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Digestive System

By LarrainedeniseS Sep 28, 2013 5147 Words
THE DIGESTIVE SYSTEM

Functions of the Digestive System
• Ingestion- where in food from outside of the body enters the alimentary tract through the mouth • Digestion- which could be mechanical (physical breakdown of food into smaller pieces or chemical (enzymatic action) • Absorption of digested materials into venous circulation as well as lymphatic capillaries • Provision of nutrients to the cells of the body

• Elimination of undigested materials

ANATOMY AND HISTOLOGY OF THE DIGESTIVE SYSTEM
 The digestive system consists of alimentary tract, or gastrointestinal tract, a tube extending from the mouth to the anus, plus the associated organs, which secrete fluids into the digestive tract.

Main Divisions of the Digestive System

. Digestive Tract (Alimentary Tract)
1. Oral cavity (mouth)​5. Small intestine
2. Pharynx​6. Large intestine
3. Esophagus​7. Rectum
4. Stomach​8. Anus (anal canal)

. Accessory digestive organs
1. Salivary glands
2. Liver and gall bladder
3. Pancreas

Layers or Tunics of the Digestive Tract
1. Mucosa
• the innermost tunic consists of mucous epithelium, a loose connective tissue called the lamina propria, and a thin smooth muscle layer, the muscularis mucosae. 2. Submucosa
• lies outside the mucosa.
• It is a thick layer of loose connective tissue containing nerves, blood vessels, and small glands. An extensive network of nerve cell processes forms a plexus. The plexus is innervated by autonomic nerves. 3. Muscularis

• which in most parts of the digestive tract consists of an inner layer of circular smooth muscle and outer layer of longitudinal smooth muscle. • Another nerve plexus, innervated by autonomic nerves, lies between the two muscle layers. Together the nerve plexuses of submucosa and muscularis compose the enteric nervous system. 4. Serosa or adventitia

• outermost layer of the digestive tract
• The serosa consists of the peritoneum, which is a smooth epithelial layer, and its underlying connective tissue. • Regions of the digestive tract not covered by peritoneum are covered by a connective tissue layer called the adventitia.

THEALIMENTARY OR GASTROINTESTINAL TRACT

1. ORAL CAVITY (MOUTH)
• first part of the digestive tract
• bounded by the lips and cheeks and contains the teeth and tongue
Divisions:
a. Oral vestibule- the space between the teeth internally and lips or cheeks externally b. Oral cavity proper
• Lies internal to the teeth and communicates with oropharynx through oropharyngeal isthmus of fauces • the roof is hard palate composed of palatine process of maxilla and lingual plate of palatine bone o The palate, or the roof of the oral cavity, separates the oral cavity from the nasal cavity and prevents food from passing into the nasal cavity during chewing and swallowing. o The palate consists of 2 parts: the anterior part contains bone and is called the hard palate, whereas the posterior portion consists of skeletal muscle and connective tissue called soft palate. The uvula is a posterior extension of the soft palate • the floor is the tongue

Accessory structures/glands related to the oral cavity

a. Lips
• are muscular structures, formed mostly by the orbicularis oris muscle (striated muscle fibers with fibroelastic connective tissue) o The cheeks form the lateral walls of the oral cavity. The buccinators muscles, located within the cheeks, flatten the cheeks against the teeth. • have an outer surface covered by skin

• the red free margins represent a zone of transition from skin to mucous membrane
b. Cheeks
• side walls of the mouth lined by stratified squamous epithelium, contain several accessory muscles of mastication, notably the buccinators, which prevent food from escaping the chewing actions of the teeth

• The lips and cheeks are important in the process of mastication, or chewing.
c. Teeth
• Two sets of teeth make their appearance during the lifetime of an individual
1. Permanent teeth- 32 teeth in the normal adult located in the mandible and maxillae o The teeth can be divided into quadrants: Right upper, left upper, right lower, and left lower. o In adults, each quadrant contains 8 teeth:

• 1 central incisor, 1 lateral incisor, 1 canine, first and second premolars, and first, second and third molars. (8 teeth per quadrant x 4 quadrants= 32 teeth) o The third molars are called wisdom teeth because they usually appear in the late teens or early twenties, when the person is old enough to have acquired some degree of wisdom. • Eruption of the third molar is delayed after the age of 18, and one or more are absent in up to 25 percent of populations

