Digestive System Part IV: Small & Large Intestines
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| Small intestine | organ in which most chemical digestion and most absorption occur; extends from pyloric region of stomach to cecum of large intestine; longest organ of digestive tract; subdivisions are duodenum, jejunum, ileum
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| Duodenum | subdivision of small intestine; extends from pyloric sphincter to constitute about the first 10 inches of small intestine; receives enzymes from pancreas via pancreatic duct, receives bile from liver & gallbladder via common bile duct
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| Jejunum | middle portion of small intestine; makes up superior left coils of small intestine
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| Ileum | terminal (distal) and longest portion of small intestine; makes up inferior right coils of small intestine; joined to cecum of large intestine at ileocecal valve
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| Ileocecal valve | located at junction of ileum of small intesting and cecum of large intestine; controls movement of food residue from small intestine to large intestine
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| Hepatopancreatic ampulla | bulb formed by pancreatic duct and bile duct where they enter wall of duodenum; opens into duodenal lumen via major duodenal papilla
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| Circular folds/plicae circularis, villi, microvilli | structural features of small intestine that greatly increase its surface area and thus account for small intestine’s extensive absorptive capacity
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| Circular folds/Plicae circulares | circular wrinkles in small intestine lining; increase surface area for absorption
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| Villi | about 1mm high; finger-like projections of small intestine mucosa; give it velvety appearance/feel; covered w/ layer of simple columnar epithelium; core is made of lamina propria; each contains network of blood capillaries and lymphatic capillary/lacteal
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| Microvilli | tiny, microscopic, bristle-like projections of upper surface of mucosal epithelial cells; significantly amplify surface area of epithelial cells, thus enhancing nutrient absorption
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| Goblet cells | in lining epithelium of small intestine; secrete a coating of mucus onto internal surface of both small and large intestine
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| Enteroendocrine cells of duodenum | cells in lining epithelium of small intestine; secrete hormones including cholecystokinin, which stimulates gallbladder to release stored bile
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| Cholecystokinin | hormone secreted by enteroendocrine cells of duocenum; stimulates gallbladder to release stored bile
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| Intestinal glands/intestinal crypts/crypts of Lieberkuhn | indentations of cells in mucosa between villi; epithelial cells in these indentations secrete intestinal juice and renew mucosal epithelium by undergoing rapid mitosis and moving continuously into the villi
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| Aggregated lymphoid nodules/Peyer’s patches in ileum | lymphoid tissue in lamina propria and submucosa of small & large intestine; keeps large numbers of bacteria in the lumen of small and large intestines from getting out of hand.
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| Intestinal flora | normal permanent bacterial residents of intestinal lumen of both small and large intestines; produce some essential vitamins including vitamin K and some B vitamins which the intestines absorb
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| Large intestine | larger in diameter than small intestine, but shorter; extends from ileum of small intestine to anus; absorbs water, some electrolytes, some components of bile, some vitamins; eliminates indigestible food residue as feces
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| Ileocecal valve | located at junction of ileum and cecum; regulates movement of food residue from small intestine into large intestine
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| Cecum, appendix, colon, rectum, anal canal | subdivisions of large intestine
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| Cecum | sac-like beginning of large intestine in the lower, right portion of abdominal cavity
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| Appendix (vermiform appendix) | small, worm-shaped tubular structure attached to cecum; contains lymphoid tissue to combat bacteria, but an excessive accumulation of bacteria can cause inflammation
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| Appendicitis | inflammation of appendix due to excessive accumulation of bacteria; prone to rupture, which could cause extremely large number of bacteria to be released into abdominal cavity, which can lead to peritonitis
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| Colon | includes ascending, transverse, descending, and sigmoid portions
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| Ascending colon | portion of colon; from cecum extends up right side of abdominal cavity and makes turn near liver called hepatic flexure
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| Hepatic flexure | turn of ascending colon near the liver
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| Transverse colon | portion of colon extending horizontally across abdominal cavity from hepatic flexure to a turn near the spleen called the splenic flexure
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| Splenic flexure | turn of transverse colon near spleen
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| Descending colon | portion of colon; extends down left side of abdominal cavity from splenic flexure and to sigmoid colon
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| Sigmoid colon | portion of colon shaped somewhat like sideways “S” that extends from descending colon to rectum in posterior pelvic cavity
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| Rectum | subdivision of large intestine; extends straight down through the posterior pelvic cavity to anal canal
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| Anal canal | subdivision of large intestine; extends the length of about 1.5” from end of rectum to anus; surrounded by external anal sphincter and internal anal sphincter
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| External anal sphincter | anal sphincter consisting of skeletal muscle, so can be voluntarily controlled
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| Internal anal sphincter | anal sphincter consisting of smooth muscle; cannot be voluntarily controlled
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| Teniae coli | three longitudinal strips along colon; contain smooth muscle, so have muscle tone and cause the colon to pouch-up into pucker-like units called haustra (sing. Haustrum)
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| Diverticula | abnormal protrusions/outward herniations of mucosa through colon wall caused by greater exertion of pressure due to lack of fiber in diet; can result in diverticulosis or diverticulitis if inflamed or infected
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| Defecation | involves mass peristaltic movements that move feces into rectum and anal canal, and relaxation of anal sphincters
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| Hemorrhoids | varicosities of veins in anal canal; result from straining to defecate or deliver a baby
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