Digestive System Part 3

Small Intestine Duodenum: smallest section Jejunum: middle section Stomach empties here Jejunum: middle section Ileum: final section Joins large intestine at ileocecal sphincter

Small Intestine 21 feet of small intestine with added structures to increase surface area Almost all absorption occurs here Circular folds: folds in the mucosa to splash chyme and enhance absorption Villi: fingerlike projections that contain capillaries, arteries, veins, all to move absorbed substances quickly

Small Intestine Microvilli: smaller projections on the villi to further increase surface area and absorption

Small Intestine Intestinal glands: in mucosa that secrete intestinal juice Clear, yellowish liquid quickly reabsorbed pH 7.6 with water and mucous Enzymes for Chemical Digestion: Maltase, sucrose, lactase: disac. To monosa. Peptidases: peptides to amino acids Ribonuclease, dioxyribonuclease: nucleic acids

Small Intestine Mechanical Digestion: Segmentation: Concentration of chyme and juice that sloshes between areas of contraction of the muscularis Perstalsis: moves the chyme steadily through intestines

Absorption in Small Intestine Passage of digested substances and nutrients from the lumen to into the blood or lymph 90% of all absorption takes place here Substances absorbed by diffusion, osmosis, and active transport

Absorption in Small Intestine Carbohydrates absorbed as monosaccharides Proteins absorbed as amino acids Lipids absorbed as monoglycerides and fatty acids Water —9 liters enter daily and 8 are reabsorbed

Large Intestine Main functions: Completion of absorption Manufacture certain vitamins Formation of feces Elimination of feces

Large Intestine Cecum: pouch after ileocecal sphincter Colon: ascending, transverse, descending, sigmoid Surface area increased by pouch-like divisions: haustra Rectum: last part, stores waste Last inch is anal canal Anus: opening to exterior Two sphincters: internal anal sphincter (involuntary), external anal sphincter (voluntary)

Chemical Digestion of Lrg. Intestine No enzymes Bacteria ferment remaining carbohydrates Release hydrogen, carbon dioxide, and methane Vitamins K and some B’s are made and absorbed

Mechanical Digestion of Lrg. Intestine Haustral churning: walls contract when haustra fill to a certain level Peristalsis: slower than other areas Mass peristalsis: strong muscular wave that pushes waste into the rectum

Absorption & Feces Formation Chyme in the colon for 3-10 hrs. becomes rather solid: feces Water, epithelial cells from mucosa, bacteria, undigested food All but 100mL of the 1L of water is absorbed

Defecation Emptying of the rectum Diarrhea: not enough water is absorbed because chyme travels too quickly through intestine Can cause dehydration Constipation: feces remains in colon too long, almost all the water is absorbed

Digestive System Attachments Peritoneum & serosa: secrete slippery fluid to glide organs over each other Outermost layer of GI tract Visceral peritoneum: covers some organs in abdominal cavity Parietal peritoneum: the walls of the abdominal cavity

Digestive System Attachments Mesentery: binds small intestine to posterior abdominal wall Mesacolon: binds large intestine to posterior abdominal wall Falciform ligament: attaches liver to the anterior abdominal wall and diaphragm

Digestive Disorders Ulcers: lesions in a membrane Peptic —from gastric juice Gastric —in stomach Esophageal —in esophagus Duodenal —in small intestine Appendicitis: inflammation of appendix

Digestive Disorders Cirrhosis: scarred liver due to chronic inflammation Colitis: inflammation of colon and rectum Hernia: protrusion of an organ through a membrane or cavity wall