2. Deciduous teeth (otherwise known as milk teeth or temporary teeth) • 20 teeth in children- which are lost during childhood
• Each quadrant contains 5 teeth:
• 1 central incisor, 1 lateral incisor, 1 canine, and first and second molars (5 per quadrant x 4 quadrants= 20) • erupt on the average between 6 and 24 months after birth and are usually shed between the ages 6 and 12

d. Tongue
• a large, muscular organ that occupies most of the oral cavity • The major attachment of the tongue is in the posterior part of the oral cavity. The anterior part of the tongue is relatively free, except for an anterior attachment to the floor of the mouth by a thin fold of tissue called the frenulum. • Parts: root, apex, and body

• Surfaces:
a. Inferior
• mucous membrane continuous with that of the gums and floor or mouth • frenulum linguae at the midline
• presents sublingual papillae at inferior end of lingual frenulum, where Wharton’s and Bartholin’s duct open • lateral to sublingual papillae is the sublingual fold while underneath is the sublingual gland • at the summit of the sublingual gland are the openings of ducts of Rivinus b. Dorsal

• convex median sulcus divides tongue into lateral halves and ends posteriorly in foramen cecum
Features of the dorsum of the tongue:
• Papillae- enlargements on the surface of the tongue
o Taste buds- oval structures located on the surface of certain papillae; sensory receptors for taste Each taste bud is composed of two types of cells:
a. gustatory (taste) cells- the interior part of the taste buds which contains hairlike processes called taste hairs, which extend into a tiny opening in the surrounding stratified epithelium, called a taste pore. b. supporting cells- specialized epithelial cells that form the exterior supporting capsule of each taste bud and encapsulate the taste cells

Types of papillae
1. circumvallate papillae- largest papillae; with taste buds 2. fungiform papillae- with taste buds
3. foliate papillae- with taste buds
4. filiform papillae-no taste buds; only gustatory cells

Functions of the tongue:
o The tongue moves food in the mouth, and in cooperation with the lips and cheeks, holds the food in place during the process of mastication. o It also plays a major role in the process of swallowing (deglutition) o A major sensory organs for taste, as well as one of the major organs for speech • Agustia- absence of taste

Nerves of the tongue
1. General Sensory (pain, pressure, etc)
• Lingual branch of CN V– anterior 2/3 of tongue
• Glossopharyngeal (CN IX)- posterior 1/3 of tongue
• Vagus (CN X)- epiglottic area
2. Special Sensory (sense of taste)
• Facial (CN VII)- anterior 2/3 of tongue
• Glossopharyngeal (CN IX)- posterior 1/3 of tongue
3. Motor
• Hypoglossal (CN XII)- to intrinsic and extrinsic muscles of the tongue

e. Tonsils (Just located in the oral cavity but Part of Lymphatic System) • are located in the lateral posterior walls of the oral cavity, in the nasopharynx, and in the posterior surface of the tongue • form a protective ring of lymphatic tissue around the openings between the nasal and oral cavities and the pharynx, called the “Waldeyer’s Ring” • protect against pathogens and other potentially harmful material entering from the nose and mouth • Three groups of tonsils:

1. Palatine tonsils
o located on each side of the posterior opening of the oral cavity o the largest and most often infected
o these are the ones usually referred as “the tonsils”
2. Pharyngeal tonsils
o located near the internal opening of the nasal cavity
o When the pharyngeal tonsil is enlarged, it is commonly called the adenoid, or adenoids 3. Lingual tonsil- located on the posterior surface of the tongue
f. Salivary glands (to be discussed in the Accessory Digestive Organs)

2. PHARYNX
• or throat, connects the mouth with the esophagus, consists of three parts: the nasopharynx, oropharynx, and the laryngopharynx. (as discussed in The Respiratory System) • Normally, only the oropharynx and laryngopharynx transmit food o Therefore only the oropharynx and laryngopharynx are parts of the digestive system • No digestion takes place

