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Pancreatic secretion

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Physiology 3120
Tom Stavraky

Human Physiology Friday, March 26, 2010 “Gastro IV” Down-regulation of gastric acid secretion • Very close to the secretory cells of the pyloric gland area is another cell that releases somatostatin (normally released by pancreas, but has a somewhat ubiquitous secretion)  Also under cholinergic control, but ACh inhibits somatostatin release  Somatostatin is inhibitory to acid secretion • As stimuli that activate cholinergic mechanisms, the cholinergic nerves are not activated, and have less ACh release  Less release of acid (from oxyntic) and gastrin (from G cell)  Somatostatin is disinhibited; and inhibits the release of gastrin  Eliminate the potentiated response of acid secretion  Acid itself has a stimulatory effect on somatostatin release; excess acid increases somatostatin, which decreases gastrin and therefore turns down acid secretion • But, you need acid for other things (i.e. intrinsic factor, pepsinogen  pepsin), so having it immediately turn itself off would be detrimental  The somatostatin cell is pH-sensitive  pH in stomach before eating is somewhere around 4-6 (foods such as proteins or carbs are relatively good buffers)  Eventually, so much acid is secreted that the buffering capacity is overwhelmed and the pH begins to drop; eventually, you reach the pH switch (between 2.4-2.7) that turns on the somatostatin cell, which inhibits gastrin  Antrum = archaic term for pyloric gland area Pancreatic Secretion • Pancreas composed of exocrine (95%) and endocrine tissues • Empties into the duodenum (the proximal part of small intestine)  Stomach is able to resist its own acid; but the mucosa of any other part of the GI tract is very sensitive to acid/fragile • 2 major functions of exocrine pancreas a) Production & secretion of digestive enzymes (i.e. proteins, carbohydrates, and fats) b) Secrete a bicarbonate-rich juice; why is bicarbonate important?  Buffer for intestines; need to protect mucosa from ulceration by acid  Restore pH to the optimal range for the digestive enzymes from point (a) above • Structurally very similar to the salivon (i.e. acinus with converging ducts)  Does not have a striated duct system; epithelial cells all along the duct look exactly the same  Different division of labour  In salivon, everything originated in acinus (juice & organic compounds); in pancreatic d
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