Structure Of Human Body Systems

Structure of Main Body Systems
How The Human Body Works
The Su Yi Win
Health & Social Care (Foundation)
Victoria University College

Main Body Systems
• A human body system consists of specific cells, tissues and organs that work together to perform specific functions. These systems work together to maintain your overall health. Some of the body systems are as below :

Cardiovascular System
• Consists of the Heart, Blood Vessels (Veins, Arteries, Capillaries) and Blood. Its main function is to allow blood to circulate and transport nutreints and oxygen to and from body cells.
• The Heart is a muscular pumping organ located medial to the lungs along the body’s midline in the thoracic region.
• Blood vessels are lined with a thin layer of simple squamous epithelium that keeps the blood cells inside the vessels and prevents clots from forming.
• Arteries carry blood away from the heart to the lungs to be oxygenated. • Veins return de-oxygenated blood from the tissues back to the heart for re-oxygenation.
• Capillaries are the smallest and thinnest blood vessels. They run through almost every tissue of the body to transport oxygenated blood from the arteries and carry back waste products from the veins. • Arteries have the thickest and most elastic walls so that they can withstand oxygenated blood with high pressure from the heart’s contractions.
• Veins have thinner walls and many have one-way valves to prevent blood flowing away from the heart.
• Blood is made up of red blood cells, white blood cells, platelets and plasma.
• Red blood cells contain the red pigment haemoglobin, that is composed of irons and proteins.
Oxygen
is carried by haemoglobin to form oxyhaemoglobin and thus oxygenated blood.

Respiratory System
• The respiratory system is composed of the lungs, heart and blood vessels. Its main function is to deliver oxygen to the body’s blood and take away carbon dioxide.
• The lungs are a pair of spongy, air-filled organs located on either side of the throax. The trachea transports inhaled air into the lungs through bronchi. These bronchi branch into smaller bronchioles (microscopic) that leads to small, spongy sacs called alveoli, where gaseous exchange occurs.
• Alveolar walls are extremely thin and is composed of a single layer of tissues and tiny blood vessels called pulmonary capillaries. • Capillaries carry oxygenated blood from the heart to the alveoli.
• Human cells & tissue require oxygen to function properly and release carbon dioxide as waste products.

• Inhaled air is rich in oxygen which the alveoli is full of. Oxygen moves by diffusion across the alveolar walls to the blood in the capillaries.
• The capillaries also contains carbon dioxide and other waste products carried back from the body cells (de-oxygenated blood). • The red blood cells in the blood carry the fresh oxygen and nutrients from inhaled air, and release the carbon dioxide and waste products back into the lungs for exhalation

Digestive System
• Group of organs working together to convert food into energy and nutrients for the entire body.
• The gastrointestinal tract is made up of the oral cavity, esophagus, stomach, liver, pancreas, small intestine and large intestine. • Food is first ingested by the mouth, where teeth chop food into small pieces and is moistened by saliva. Saliva contains the enzyme amylase which acts on the food and digests starch
(carbohydrates) into simple sugars of maltose.
• The esophagus is a muscular tube, extending from the throat to the stomach. By a series of muscle contractions, peristalsis, the esophagus delivers food into the stomach. At the end of the esophagus is a muscular ring called the esophageal sphincter that closes the end of the esophagus and trap food in the stomach.

• The stomach is a muscular sac at the left side of the thorax. It produces gastric acid, which contains mainly hydrochloric acid and digestive enzymes (lipase).
• Hydrochloric acid kills any bacteria and harmful micro-organisms in the food. The stomach churns the food until it becomes pastelike (chyme). It then releases the food into the first part of the small intestine, the duodenum.
• Liver is an accessory digestive gland, triangular in shape and located right of the stomach, that produces bile, an important alkaline compound. Bile emulsifies fatsin the chyme and breaks down lipids into smaller droplets, to create a larger surface area for enzymes to work on later. Bile is transported to the duodenum via the bile duct.
• Pancreas, a large gland posterior to the stomach, produces pancreatic juice containing many digestive enzymes (lipase, protease, maltase). The digestive juice is transported to the duodenum via the pancreatic duct.

• In the duodenum, pancreatic juice and bile continue the digestion of chyme. Proteins are broken down into amino acids by the enzyme protease. Lipids are emulsified into smaller droplets by bile, then further digested into fatty acids by lipase enzymes. Maltose sugars are further digested into simpler sugar, glucose, by the enzyme maltase.
• The digested chyme now travels into the lower small intestine, the jejunum and ileum. They have villi on their surface, and so digested nutrients are absorbed into the bloodstream.
• The food is now transported down into the large intestine
(colon). The colon further absorbs remaining moisture and nutrients, before the rest is expelled as faeces through the anus. Renal System
• Consists of two kidneys, ureters, the bladder and urethra.
• Main purpose is to eliminate wastes from the body, regulate blood volume and pressure, control electrolyte levels and regulate blood pH.
• Kidneys are bean shaped and found along the posterior wall of the abdominal cavity. They filter wastes, excess ions and chemicals from the blood to form urine.
• The ureters are a pair of tubes (10-12inches long) that carry urine from the kidneys to the bladder.
• The bladder is a sac-like hollow organ that stories urine.
• The urethra is a tube where urine is excreted from the bladder to the exterior of the body.