3. ESOPHAGUS
• a muscular tube, lined with moist stratified squamous epithelium, that extends from the pharynx to the stomach • about 25 cm (10 inches) long and lies anterior to the vertebrae and posterior to the trachea within the mediastinum • it passes through the diaphragm in front of the aorta and ends at the stomach • Parts/Segments of the esophagus:

a. Cervical portion- located behind the trachea; at the level of C6 b. Thoracic portion- the longest; Upper portion: at the level of the Angle of Louis and the lower portion: at the level of T10 Anatomical relations are:

o Anterior- trachea; pericardium and heart
o Posterior- vertebral column
c. Abdominal portion- shortest and passes thru the esophageal orifice of diaphragm at the level of T10 to open into the stomach; anteriorly it is covered by the liver and posteriorly rests on the diaphragm • Upper and lower esophageal sphincters, located at the upper and lower ends of the esophagus, respectively, regulate the movement of food into and out of the esophagus. o The lower esophageal sphincter is sometimes called the cardiac sphincter. • Function: transports food from the pharynx to the stomach

4. STOMACH
• the most dilated portion of the digestive tract found between the esophagus and the small intestine with a capacity o f about 1.5 liters in adults • lies under the diaphragm; in the left upper quadrant, in the left hypochondriac, epigastric and umbilical regions of the abdomen • position and shape depend upon its contents and position o f the body as well as phase of respiration • Function: temporary storage of food and a mixing chamber for ingested food prior to passage to duodenum (the first part of the small intestine), but some digestion takes place and the mixed partially digested food is reduced to semifluid mass • Three major parts of the stomach:

a. Fundus
• the most superior part of the stomach; the expanded region lateral to the cardiac region • upper portion ballooning at the left
• the part of the stomach above the imaginary line drawn from cardiac orifice to greater curvature o Cardiac orifice (opening)- opening from the esophagus into the stomach ( so called because it is near the heart) o Cardiac region- region of the stomach around the cardiac opening b. Body- the largest part of the stomach, which turns to the right, forming: o Greater curvature- on the left side; convex lateral border continuous with esophagus at the cardiac notch o Lesser curvature- on the right side; concave medial border continuous with the right border of the esophagus c. Pylorus (antrum)

• the terminal part continuous with the small intestine through the pyloric sphincter o Pyloric orifice (opening)- opening from the stomach into the duodenum of small intestine, which is surrounded by a relatively thick ring of smooth muscle called the pyloric sphincter. o Thick circular muscle in pyloric portion forms the pyloric sphincter o Pyloric region- the region of the stomach near the pyloric orifice • The muscular layer of the stomach is different from other regions of the digestive tract in that it consists of 3 layers: outer longitudinal, a middle circular, and an inner oblique layer. • The submucosa and mucosa of the stomach are thrown into large folds called rugae. • The stomach is lined with simple columnar epithelium

• The mucosal surface forms numerous tubelike gastric pits, which are openings for the gastric glands.
• Cells of the gastric glands:
o mucous neck cells- produce mucus, which lubricates and protects the epithelial cells of the stomach wall from the damaging effect of the acidic chyme and pepsin. o parietal cells- produce hydrochloric acid (HCl) and intrinsic factor • The hydrochloric acid produces a pH of about 2 in the stomach, kills microorganisms and activates pepsin from the inactive form called pepsinogen. • The intrinsic factor binds with vitamin B12 and makes it more readily absorbed in the small intestine. o chief cells- produce pepsinogen, a precursor of the protein-digesting enzyme pepsin • Pepsin breaks covalent bonds of proteins to form smaller peptide chains. o G cell- secrete gastrin

RELATIONS OF THE STOMACH
a. Anterior surface
• covered partly by the left lobe of the liver.
• the fundus is partly overlapped by spleen
• diaphragm separates the stomach from the left lung and heart • related with the anterior abdominal wall below the costal margin
b. Posterior surface
• lesser sac (omental bursa) is found at the back of stomach which lies on structures mainly retroperitoneal ones on the posterior wall of this sac • The structures forming the stomach bed are as follows:

o pancreas with splenic artery on its superior border
o diaphragm
o left kidney
o left suprarenal gland
o spleen
o transverse colon

