Anatomy & Physiology

Anatomy & Physiology Study Guide

23.11 The Rectum The rectum, an expandable organ for the temporary storage of feces, forms the last 6 inches of the digestive tract. By moving fecal material into the rectum, it triggers the bodies need to defecate. The final section of the rectum, the anal canal, contains small longitudinal folds called anal columns . The anus , or anal orifice, is the exit of the anal canal. There, the epidermis becomes keratinized and identical to the surface of the skin. The circular muscle layer of the muscularis externa in this region forms the internal anal sphincter , the smooth muscle cells of which are not under voluntary control. 23.12 Secondary Digestive Organs The Liver The liver is the most massive visceral organ and one of the most skilled organs of the body. Most of its mass lies in the right hypochondriac and epigastric regions, but it may extend into the left hypochondriac and umbilical regions as well. This large, firm organ performs essential metabolic and synthetic functions. It is wrapped in a tight fibrous capsule and covered by a layer of visceral peritoneum. On the anterior surface, the falciform ligament marks the division between the left lobe and the right lobe. A thickening in the posterior margin of the falciform ligament is the round ligament (or ligamentum teres). Round ligaments are a fibrous band that marks the path of the fetal umbilical vein. The impression left by inferior vena cava on the posterior surface of the liver marks the division between the caudate lobe and right lobe. Inferior to the caudate lobe lies the quadrate lobe, sandwiched between the left lobe and the gallbladder. Afferent blood vessels and other structures (i.e., a branch of the portal vein, hepatic artery, and tributary of the bile duct) reach the liver by traveling within the connective tissue of the lesser omentum. They converge at a region called the porta hepatis (“doorway to the liver”). The liver is the principal organ of metabolism. Metabolism has two parts: anabolism (build up) and catabolism (breakdown). The regulatory activities of liver affect the following: carbohydrate metabolism (storing glucose as glycogen through glycogenolysis), lipid metabolism (lipogenesis), amino acid metabolism and protein synthesis, waste product removal, vitamin storage, mineral storage, and drug inactivation. The Bile Duct System Bile, secreted by the liver, flows into a network of slender channels between the opposing membranes of nearby liver cells. These passageways ( bile canaliculi ) extend outward, away from the central vein and eventually connect with the fine bile ductules. These ductules carry bile to bile ducts in the nearest portal area. Hepatic ducts (left and right) then collect the bile from all the bile ducts of the liver loves. These ducts consolidate to form the common hepatic duct, which leaves the liver. The bile in the common hepatic duct either flows into the common bile duct, which empties into the duodenal ampulla or enters the cystic duct, which leads to the gallbladder.

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