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ANPS 020 February 24, 2012 Stomach (4) areas- 3 jobs 1. Cardiac -mucous cells secrete -junction with esophagus and sphincter (sm. Muscle) 2. Fundus and body (basically the same) -mucous cells secrete -chief cells (pepsinogen) specialized cells -parietal cells (H+; Cl- and IF) 3. Pyloric -mucous cells secrete -junction with duodenum and sphincter (sm. Muscle) FUNDUS/BODY Mucous cells – mucous Stem cells – differentiate to form all other cells) Parietal cells (HCL and IF –B12) Chief Cells (digestive enzyme – pepsinogen) MUCOUS CELS Store product in vesicles in the apical part of the cell Release of product by exocytosis Product goes to the lumen of the GI system Mucous cells make mucous and HCO3 (bicarbonate to neutralize acid) PROTECTING THE STOMACH CELLS Tight junctions – inhibit any movement through lateral portion of cells Mucous layer HCO3 from mucous cells helps neutralize stomach acid PARIETAL CELL Produces H+ and ClProduces intrinsic factor – B12 absorption Why have a pH of 2 in stomach??? 1. Acid helps kill bacteria 2. A pH of 2 is optimal pH for pepsin activity (enzyme) and helps start digestion Acid production Diffusion of Cl- ion thru membranes Exocytosis of intrinsic factor (IF) for B12 absorption Chief Cells Store product in vesicles in the apical part of the cell Release product by exocytosis Product foes to the lumen of the GI system Chief Cell synthesize and release pepsinogen = zymogen ENTEROENDOCRINE CELLS: Like taste buds in the GI epithelium Stimulants: proteins, carbohydrates, lipids, etc. Results: release peptide hormones…hormones result in many effects Function via paracrine and endocrine mechanisms Ex. = G cells in stomach epithelium release gastrin – stimulates acid secretion in stomach... by parietal cells CEPHALIC PHASE Sight, smell, thought of food causes: -CNS (extrinsic) stimulation of sub mucosal plexus (parasympathetic cells) Causes secretion of 1. Mucous cells --- mucous 2. Parietal cells --- HCL (acid) and Intrinsic factor (IF) 3. Chief cells ------ pepsinogen Prepares stomach to receive food Also causes muscle to contract GASTRIC PHASE (FOOD IN STOMACH) Once food enters the stomach, the influence of the CNS remains – sensory feedback foes to the CNS and information (efferent) returns to the nervous system of the gut Neural control of the digestive system from sensory input is managed by the intrinsic – enteric nervous system STIMULI: 1. Food takes up space –mechanoreceptors (stretch) receptors recognize bulk 2. The acid secreted into the lumen – chemoreceptors recognized acid 3. Digestion products from proteins – enteroendocrine (G cells) recognize peptides GASTRIC PHASE – EXTRINSIC CONTROL Regulation of acid secretion 1. Vagal input via enteric neurons provides input to parietal cell, ECL cells (histamine) and G cell (gastrin) 2. G cells releases gastrin activates parietal cells and ECL cells 3. ECL cell releases histamine – activates parietal cells 4. D cell releases somatostatin which inhibits parietal cells Mechanoreceptors and chemoreceptors stimulate: 1. Intrinsic enteric plexuses 2. Extrinsic sensory fibers Enteroendocrine cells sense peptides causes:: Cells secrete and muscles contract Mucous cells, Parietal cells, Chief Cells ----- mucous, HCL, pepsinogen G cells – gastrin->circulation ->stimulates chief and parietal cells and muscle contraction GASTRIC PHASE- INTRINSIC INPUT Receptors: mechano- & chemo-receptors stimulate GI plexuses GI plexuses stimulates cells to secrete and muscles to contract Peptides stimulate G cells that release gastrin Gastrin stimulates cells to secrete and muscles to contract Stimuli = lumen contents Neurons in the GI and hormones control the results WHAT HAPPENS TO CHYME (FOOD AND ACID) IN THE SMALL INTESTINE DIGESTION AND ABSORPTION ARE IMPORTANT HERE Acid has to be neutralized Pancreas release digestive enzymes and bicarbonate – rich fluid Liber makes bile for lipid absorption Gallbladder releases bile Digestion continues Water added and reabsorbed Absorption of building blocks through enterocytes Undigested material remains DUODENUM The folds in the lumen = plicae circulares -similar to rugae in the stomach but permanent Core of submucosa 4 LAYERS OF DIGESTIVE SYSTEM 1. Mucosa: - epithelium – plicae/villi - lamina propria (CT) - muscularis mucosa 2. Submucosa (CT) - submucosal glands 3. Muscularis externa - inner circular - outer longitudinal 4. Adventitia (mostly) DUODENUM – STRUCTURE AND FUNCTION Duodenum receives acidic chime from the stomach -list all its functions 1. Protect the epithelial cells from destruction - neutralize the acid from stomach - protect from digestive enzymes – from pancreas 2. Continue digesting of food and being to absorb the nutrients 3. Signal the stomach that is has the food and the stomach can adjust or stop its work DUODENUM – STRUCTURE AND FUNCTION Mucous covers or hides the epithelial cells -mucous from the submucosal (Brunner’s) glands Raise the PH from ~2 to about ~7 -bicarbonate rich alkaline fluid from: -pancreas -submucosal (Brunner’s) gland Together – mucous covers epithelial cells and alkaline watery secretions raise the pH to about 7 --if these don’t work, the stomach acid can cause an ulcer DUODENUM – STRUCTURE AND FUNCTION Digest the food and being to absorb the nutrients. Food contain carbohydrates, fats and proteins Receive digestive enzymes from pancreas Receive bile form liver/gallbladder to help absorb fats Increased cell surface area is designed to absorb nutrients (Can only absorb “Building blocks”) DUODENUM FUNCTIONS AND BEYOND Accessory organs of the digestive system 1. Discuss pancreas 2. Discuss liver and gallbladder functions 3. Return to absorptive functions of the small intestine PANCREAS FUNCTIONS 1. Secrete watery, bicarbonate – rich alkaline fluid (from duct cells) to neutralize stomach acid 2. Secrete digestive enzymes – an exocrine function to digest foods 3. Secrete hormones like insulin and glucagon etc. PNACREAS STRUCTURE AND FUNCTION Exocrine organ (polarized cells) -pancreatic acinar cells synthesize digestive enzymes -proenzymes (zygomens) -inactive in duodenum -secreted through ducts Pancreatic ducts cells secrete water and HCO3 (bicarbonate) Endocrine organ --islet of Langerhans -insulin -glucagon -others EXOCRINE PANCREAS Acinus cells: secrete pancreatic pro-enzymes -trysinogen, chymotrypsinogen (proteins) -lipases (fats) -Amylase and carbohydrase (carbohydrates) -trypsin activates pro-enzymes to allow digestion Duct cells secrete water and ions (dilate and buffer stomach acid)