5. SMALL INTESTINES
• about 6 m long and consists of three parts: the duodenum, jejunum and ileum • the longest part of the digestive tract
• Function/s of the small intestine: the major site of digestion and absorption of food, which are accomplished due to the presence of a large surface area. • It is in the small intestines where final digestion of food and major absorption of ingested food happen • Parts of the small intestine:

a. Duodenum
• the C-shaped first portion of the small intestines about 25 cm (10 inches) long • shortest, widest, most fixed and thickest of the small intestine • almost retroperitoneal except the 1>1 inch of the lst portion • begins at the pylorus and ends to the left midline opposite the lumbar vertebra in the jejunum • the common bile duct from the liver and the pancreatic duct from the pancreas join and empty into the duodenum • together with the pancreas it is most deeply lying portion of the alimentary tract • Functions of duodenum:

a. secretions: secretin and pancreozymin
b. receives bile and pancreatic juice through the common bile duct and pancreatic ducts

• Divisions of duodenum:
1. superior - 1st portion
• also called duodenal bulb or duodenal cap (triangular shadow on X-ray) • begins at the pylorus, ends at the level of neck of gall bladder 2. descending - 2nd portion
• extends from the level o f the neck of the gallbladder (LI vertebra) along the right side of vertebral column to as low as the L4 vertebra • receives the opening of common bile duct and pancreatic ducts (main pancreatic duct of Wirsung and accessory pancreatic duct of Santorini)

3. transverse/horizontal - 3rd portion​
• begins at the right side of the upper border of L4 vertebra • crosses the midline in front of the inferior vena cava and crura of the diaphragm, ends in the ascending portion in front of abdominal aorta

4. ascending – 4th portion
• ascends on the left side of aorta up to the level of L2 vertebra • ends at the duodenojejunal flexure, where it joins with the jejunum
b. Jejunum
• about 2.5 m long and makes up the 2/5 of the total length of the small intestine • the junction o f the duodenum with the jejunum is marked by a flexure and/or the ligament of Treitz that is attached to the posterior abdominal wall • the duodenojejunal flexure marks the junction between upper gastrointestinal tract and lower gastrointestinal tract

c. Ileum
• about 3.5 m long and makes up the 3/5 of the total length of the small intestine • The site where ileum connects to the large intestine is called the ileocecal junction. It has a ring of smooth muscle, the ileocecal sphincter, and an ileocecal valve, which allow the intestinal contents to move from the ileum to the large intestine, but not in opposite direction.

• Both the jejunum and ileum are completely surrounded by peritoneum hence they possess a mesentery, mesentery proper • There is no morphological line of demarcation between jejunum and ileum.
Functions of the jejunum and ileum: specialized for the absorption of digested foodstuff, vitamin and electrolytes.

Three structural modifications in the small intestines that increase its absorptive area a. circular folds (plicae circularis/ valves of Kerkring) – deep folds of mucosa and submuscosa that run perpendicular to the long axis of the digestive tract b. villi- fingerlike projections of the mucosa that gives the small intestine a velvety appearance and texture. o Most of the cells composing the surface of the villi have numerous cytopasmic extensions called microvilli. o Each villus is covered with simple columnar epithelium. Within the loose connective core of each villus are a blood capillary network and a lymphatic capillary called a lacteal. c. microvilli- minute projections of the surface plasma membrane of the cells in the lining epithelium

• Peyer’s patches- large collection of lymphatic nodules found numerous on the ileum. These lymphatic tissues help protect the intestinal tract from harmful microorganisms.
6. LARGE INTESTINES
• From cecum to sigmoid colon
• Functions:
 compact and propel the fecal matter towards the anal canal and eliminate it in the anus  absorption of the remaining water and some electrolytes in the undigested food  The bacterial flora in the large intestine provides the body with vitamin K.

