Gastrin – produced by G cells in stomach antrum

•  Secretion stimulated by amino acids, vagal input (acetylcholine), calcium, ETOH, antral distention, pH > 3.0

•  Secretion inhibited by pH < 3.0, somatostatin, secretin, CCK

•  Target cells – parietal cells and chief cells

•  Response – ↑ HCl, intrinsic factor, and pepsinogen secretion

•  Omeprazole blocks H/K ATPase of parietal cell (final pathway for H⁺ release)

  Somatostatin – mainly produced by D (somatostatin) cells in stomach antrum

•  Secretion stimulated by acid in duodenum

•  Target cells – many; is the great inhibitor

•  Response – inhibits gastrin and HCl release; inhibits release of insulin, glucagon, secretin, and motilin; ↓ pancreatic and biliary output

•  Octreotide (somatostatin analogue) – can be used to ↓ pancreatic fistula output

  CCK – produced by I cells of duodenum

•  Secretion stimulated by amino acids and fatty acid chains

•  Response – gallbladder contraction, relaxation of sphincter of Oddi, ↑ pancreatic enzyme secretion

  Secretin – produced by S cells of duodenum

•  Secretion stimulated by fat, bile, pH < 4.0

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