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WEEK 2:
Physiology of the digestive system 1:
| Question | Answer |
|---|---|
| how much food can be stored in the stomach | volume of 4L when fully distended |
| stomach functions | storage area for food that has been swallowed, mechanically digest food that has been swallowed, begin process of digestion of proteins in swallowed food, and to produce chyme and release controlled amounts of this to the duodenum |
| exocrine gastric secretions (into lumen) | hydrochloric acid, intrinsic factor, pepsinogen, and mucus |
| endocrine gastric secretions (into the blood) | gastrin and somatostatin |
| paracrine gastric secretions (acts local to its release) | histamine |
| parietal cells in upper region of body make | HCL and intrinsic factor |
| chief cells and G cells in lower region of body make | pepsinogen and gastrin |
| where are parietal cells in stomach | upper region of body |
| where are chief cells and G cells in stomach | lower region of body |
| enterochromaffin like cells (ECLs) near parietal cells make | histamine |
| where are enterochromaffin like cells (ECLs) in stomach | near parietal cells |
| D cells in antrum make | somatostatin |
| where are D cells in stomach | in antrum |
| role of HCL | acidifies lumen and produces pepsin from pepsinogen |
| intrinsic factor function | important in absorption of vitamin B12 (later in terminal ileum( and erythropoiesis |
| pepsinogen function | precursor of pepsin (acts as an endopeptidase) |
| function of mucus | protects mucosal surface being damaged by HCL |
| gastrin function | stimulates acid production both directly and via histamine |
| histamine function | stimulates acid production |
| somatostatin function | inhibits release of gastrin |
| vagal nerve activity (via M3 receptors) stimulates what indirect and direct functions (2) | direct effect on parietal cells and indirect effect via gastrin (CCK-B receptors) and histamine (H2 receptors) |
| effect of prostaglandins | increase secretion of mucus |
| what do tissue prostaglandins and somatostatins do | inhibit acid secretion |
| phases of gastric secretion | cephalic phase, gastric phase and intestinal phase |
| cephalic phase | thought, smell, sight and taste of food releases ACh stimulating the parietal cells and also G cells (vagally mediated) with 40% gastric acid secretion occuring here |
| gastric phase | distension and reflex activation of enteric neurons and vagal outflow stimulate parietal cells and G cells and digested proteins in stomach also stimulate G cells (about 50% gastric acid secretion occurs here) |
| how much gastric acid secretion occurs in cephalic phase | 40% |
| how much gastric acid secretion occurs in gastric phase | 50% |
| how much gastric acid secretion occurs in intestinal phase | 10% |
| intestinal phase | amino acids present in bloodstream and directly stimulate parietal cells with 10% gastric acid secretions occurring here |
| inhibition of gastric secretion includes | gastric mechanism and duodenal mechanism |
| gastric mechanism | if proteins are present in stomach they act as buffers to keep luminal pH >3 and as stomach empties the luminal pH falls below 3 and D cells release somatostatin to inhibit gastrin release and reduce acid secretion |
| duodenal mechanism | acidification of duodenal lumen releases secretin from S sells which inhibits gastrin secretion and this also the present of fatty acids and salt in duodenum release gastric inhibitory peptide which acts directly on parietal cells to inhibit HCL secretion |
| where is peristalsis in stomach | lower part |
| how does churning occur and slow gastric emptying | via action of peristalsis and pyloric valve |
| rate of gastric emptying is controlled to some extent by | caloric value of contents of the duodenum |
| which part of GIT in which motility is most likely to be influenced by hormones | upper GIT |
| hormonal influences role in stomach | ensure stomach empties at correct rate and that appropriate pancreatic and biliary secretions are released |
| examples of hormones used in stomach | CCK, gastrin, motilin, and secretin |
| gastrin stimulated by | stomach distension |
| secretin stimulated by | fat and partially digested protein in duodenal lumen |
| cholecystokinin stimulated by (CCK) | acidification of duodenal contents |
| gastric inhibitory peptide (GIP) stimulated by | nutrients (especially glucose) in small intestine |
| motilin stimulated by | alkaline state of duodenal contents |
| gastrin is made by | stomach G cells |
| CCK is made by | I cells in small intestine |
| secretin is made by | small intestine S cells |
| GIP is made by | small intestine K cells |
| motilin is made by | duodenum - M (or Mo) cells |
| gastrin action | relax cardia, increase antral activity, increase gastric acid secretion |
| CCK function | relaxes stomach, contracts gallbladder, and increases pancreatic secretion |
| secretin function | relaxes stomach and increases HCO3- secretion by pancreas |
| gastric inhibitory peptide (GIP) function | decrease gastric acid secretion and increase insulin secretion |
| motilin function | increase gastric acid secretion increase stomach activity |
Created by:
22tango
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