• Parts of the large intestine

1. Cecum
• the proximal end of the large intestine where it joins with the small intestine at the ileocecal junction • located in the right lower quadrant of the abdomen near the ileac fossa • it is a sac that extends inferiorly past the ileocecal junction • has an average length of 6 cm and about 7.5 cm wide

• with no mesentery; covered on all sides with peritoneum. • Cecum however is commonly mobile and may even herniate through the right inguinal canal • Communications:
o Superiorly - with the ascending colon
o Posteromedially - vermiform appendix
o Left side – ileum

2. Vermiform appendix
• Attached to the posteromedial aspect of the cecum 2 cm inferior to the ileocecal opening • has a variable length, and it could be as long as 20 cm
• the attachment of the base o f the appendix to the cecum is quite constant, coinciding with the commencement of the taenia coli
3. Colon
• about 1.5-1.8 m (5ft) long and consists of four parts: the ascending colon, the transverse colon, the descending colon, and the sigmoid colon
a. Ascending colon
• extends superiorly from the cecum to the right colic flexure, near the liver, where it turns to the left o begins at the upper border of the ileocecal junction and ends just below the liver o bends to the left in front of the right kidney(right colic or hepatic flexure) • covered with peritoneum only in front and sides, hence it is fixed to posterior abdominal wall

b. Transverse colon-
• extends from the right colic flexure to the left colic flexure near the spleen, where the colon turns inferiorly o begins at the right colic flexure and runs across in front of coils of small intestine to the left side o It ends in left colic flexure (splenic flexure)

• completely invested by peritoneum, and possesses a mesentery, the transverse mesocolon attaching it to the anterior surface ofthe pancreas (posterior abdominal wall)
c. Descending colon
• extends from the left colic flexure to the pelvis, where it becomes the sigmoid colon o begins at the left colic flexure passes downward through the hypochondriac and lumbar regions along the lateral border of the left kidney o continuous with sigmoid colon at the pelvic brim (inlet)

• Like the ascending colon, descending colon is covered by peritoneum only at the front and sides, hence not movable d. Sigmoid colon-
• forms an S-shaped tube that extends medially and then inferiorly into the pelvic cavity and ends at the rectum • begins at the level of the pelvic inlet where it is continuous proximally with descending colon • The average length is about 40 cm. and normally lies within the pelvis. • - It is completely surrounded by peritoneum, which form a mesentery, the sigmoid mesocolon

Peculiar characteristics of the cecum and colon
1. Taenia coli
• are 3 narrow ribbon-like bands made up of the longitudinal muscle of the cecum and colon • They are shorter than the colon, thereby causing a puckering or sacculations or haustra • their commencement is at the base of the appendix

2. Haustra coli or sacculations- involve the circular muscle, submucosa and mucosa. 3. Appendices epiploecae
• are small fatty tags that project from the serous coat of large intestine • Most of them are attached to the colon between its internal margin and the anterior taenia • They appear in 2 rows in the pelvic region, one on each side of the anterior taenia • In the appendix, cecum and rectum they contain little fat or maybe absent

• The mucosal lining of the colon contains numerous straight, tubular glands called crypts, which contain many mucus-producing goblet cells. • The longitudinal smooth muscle layer of the colon does not completely envelop the intestinal wall but forms three bands called teniae coli.

1. RECTUM
• a straight, muscular tube that begins at the termination of the sigmoid colon and ends at the anal canal • the muscular tunic is composed of smooth muscle and is relatively thick in the rectum compared to the rest of the digestive tract.

2. ANAL CANAL (ANUS)
• the last 2-3 cm of the digestive tract
• begins at the inferior end of the rectum and ends at the anus (external digestive tract opening) • The smooth layer of the anal canal is even thicker than that of the rectum and forms the internal anal sphincter at its superior end. The external anal sphincter at the inferior end of the anal canal is formed by skeletal muscle. • Hemorrhoids- are enlarged or inflamed rectal, or hemorrhoidal, veins that supply the anal canal.

Note: The sigmoid, rectum, and anal canal are found in the pelvic cavity
ACCESSORY DIGESTIVE ORGANS (Salivary glands, Liver and gall bladder, and Pancreas)
1. SALIVARY GLANDS
• glands that produce saliva
• secretions (salivary amylase) poured in the oral cavity start the digestion of carbohydrates • Three types of salivary glands:
a. Parotid glands
• the largest of the salivary glands are serous glands located just anterior to each ear • lies in the posterior border of ramus of mandible
• Important structure embedded: facial nerve
• Mumps is the inflammation and swelling of the parotid gland caused by a virus. b. Submandibular glands
• second largest salivary glands
• located halfway along the body of the mandible, medial to its margin, just deep to the mylohyoid muscle • can be felt as a soft lump along the inferior border of the mandible c. Sublingual glands

