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## BRS Physiology ### C. Inhibition of Gastrin Secretion - **H+ in the lumen of the stomach inhibits gastrin release. This negative feedback control ensures that gastrin secretion is inhibited if the stomach contents are sufficiently acidic.** - **Somatostatin inhibits gastrin release.** - **Zolli...

## BRS Physiology ### C. Inhibition of Gastrin Secretion - **H+ in the lumen of the stomach inhibits gastrin release. This negative feedback control ensures that gastrin secretion is inhibited if the stomach contents are sufficiently acidic.** - **Somatostatin inhibits gastrin release.** - **Zollinger-Ellison Syndrome (gastrinoma) occurs when gastrin is secreted by non-β-cell tumors of the pancreas.** ### 2. CCK - **Contains 33 amino acids.** - **Is homologous to gastrin. The five C-terminal amino acids are the same in CCK and gastrin. The biologic activity of CCK resides in the C-terminal heptapeptide. Thus, the heptapeptide contains the sequence that is homologous to gastrin and has both CCK and gastrin activity.** ### a. Actions of CCK - **Stimulates contraction of the gallbladder and simultaneously causes relaxation of the sphincter of Oddi for secretion of bile.** - **Stimulates pancreatic enzyme secretion.** - **Potentiates secretin-induced stimulation of pancreatic HCO3- secretion.** - **Stimulates growth of the exocrine pancreas.** - **Inhibits gastric emptying. Thus, meals containing fat stimulate the secretion of CCK, which slows gastric emptying to allow more time for intestinal digestion and absorption.** ### b. Stimuli for the Release of CCK - **CCK is released from the I cells of the duodenal and jejunal mucosa by** - **Small peptides and amino acids.** - **Fatty acids and monoglycerides. Triglycerides do not stimulate the release of CCK because they cannot cross intestinal cell membranes.** ### 3. Secretin - **Contains 27 amino acids. Is homologous to glucagon; 14 of the 27 amino acids in secretin are the same as those in glucagon. All of the amino acids are required for biologic activity.** ### a. Actions of Secretin - **Are coordinated to reduce the amount of H+ in the lumen of the small intestine.** - **Stimulates pancreatic HCO3- secretion and increases growth of the exocrine pancreas. Pancreatic HCO3- neutralizes H+ in the intestinal lumen.** - **Stimulates HCO3- and H2O secretion by the liver and increases bile production.** - **Inhibits H+ secretion by gastric parietal cells.** ### b. Stimuli for the Release of Secretin - **Secretin is released by the S cells of the duodenum in response to** - **H+ in the lumen of the duodenum.** - **Fatty acids in the lumen of the duodenum.** ### 4. GIP - **Contains 42 amino acids. Is homologous to secretin and glucagon.** #### a. Actions of GIP