchange of nutrients and wastes between the mother and the fetus.

As pregnancy progresses, the uterus enlarges to accommodate the developing fetus. It eventually pushes up into the abdominal cavity and occupies most of this area. The abdominal organs push against the diaphragm muscle, causing the ribs to expand and the thorax to widen. During this time the center of gravity of the mother moves, resulting in an accentuated curvature of the lumbar vertebrae called lordosis, which may cause backaches. At this time, it is essential for the mother to practice good nutrition, eating high-quality food, not just more food. The mother should also avoid any harmful substances that could pass through the placenta into the fetal blood such as alcohol, drugs and nicotine.
Childbirth is called parturition (par-tyoo-RISH-un). The fetus is expelled from the uterus through a process called labor. The hormone oxytocin causes contraction of the smooth muscles of the uterus. At this time the placenta releases prostaglandins. The combination of these hormones produces more powerful and more frequent contractions of the uterus, forcing the fetus out of the uterus. The stages of labor include the dilation stage, the expulsion stage and the placental stage.

During the dilation stage, the cervix of the uterus is fully dilated by the head of the fetus. The amnion ruptures releasing the amniotic fluid. This is commonly referred to as the water breaking. The dilation stage is the longest stage of labor, lasting up to 12 hours. During the expulsion stage, the child moves through the cervix and vagina to the outside world. This stage usually lasts about 50 minutes in the first birth to about 20 minutes in future births. Usually, the head of the child emerges first, and the nose and mouth are cleared of mucus so the child can breathe.
The umbilical cord is cut and clamped after the rest of the body of the child emerges. A breech birth is one in which the buttocks emerge first and delivery is more difficult. During the placental stage, the placenta detaches from the uterus within 15 minutes after birth. This placenta and its attached fetal membranes are called the afterbirth. The removal of all placental material will prevent prolonged bleeding after delivery.
Human chorionic gonadotropin (HCG) is secreted by the chorionic vesicle
At the ninth week, the embryo is known as a fetus
Parturition is the name given to childbirth.
The amnion is the fluid-filled sac that surrounds the developing embryo/fetus throughout pregnancy.
The embryo is attached to the placenta by a connecting stalk of tissue called the umbilical cord.
By the ninth week of pregnancy, the developing embryo is called a fetus
Happily, the IUI is successful. Nine months later, Cara is having mild contractions, the beginning of labor. What stage of labor is she in now? What stages are to come? How long will each last? She is in the dilation stage. The next two stages will be expulsion and placental. Dilation stage can last up to 12 hours. The expulsion stage is 20 to 50 minutes. The placental stage lasts only a short time and is usually complete by 15 minutes after birth.

Integumentary System 1. Pressure receptors in the skin get stimulated during sexual activity, resulting in sexual pleasure. 2. Male sex hormones activate the skin’s sebaceous glands to produce oil for dermal lubrication. 3. Sex hormones cause the development of pubic and axillary hair during puberty. 4. Female sex hormones cause fat to be deposited on the hips and breasts during puberty. 5. The skin protects the reproductive organs by being the first line of defense against microorganisms.

Skeletal System 1. The bones are a source of calcium needed during lactation, or breastfeeding, of the newborn infant. 2. The pelvis encloses and protects the reproductive organs. 3. The sex hormones cause the development of broad hips in women and narrow hips and broad shoulders in men.

Muscular System 1. The heart pumps blood to maintain an erection. 2. Smooth muscle contractions of the uterus result in delivery of the newborn. 3. Skeletal muscle contractions result in an erection. 4. Male sex hormones cause the development of more muscle mass in men.

Nervous System 1. The nervous system’s sensory and motor neurons play a major role in sexual pleasure and activity. 2. The hypothalamus triggers the onset of puberty. 3. Sex hormones influence the development of the brain in the fetus.

Endocrine System 1. Estrogens and progesterone control the production and development of the ova in females and secondary female sexual characteristics. 2. Testosterone controls the development of sperm and the secondary sexual characteristics of males. 3. Placental hormones maintain pregnancy.

Cardiovascular System 1. Blood pressure maintains erections in both men and women. 2. Blood transports sex hormones to target organs. 3. Pregnancy results in the heart working harder to maintain circulation between the mother and the developing fetus.

Lymphatic System 1. The female immune system does not destroy the male sperm cell, thus ensuring fertilization. 2. The immune system does not reject the developing fetus. 3. The immune system protects the reproductive organs from disease.

Digestive System 1. Proper nutrients are made available to the developing fetus through the mother’s digestive system via the placenta and umbilical cord.

Respiratory System 1. The interaction between the respiratory system and the placenta provides the fetus with oxygen and removes carbon dioxide.

Urinary System 1. The male urethra functions in both the urinary system to transport urine and the reproductive system to transport sperm. 2. The kidneys compensate for fluid loss in the reproductive system. 3. Pregnancy can result in fluid retention, so the kidneys compensate by working harder to eliminate the excess fluid. 4. The developing fetus causes compression of the bladder, resulting in messages to the brain initiating frequent and urgent urination.