• smallest of the 3 paired salivary glands
• lie immediately below the mucous membrane in the floor of the oral cavity

SALIVARY GLANDS
TYPE OF SECRETION
NAME OF DUCT
Parotid gland
Purely serous (watery)
Stensen’s duct - passes superficially over the masseter, pierces the buccinator, and opens into the vestibule of the mouth opposite the second upper molar tooth Submandibular gland
Mixed mucoserous; predominantly serous
Wharton’s duct- opens into the oral cavity on each side of the frenulum of the tongue near the lower central incisors. Sublingual
Mixed mucoserous; predominantly mucous
Bartholin’s duct- opens onto the floor of the oral cavity posterior to the papilla of the submandibular duct

SALIVA
o Saliva helps keep the oral cavity moist and contains enzymes that begin the process of digestion. The serous part of the saliva, produced mainly by parotid and submandibular glands contains a digestive enzyme called salivary amylase, which breaks the covalent bonds between glucose molecules in starch and other polysaccharides. o Saliva also prevents bacterial infection in the mouth by washing the oral cavity, and it contains lysozyme, a enzyme that has a weak antibacterial action. o The serous part of the saliva dissolves molecules, which must be in solution to stimulate taste receptors. The mucous secretions of the submandibular and sublingual glands contain a large amount of mucin, a proteoglycan that gives a lubricating quality to the secretions of the salivary glands.

2. LIVER
• the largest gland in the body located in the right upper quadrant (right hypochondriac region extending to epigastric region) • occupies the uppermost part of the abdomen, covered by the lower ribs that afford some protection • extremely vascular (reddish-brown in color)

• its shape resembles a pyramid, the base on the right and the apex on the left • In males, generally weighs 1.4-1.8 kg and in female, 1.2-1.4 kg, with a range of 1-2.5 kg. • located in the right upper quadrant of the abdomen, tucked against the inferior surface of the diaphragm


LOBES OF THE LIVER
1. Right and left lobes (major lobes)
• contributes to all surfaces, including the entire surface covered by the ribs • Its surfaces (anterior, superior, inferior and posterior) all pass uninterruptedly onto the left lobe, except where shallow grooves partially demarcate the quadrate and caudate lobes • separated by a connective tissue septum, the falciform ligament 2. Quadrate lobe

• visible on the inferior surface
• somewhat rectangular and is bounded in front by the inferior border and behind by the porta hepatis, on the left is the fissure for the ligamentum teres, on the right by the fossa for the gallbladder 3. Caudate lobe

• visible on the posterior surface
• bounded on the left by the fissure for the ligamentum venosum, below by the porta hepatis, and on the right by the groove for the inferior vena cava • below and to the right it is connected by a narrow process, the caudate process, to the right lobe

 Anatomically, the liver is divided into right and left lobe by means of falciform ligament, a peritoneal reflection  But functionally, the real landmark dividing the right and left lobes is the line passing through the fossa for inferior vena cava and gall bladder. Hence, quadrate and caudate lobe will be parts of the left lobe.  Also seen from the inferior view of the liver is the porta (porta hepatis), which is the “gate” through which blood vessels, ducts, and nerves enter or exit the liver  receives blood from two sources:

o hepatic artery- takes oxygen-rich blood to the liver, which supplies liver cells with oxygen o hepatic portal vein- carries blood that is oxygen-poor but rich in absorbed nutrients and other substances from the digestive tract to the liver  Many delicate connective tissue septa divide the liver into lobules with portal triads at their corners. The portal triads contain three structures: hepatic artery, hepatic portal vein and hepatic duct (duct of the liver) • The liver secretes 700 ml of bile each day.

o Bile contains no digestive enzymes, but it plays an important role in digestion by diluting and neutralizing stomach acid and by dramatically increasing the efficiency of fat digestion and absorption. o Bile salts emulsify fats, breaking fat globules into smaller droplets, much like the action of detergents in dishwater. o Bile also contains excretory products, such as cholesterol, fats and bile pigments, including bilirubin, a bile pigment that results from the breakdown of hemoglobin.

