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18 Cards in this Set
- Front
- Back
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HCl |
-Secreted by parietal cells -Secreted in fundus/body -Kills bacteria and allows activation of pepsin from pepsinogen -Provides low pH for pepsin action |
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Pepsinogen |
-Secreted by peptic/chief cells -Secreted in fundus/body -Is the inactive proenzyme of pepsin |
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Intrinsic Factor |
-Secreted by parietal/oxyntic cells -Secreted in fundus/body -Is a glycoprotein required for normal absorption of vitamin B12 -ESSENTIAL |
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Mucus and HCO3- |
-Secreted by Mucous neck cells and epithelial cells -Secreted everywhere -Important for formation of gastric mucosa (protection) against acidic and peptic luminal environment |
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Histamine |
-Secreted by Enterochromaffin-Like Cells (ECL) -Secreted in fundus/antrum -Most powerful stimulator of HCl secretion -Acts paracrine |
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Somatostatin |
-Secreted by D cells -Secreted in stomach, pancreas, small intestine -Powerful inhibitor of HCl secretion -Acts endocrine |
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Gastrin |
-Secreted by G cells -Secreted in pyloric region -HCl secretagogue -Acts endocrine |
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Mechanism of Gastric Acid Secretion |
-Parietal cells activated: tubulovesicular system fuses with plasma membrane of secretory canaliculi, increasing number of H/K antiporters -Intracellularly: carbonic anhydrase makes H2CO3 from CO2 and H2O, H2CO3 dissociates into H+ and HCO3- -Lumen (apical membrane): H+ pumped out into lumen via H/K ATPase -Cl- follows H+ via diffusion -Basolateral membrane: HCO3- absorbed back into blood via Cl/HCO3 exchanger |
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Mechanism of Bicarbonate Secretion |
-Surface epithelium secretes a watery fluid containing Na, Cl, K, HCO3 -[K] and [HCO3] are higher that plasma, and HCO3 is trapped by viscous mucus |
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Acetylcholine stimulation of H+ secretion |
-Released from vagus nerve innervating gastric mucosa -Binds to muscarinic receptors on parietal cells -2nd messengers: IP3/Ca2+, stimulates H+ secretion |
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Atropine |
-Blocks Acetylcholine effects on parietal cells -Inhibits muscarinic recptors -Blocks ach-potentiated effects of histamine and gastrin |
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Histamine stimulation of H+ secretion |
-Released by ECL cells, act paracrine on parietal cells -Binds to H2 receptors -2nd messenger: cAMP, stimulates H+ secretion by parietal cells |
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Cimetidine |
-Blocks histamine effect -Blocks H2 receptors -Blocks histamine potentiated effect of Ach and gastrin |
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Gastrin stimulation of H+ secretion |
-Secreted into circulation by stomach G cells -Endocrine effect on parietal cells -2nd messengers: IP3/Ca2+ |
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Omeprazole |
-Blocks H+/K+ ATPase on lumenal membrane -Prevents H+ secretion |
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Histamine potentiation |
-Histamine potentiates actions of Ach and gastrin |
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Acetylcholine potentiation |
-Ach potentiates actions of histamine and gastrin |
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Feedback Inhibition of Gastric Acid Secretion |
-Acidic chyme (pH > 3) in antrum causes release of somatostatin (SS) by D cells -Direct: SS binds to receptors in parietal cells, inhibits stimulatory effect of histamine -Indirect: SS inhibits histamine release from ECL cells, gastrin release from G cells |
