Updated: 8/12/2021

Overview of GI Hormones

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Overview
 
Hormone
Source
Action Regulation Notes
Gastrin
  • G cells (stomach-antrum)
  • ↑ gastric H+ secretion
  • ↑ growth of gastric mucosa 
  • ↑ gastric motility
  • ↑ by stomach distension
  • ↑ by amino acids, small peptides
  • ↑ by vagal stimulation (GRP)
  • ↓ by stomach pH < 1.5
  • ↓ by somatostatin
  • ↑↑ in Zollinger-Ellison syndrome
  • Phenylalanine and tryptophan are potent stimulators
Cholecystokinin (CCK) 
  • I cells (duodenum, jejunum)
  • ↑ pancreatic secretion
  • ↑ gallbladder contraction and relaxation of sphincter of Oddi
  • ↓ gastric emptying
  • ↑ by amino acids, small peptides
  • ↑ by fatty acids
  • A patient with cholelithiasis (gallstones) experiences worsened pain after fatty food ingestion due to ↑ release of CCK 
Secretin  
  • S cells (duodenum)
  • ↑ pancreatic HCO3- secretion
  • ↑ biliary HCO3- secretion
  • ↓ gastric H+ secretion
  • ↑ by H+ in duodenum
  • ↑ by fatty acids in duodenum
  • ↑ HCO3- neutralizes gastric H+ in duodenum, essential for fat digestion (pancreatic lipases have pH optimums between 6 and 8)
Somatostatin
  • D cells ( GI mucosa)
  • delta cells (endocrine pancreas)
  • ↓ gastric H+ and pepsinogen secretion
  • ↓ pancreatic and small intestine fluid secretion
  • ↓ gallbladder contraction
  • ↓ insulin and glucagon release
  • ↑ by H+
  • ↓ by vagal stimulation
  • Inhibitory hormone
  • Antigrowth hormone effects (digestion and absorption of substances needed for growth)
  • Somatostatin is treatment for VIPoma and carcinoid tumors
Glucose-dependent insulinotropic peptide (GIP)
  • K cells (duodenum, jejunum)
  • exocrine: ↓ gastric H+ secretion
  • endocrine: ↑ insulin secretion by pancreatic beta cells
  • ↑ by fatty acids
  • ↑ by amino acids
  • ↑ by oral glucose
  • An oral glucose load is utilized by cells more rapidly than an equivalent IV glucose load
Vasoactive intestinal polypeptide (VIP)
  • parasympathetic ganglia in sphincters, gallbladder, and small intestine
  • ↑ intestinal water and electrolyte secretion
  • ↑ relaxation of intestinal smooth muscle and sphincters
  • ↑ by distention and vagal stimulation
  • ↓ by adrenergic input
  • VIPoma is a non-α, non-β islet cell pancreatic tumor that secretes VIP and causes copious diarrhea
Nitric oxide (NO)
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  • ↑ smooth muscle relaxation ( lower esophageal sphincter)
 -
  • Loss of NO secretion is implicated in ↑ lower esophageal tone of achalasia
Motilin
  • small intestine (upper duodenum)
  • increases GI motility
  • produces migrating motor complexes (MMCs)
  • ↑ in fasting state
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Ghrelin 
  • P/D1 cells (stomach)
  • ↑ growth hormone, ACTH, cortisol, and prolactin secretion
  • ↑ before meals
  • ↓ after meals
  • Regulates hunger, meal initiation
  • Lost following gastric bypass surgery
  • Associated with hyperphagia in Prader-Willi
Neuropeptide-Y 
  • neurons of sympathetic nervous system
  • ↑ appetite, ↓  energy expenditure
  • Ghrelin  release
  • Leptin ↓  release
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Glucagon-like peptide 1 (GLP-1)
  • L cells (endocrine cells of the intestinal epithelium)
  • ↑ glucose-induced insulin secretion from pancreatic β-cells
  • ↓ glucagon secretion
  • ↓ GI motility and secretions
  • Promotes satiety
  • Secreted in response to meal intake
  • Degraded by dipeptidyl peptidase IV
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