Functions of the Liver
Function
Explanation
Digestion
Bile neutralizes stomach acids and emulsifies fats, which facilitates fat digestion Excretion
Bile contains excretory products, such as cholesterol, fats, and bile pigments (e.g. bilirubin), that result from hemoglobin breakdown Nutrient storage
Liver cells remove sugar from the blood and store it in the form of glycogen; they also store fat, fat-soluble vitamins (A, D, E, and K), copper and iron Nutrient conversion
Liver cells convert some nutrient into others; for example, amino acids can be converted to lipids or glucose, fats can be converted to phospholipids, and vitamin D to its active form Detoxification of harmful chemicals

Liver cells remove ammonia from the circulation and convert it to urea, which is eliminated in the urine, other substances are detoxified and secreted in the bile or excreted in the urine Synthesis of new molecules

The liver synthesizes blood proteins, such as albumin, fibrinogen, globulins, and clotting factors

EXTRAHEPATIC BILIARY SYSTEM
Components:
1. Common hepatic duct
2. Gall bladder and cystic duct
3. Common bile duct

 The right and left hepatic ducts of the liver unite to form a single common hepatic duct. The common hepatic duct is joined by the cystic duct (duct of the gall bladder) to form common bile duct.  The common bile duct joins the pancreatic duct and opens into the duodenum at the duodenal papillae (an elevation of the duodenal mucosa)

Gall bladder
• is an elongated pear-shaped sac on the inferior surface of the liver that stores and concentrates bile • its non-peritoneal surface is attached to the liver by connective tissue between the right lobe and quadrate lobe • Parts of the gall bladder:

a. Fundus
• the expanded blind anterior end of the organ that projects beyond the inferior margin o f the liver • this part of the gallbladder is completely covered with peritoneum and is in contact with the anterior abdominal wall just below the tip o f the 9th right costal cartilage • Phrygian cap is a notched or kinked fundus of the gallbladder b. Body

• the main part of the gallbladder
• tapers toward its neck
• covered with peritoneum at the sides and inferiorly
• its inferior surface is in contact with related to 2nd part o f the duodenum and to transverse colon c. Neck
• the superior constricted portion o f the gallbladder that is proximal to the cystic duct
3. PANCREAS
• a long flat pistol shaped gland, the head part of which is enclosed by the duodenum and the main parts posterior to the stomach • located retroperitoneal, posterior to the stomach in the inferior part of the left upper quadrant • Parts of the pancreas:

b. Head
• broad and flat, enclosed by the curve of the duodenum
• to the left and upper part, continuous with the neck
• to the left and lower part, projects the uncinate process c. Neck- is constricted by the superior mesenteric vessels which lie in a deep groove o f the posterior surface and the neck d. Body- lies above the duodenal flexure and lies behind the stomach e. Tail- the tapering left extremity extending into the lienorenal ligament and to the hilus of the spleen RELATIONS:

Anterior surface
• transverse mesocolon across the head and lower part o f the neck and body • the stomach is found anteriorly
o Above, the lesser curvature, the lesser omentum and through it the liver, and the 1st part o f the duodenum Posterior surface
• the head lies on the hilum of the right kidney
• the neck and uncinate process lie in front of abdominal aorta • the body crosses the left kidney and suprarenal gland and the right crus of the diaphragm
Two pancreatic ducts
a. Main or chief pancreatic duct or duct of Wirsung
• runs the length of the pancreas from the entire tail and body and from the postero-inferior part of the head, including uncinate process • ends by opening into the 2nd portion o f the duodenum
• In 2/3 o f the cases, however, joins with the common bile duct to form a dilatation called AMPULLA OF VATER which opens in the descending portion of the duodenum. o This opening is guarded by smooth muscle called SPHINCTER OF ODDI and found in an elevation in the duodenal mucosa called MAJOR DUODENAL PAPILLA.

b. Accessory pancreatic duct of Santorini
• if present drains the antero-superior part o f the head only and empties independently into the 2nd part of the duodenum, at the minor duodenal papilla just above the major duodenal papilla.

• Functions of the Pancreas: (with endocrine and exocrine functions)

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