GI secretion and its regulation

6 important questions on GI secretion and its regulation

How is the secretion of saliva controlled?

By neural input to the salivary glands via both branches of the autonomic nervous system. Parasympathetic actively stimulates abundant secretion of watery saliva, sympathetic activity stimulates instant secretion of protein rich, viscous saliva.

How is saliva secretion regulated?

Regulated by the salivary center in the medulla oblongata.

How is the acid in the stomach secreted?

  • Acid secreted by the stomach is generated inside parietal cells by the reaction of CO2 with water, which is catalyzed by carbonic anhydrase (CA) and generates H+ and bicarbonate.
  • H+ is transported actively into the lumen of the stomach by pumps in the apical membrane that use ATP to transport H+ out and K+ in.
  • Bicarbonate is transported actively into the interstitial fluid through the basolateral membrane in exchange for Cl-.
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By what is the secretion of acid by the parietal cells stimulated?

Stimulated by parasympathetic nervous activity, gastrin and histamine when food is present in the stomach. Suppressed when food leaves the stomach.

What are the strongest influences on pancreatic juice secretion?

CCK and secretin, which are released in response to food in the duodenum.
  • CCK acts on acinar cells to stimulate enzyme secretion
  • Secretin acts on duct cells to stimulate secretion of bicarnonate-rich fluid.  

By what is the release of CCK and secretin mainly regulated?

  • Secretin: the acidity of the duodenal contents. More acidity --> more secretin secretion.
  • CCK: concentrations of protein digestion products and fat in the duodenum. Rises as chyme leaves the stomach.

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