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Gastric Secretion And Digestion In The Stomach Notes

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Lecture 7 & 8 Gastric secretion and digestion in the stomach

Basic functions of stomach digestion o Reservoir- Gastric motility o Digest proteins- Pepsins o Essential for vit B12 absorption- Intrinsic factor (cells of the corpus) Gastric secretion o 1.5-2.5 litres per day; pH 0.9-1.5 o Composition: HCl, pepsins (pepsinogen first), intrinsic factor, mucus & HCO3(keeps lining of stomach intact in presence of acid) Gastric mucosa divided into 3 regions o CARDIAC GLANDULAR REGION
 Main function is mucus secretion
 Not very many acid secreting cells o OXYNIC GLANDULAR REGION
 Few gastrin & histamine producing cells (regulatory molecules)
 Secrete: HCl, intrinsic factor, pepsinogens, mucus, histamine o PYLORIC GLANDULAR REGION
 Secrete: Mucus, Gastrin, Somatostatin (last two= regulatory molecules)
 Won't see gland producing acid Structure of gastric mucosa o Gastric pits (G cells)= Gastrin o Surface epithelial cells= Mucus, HCO3o Mucus neck cells= Mucus o Parietal cell= HCl, Intrinsic factor o Chief cell= Pepsinogens o Endocrine cells= Histamine (ECL cell), Somatostatin (D cell) Secretion of HCl o Function of HCl
 Promote pepsin activation (from pepsinogen)
 Kill/inhibit microorganisms
 Stimulate secretions in small intestine
 Helps iron & calcium absorption in small intestine (WON'T BE TESTED) o Morphological changes that accompany HCl secretion
 Resting parietal cells

• Tubulovesicles (released into apical membrane, signal)

• Not a large surface area (no finger like projections)
 Active parietal cells

• Larger secretory membrane, more H+ pumps, K+ and Clchannels

• Increase in surface area (finger like projections)

• Total transport across membrane= Number transporters X Active o Cellular mechanisms of HCl secretion

1. H+/K+ ATPase uses energy to pump out H+ ions into lumen and K+ in

2. Apical membrane K+ channels recycle K+ ions across apical membrane

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