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Digestion Structure of the wall of the GI tract Sphincters Gastric emptying Vomiting Exocrine glands Have ducts Epithelium is continuous w/ body surface Ex: Salivary, gastric glands, pancreas, bile glands in liver, sweat glands http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/E/ExocrineGlands.html Wall of the GI Tract Mucous Membrane Epithelium (varies) Lamina propria (Connective tissue) Muscularis Mucosa (smooth muscle) Submucosa Muscularis Externa, Serosa Muscularis Externa: 2 layers of smooth muscle Inner circular fibers Outer longitudinal fibers Neural network in between Enteric nervous system Serosa: outermost layer Connective tissue Squamous cells Muscularis Externa Layers Sphincters UES LES Pyloric Ileocecal Internal anal External anal GI secretions Gastric: Gastrin: gastric juice secretion Enterogastrones: Secretin: bicarbonate from pancreas • CCK: • bile (contractions from gall bladder) in response to amino, fatty acids • pancreatic enzymes Gastric Emptying Needs to be mediated so rate of emptying into the small intestine isn’t greater than rate of small intestine processing Presence of acid in the duodenom secretin closes pyloric sphincter, stimulates secretions of the pancreas Presence of fat: release of CCK closes pyloric sphincter Presence of peptides/amino acids: release of gastrin closes pyloric sphincter Yaking, spewing, blowing chunks, hurling, etc. (vomiting) Reflex, expulsion of stomach/duodenal contents Retching: contents forced into esophagus, not up to pharynx Reverse peristalsis Pyloric sphincter relaxes Yaking (continued) “vomiting center” in medulla signaled by: Distension of stomach, pressure in the back of the throat Injury to urogenital area Dizziness Emetics: stimulate stomach/duodenum receptors to induce vomiting Ex: ipecac