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Stomach Stomach Structure • J-shaped, pouch-like organ that hangs inferior to diaphragm in upper left portion of abdominal cavity • capacity = 1L or more • empty = thick folds of mucousal and submucousal layers mark the stomach’s inner lining • full = no folds • pyloric sphincter controls gastric emptying into small intestine Gastric Glands 3 types of cells 1. mucous – thin, mucus secretion a. alkaline (basic) secretion keeps stomach from digesting itself 2. chief – digestive enzymes 3. parietal – HCl (hydrochloric acid) and intrinsic factor a. helps sm. intestine absorb vitamin B12 (helps keep nerves and RBC healthy) *pepsin – most important digestive enzyme; breaks proteins into polypeptides; secreted as pepsinogen (converted by HCl) Review Questions 1. What are the secretions of the chief cells and parietal cells? 2. What is the most important digestive enzyme? What does it do? 3. Why doesn’t the stomach digest itself? Regulation of Gastric Secretions • gastric juice (HCl and pepsinogen) secreted continuously – rate controlled neurally and hormonally • neural regulation – ACh stimulates release of gastric juice • hormonal regulation – gastrin increases release of gastric juice Just for Kicks • ulcers are open sores in skin and mucous membranes resulting from localized tissue damage • originally thought that stress triggered ulcers to occur, but 2 Australian scientists proved it was actually a bacterial infection (Heliobacter pylori) of the stomach lining by ingesting the bacteria Gastric Absorption • some water, certain salts, alcohol, and some lipid-soluble drugs Review Questions 1. What is gastric juice? 2. What controls gastric juice secretion? 3. What substances can the stomach absorb? Mixing and Emptying Actions • mixing movements of stomach wall produce a semi-fluid paste of food and gastric juice called chyme • peristaltic waves push chyme toward pyloric sphincter muscle relaxes stomach contractions push small amounts of chyme into sm. intestine • rate of emptying depends on fluidity of chyme and the type of food present • liquids < carbohydrates < proteins < fats • as chyme enters duodenum (1st part of sm intestine) accessory organs (pancreas, liver, gallbladder) add their secretions Just for Kicks • • vomiting is a complex reflex in which the stomach empties through the esophagus, pharynx, and mouth rather than through the sm intestine irritation or distention send impulses to the vomiting center of the medulla which then triggers the vomiting reflex Review Questions 1. How is chyme produced? 2. What factors influence how quickly chyme leaves the stomach?