Gastrointestinal (GI) Hormones

Kaleb Martin Archer, MD
The Operative Review of Surgery. 2023; 1:52-58.

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Table of Contents

Hormones of the Stomach
Hormones of the Small Intestine
Hormones of the Pancreas

Mnemonics
References

Hormones of the Stomach

Gastrin Mn
  • Functions:
    • Stimulates Stomach Parietal Cells to Secrete HCl
      • Primarily Done by Stimulating Enterochromaffin-Like (ECL) Cells to Release Histamine 2
      • Also Has Some Direct Stimulation
    • Stimulates Stomach Chief Cells to Secrete Pepsinogen
    • Trophic Effects on Enterochromaffin-Like (ECL) Cells and Parietal Cells – Can Cause Mucosal Hyperplasia 3
  • Produced by G Cells of the Stomach 4
  • Stimulated By:
    • Amino Acids in the Stomach from Protein Digestion – Most Potent Stimulator
      • Phenylalanine and Tryptophan are the Strongest 5
    • Alkaline Environment
    • Acetylcholine from Vagal Stimulation
    • Gastric Distention
    • Bombesin (Gastrin-Releasing Peptide)
  • Inhibited By:
    • HCl in the Stomach – Negative Feedback
    • Somatostatin
  • Multiple Forms: G34 (Big Gastrin), G17 (Little Gastrin), etc
Somatostatin (SS) Mn
  • Functions:
    • Inhibits Stomach Parietal Cells to Decrease HCl Secretion 6
    • Inhibits Gastric Emptying
    • Inhibits Pancreatic Secretion (Insulin, Glucagon, and Pancreatic Enzymes)
    • Inhibits Bile Secretion 7
    • Inhibits Growth Hormone, Thyroid Stimulating Hormone, and Procalcitonin in the Hypothalamus
    • Inhibits Intestinal Transport of Nutrients
    • Inhibits Splanchnic Blood Flow 8
  • Produced by Delta (D) Cells of the Stomach, Duodenum, and Pancreas 9
  • Stimulated By:
    • Acid in the Duodenum 9
  • Inhibited By:
    • Acetylcholine from Vagal Stimulation 9
  • Two Forms: SS-14 and SS-28
  • Octreotide is a Somatostatin Analog Used for Various Treatments 10
Ghrelin Mn
  • Function:
    • Stimulates Hunger – Primary Function
    • Increases Gastric Emptying and Acid Secretion 9
    • May Raise Blood Glucose 11
  • Produced by Enterochromaffin Cells of the Stomach & Duodenum
  • Levels are Highest Before Meals
  • Levels are Significantly Decreased After Gastric Bypass – Enhances Weight Loss 12

