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## Gastrointestinal hormones, paracrines, and neurocrines **a. Actions of gastrin:** * Increases H+ secretion by the gastric parietal cells. * Stimulates growth of gastric mucosa by stimulating the synthesis of RNA and new protein. Patients with gastrin-secreting tumors have hypertrophy and hyperp...

## Gastrointestinal hormones, paracrines, and neurocrines **a. Actions of gastrin:** * Increases H+ secretion by the gastric parietal cells. * Stimulates growth of gastric mucosa by stimulating the synthesis of RNA and new protein. Patients with gastrin-secreting tumors have hypertrophy and hyperplasia of the gastric mucosa. **b. Stimuli for secretion of gastrin:** * Gastrin is secreted from the G cells of the gastric antrum in response to a meal. * Gastrin is secreted in response to the following: * Small peptides and amino acids in the lumen of the stomach. * The most potent stimuli for gastrin secretion are phenylalanine and tryptophan. ## Summary of Gastrointestinal (GI) Hormones | Hormones | Homology (Family) | Site of Secretion | Stimulus for Secretion | Actions | |-------------------|---------------------|------------------------|--------------------------------------------------------------|----------------------------------------------------------------------------------| | Gastrin | Gastrin-CCK | G cells of stomach | Small peptides and amino acids Distention of stomach Vagus (via GRP) Inhibited by H+ in stomach Inhibited by somatostatin | ↑ Gastric H+ secretion Stimulates growth of gastric mucosa | | CCK | Gastrin-CCK | I cells of duodenum and jejunum | Small peptides and amino acids Fatty acids | Stimulates contraction of gallbladder and relaxation of sphincter of Oddi ↑ Pancreatic enzyme and HCO3- secretion ↑ Growth of exocrine pancreas/gallbladder Inhibits gastric emptying | | Secretin | Secretin-glucagon | S cells of duodenum | H+ in duodenum Fatty acids in duodenum | ↑ Pancreatic HCO3- secretion ↑ Biliary HCO3- secretion ↑ Gastric H+ secretion | | GIP | Secretin-glucagon | Duodenum and jejunum | Fatty acids, amino acids, and oral glucose | ↑ Insulin secretion ↑ Gastric H+ secretion | * CCK, cholecystokinin; GIP, glucose-dependent insulinotropic peptide. GRP, gastrin-releasing peptide.