• The basic structure of the kidney is the nephron. Arteries in the kidneys deliver blood to a bundle of capillaries in the kidneys, called a glomerulus. As blood flows through the glomerulus, the blood’s plasma is pushed out of the capillaries into the it while the blood cells and a small amount of plasma continue to flow through the capillaries.
• The filtrate flows through many more capillaries across many tubules that selectively absorb water and substances, while returning the blood into the capillaries.
• The waste products in the blood are secreted into the filtrate.
• At the end of the process, the filtrate has become urine, waste products and excess ions.

• The urine is then transported through the ureters to the bladder. The bladder stores it until the body is ready for release. The muscle of the urethral sphincters relax, allowing the urine to pass through the urethra.

Nervous System
• It is divided into two parts, Central Nervous
System (CNS) and
Peripheral
Nervous
System (PNS).
• CNS consists of the brain and spinal cord.
• PNS consists mainly of nerves. • The system controls the body’s voluntary and involuntary actions and transmits signals to all body parts.

• A neuron is the basic building block of a cell.
• Sensory neurons carry information from the sensory receptor cells throughout the body to the brain. Motor neurons transmit information from the brain to the muscles of the body.
Interneurons are responsible for communicating information between different neurons in the body.
• In order for neurons to communicate, they need to transmit information both within the neuron and from one neuron to the next. This process utilizes both electrical signals as well as chemical messengers. The dendrites of neurons receive information from sensory receptors or other neurons. This information is then passed down to the cell body and on to the axon. Once the information as arrived at the axon, it travels down the length of the axon in the form of an electrical signal known as an action potential.

• When the action potential reaches the axon ending, it causes tiny bubbles of chemicals called vesicles to release their contents into the synaptic gap. These chemicals are called neurotransmitters. These sail across the gap to the next neuron, where they find special places on the cell membrane of the next neuron called receptor sites.

Endocrine System
• Collection of various glands that produces hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep and mood etc. • Major glands include pituitary gland, thyroid gland, pancreas, ovary, testis, adrenal gland and thymus gland.
• The system’s effects are slow to initiate but the effect is prolonged. All the glands are ductless. • Pituitary gland is located at the bottom of the brain. Produces growth hormone, puberty hormones and thyroid stimulating hormone (TSH, stimulates thyroid to make Thyroxine).
• Thyroid gland is found in the neck, and produces Thyroxine, that controls the body’s growth.
• Pancreas is located in the abdominal cavity behind the stomach, which produces digestive juices.
• Adrenal glands are found on top of the kidneys that produces steroid hormones and the hormone adrenaline – that prepares your body to spring into action in a stressful situation
• Ovary is part of the female reproductive system, which produces the female hormones progesterone and oestrogen. Testis is part of the male reproductive system, which produces male hormone testosterone. Reproductive System
• System of sexual organs that work together for sexual reproduction, produce offspring.
• Female reproductive system consists of the uterus, fallopian tube, ovary, cervix and vagina.
• Male reproductive system consists of the prostate gland, seminal vesicle, penis, urethra and testis.

• The human system involves internal fertilization by sexual intercourse. • The male will insert his erect penis into the female’s vagina and ejaculate semen, which contains sperm.
• The sperm will travel through the vagina and cervix into the uterus or fallopian tubes for fertilization of the ovum.
• Upon successful fertilization and implantation, the fetus then grows for approximately nine months before labor occurs.
• Sperm production takes place in the testis in males. Seminal vesicles produce ejaculatory fluid and upon ejaculation, travels through the urethra to be ejaculated via the penis.
• Approximately every 28days, the ovary produces a single ovum which waits to be fertilized inside the fallopian tube.

Lymphatic System
• The lymphatic system is a system of thin tubes and lymph nodes that run throughout the body.
• These tubes are called lymph vessels or lymphatic vessels.
The lymph system is an important part of our immune system.

• The intercellular fluid slowly begins to accumulate and must be returned to the cells and the blood stream. Enter the lymph system. The lymph system gathers those fluids and returns them to your blood. The lymph system is also closely associated with your immune system and swelling of tissues after an injury.
• Lymph nodes are often found in your thighs, armpits, and neck. The nodes are actually accumulations of lymph tissue.
They are great filters of foreign. Bacteria and cancer cells often enter the lymph system and intercellular fluids are collected. • Not only do nodes remove cells, they also create cells called lymphocytes. Those lymphocytes are white blood cells used by the immune system to produce antibodies (phagocytosis).

Musculo-Skeletal System
• The human musculoskeletal system is an organ system that controls human’s ability to move, provides form, support and stablity.
• It is made up of the bones of the skeleton, muscles, cartilage, tendons, ligaments, joints and other connective tissue that supports and binds tissues and organs.

Immune System
• The immune system is a system of biological structures and processes within an organism that protects against disease.
To function properly, an immune system must detect a wide variety of agents, known as pathogens, from viruses to parasitic worms, and distinguish them from the organism's own healthy tissue.
• Consists of white blood cells (lymphocytes).
• Two types of lymphocytes, B cells and T cells.