Stomach 1

Hormones of the Small Intestine

Cholecystokinin (CCK) Mn
  • Functions:
    • Stimulates Gallbladder Contraction 13
    • Stimulates Sphincter of Oddi Relaxation 14
    • Stimulates Acinar Cells of the Pancreas to Secrete Digestive Enzymes 15
    • Suppresses Hunger 16
  • Produced by I Cells of the Duodenum 17
  • Stimulated By:
    • Amino Acids and Fatty Acids in the Duodenum – Strongest Stimulator 17
    • Acetylcholine from Vagal Stimulation 17
    • CCK-Releasing Peptide (Monitor Peptide) 18
  • Inhibited By:
    • Somatostatin – By Inhibition of CCK-Releasing Peptide 19
Secretin Mn
  • Functions:
    • Stimulates Bicarbonate Secretion in the Pancreas – Primary Action 20
    • Stimulates Bile Secretion 20
    • Inhibits Gastrin Secretion 21
    • Inhibits Stomach Parietal Cells to Decrease HCl Secretion 21
    • Inhibits Gastric Motility 21
  • Produced by S Cells of the Duodenum 22
  • Stimulated By:
    • Acid in the Duodenum – Primary Stimulator 20
    • Fatty Acids in the Duodenum 23
    • Bile Salts in the Duodenum 23
Motilin Mn
  • Primary Function: Stimulates Peristalsis and Gut Motility 21
    • By Stimulating the Migrating Myoelectric Complex (MMC)
    • Initiated in the Stomach Antrum and Propagates Distally 21
    • Secretion Peaks Every 100 Minutes Between Meals to Control Inter-Digestive Phase III Contractions 24
    • “Housekeeper of the Gut” by Clearing Out and Making Ready for the Next Meal
  • Produced by Mo Cells of the Duodenum and Jejunum 25
  • Stimulated By: 26
    • Bile
    • Free Fatty Acids
    • Duodenal Acid
    • *Overall Stimulation is Poorly Understood
  • Erythromycin (Antibiotic) Stimulates Motilin and is Often Used to Stimulate GI Motility 27
Incretins (GIP and GLP-1)
  • Definition: Hormones That Augment Insulin to Decrease Blood Glucose Levels
  • Gastric Inhibitory Peptide (GIP)
    • Also Known As: Glucose-Dependent Insulinotropic Polypeptide
    • Functions:
      • Stimulates Insulin Secretion – Primary Function 28
      • Weak Gastric Acid Inhibitor – Traditional Effect the Peptide Was Named For 29
    • Produced by K Cells of Duodenum 30
    • Stimulated by Glucose in the Duodenum
  • Glucagon-Like Peptide-1 (GLP-1)
    • Primary Function: Stimulates Insulin Secretion 31
    • Produced by L Cells of the Ileum and Colon 32
      • Some in the Duodenum and Jejunum as Well
    • Stimulation Not Inhibited by Type 2 Diabetes 33
Additional Hormones
  • Glucagon-Like Peptide-2 (GLP-2)
    • Functions: 34
      • Enhancement and Growth of Intestine
      • Stimulates Gastric Acid Secretion
    • Produced by L Cells of the Ileum and Colon (Co-Secreted with GLP-1) 34
    • Analogs Used to Treat Short Bowel Syndrome 35
  • Vasoactive Intestinal Polypeptide (VIP)
    • Functions: 36
      • Stimulates Intestinal Secretion and Absorption
      • Stimulates Bile Secretion
      • Stimulates Vasodilation
      • Relaxes Smooth Muscle (Lower Esophageal Sphincter and Colon)
    • Primarily Secreted by Neurons 37
  • Peptide YY (Peptide Tyrosine Tyrosine)
    • Functions:
      • Inhibits Gastric Emptying and Intestinal Motility 38
      • Inhibits Pancreatic Secretion 39
      • Inhibits Gallbladder Contraction 40
      • Stimulates Water and Electrolyte Absorption in the Colon
      • Inhibits Appetite 41
    • Produced by L Cells of the Ileum and Colon 42
    • Stimulated by Protein and Fat 43
  • Bombesin
    • Functions:
      • Stimulates Gastrin Release and Gastroprotection 44
      • Stimulates Cholecystokinin (CCK) Release 45
      • Negative Feedback to Stop Eating Behavior – Second Only to CCK 46,47
    • Produced Throughout the GI Tract and Brain

Duodenum 1

Hormones of the Pancreas

Hormones of the Pancreas

Mnemonics

Hormone Secreting Cells

  • G-G: G Cells Secrete Gastrin
  • D (Double-SS): D Cells Secrete Somatostatin
  • S (Single-S): S Cells Secrete Secretin
  • I-CCK (“Icky”): I Cells Secrete CCK

Gastric Hormone Functions

  • Gastrin: “Gastrin-Gastric”
    • Gastrin Stimulates Gastric Specific Functions
  • Somatostatin: S-STATIN – STASIS
    • “Stasis” Inhibits All Other Functions
    • Known as “The Great Inhibitor”
  • Ghrelin: “Ghrelin Growls”
    • Ghrelin Stimulates Hunger

Small Intestine Hormone Functions

  • Cholecystokinin: Chole, “Bile”; Cysto, “Sac”; Kinin, “Move”
    • Greek Origin Equates to Gallbladder Contraction
  • Secretin: Secretin-Secretes
    • Stimulates Bile and Pancreatic Bicarbonate Secretion
  • Motilin: Motilin-Motility
    • Stimulates Motility

References

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