GI Hormones Flashcards
Gastrin
Source: G cells (antrum of stomach)
Action: Increased gastric H+ secretion
Increased growth of gastric mucosa
Increased gastric motility
Regulation: Increased by stomach distention/alkalinization, amino acids, peptides, vagal stimulation
Decreased by stomach pH < 1.5
Notes: Increased in Zollinger-Ellison syndrome.
Increased by chronic PPI use.
Phenylalanine and tryptophan are potent stimulators.
Cholecystokinin
Source: I cells ( duodenum, jejunum)
Action: Increased pancreatic secretion
Increased gallbladder contraction
Decreased gastric emptying
Increased sphincter of Oddi relaxation
Regulation: Increased by fatty acids, amino acids
Notes: CCK acts on neural muscarinic pathways to cause pancreatic secretion.
Secretin
Source: S cells (duodenum)
Action: Increased pancreatic HCO3- secretion
Decreased gastric acid secretion
Increased bile secretion
Regulation: Increased by acid, fatty acids in lumen of duodenum
Notes: Increased HCO3- neutralizes gastric acid in duodenum, allowing pancreatic enzymes to function.
Somatostatin
Source: D cells (pancreatic islets, GI mucosa)
Action: Decreased gastric acid and pepsinogen secretion
Decreased pancreatic and small intestine fluid secretion
Decreased gallbladder contraction
Decreased insulin and glucagon release
Regulation: Increased by acid
Decreased by vagal stimulation
Notes: Inhibitory hormone. Antigrowth hormone effects (inhibits digestion and absorption of substances needed for growth).
Glucose-dependent insulinotropic peptide
Source: K cells (duodenum, jejunum)
Action:
Exocrine: Decreased gastric H+ secretion
Endocrine: Increased insulin release
Regulation: Increased by fatty acids, amino acids, oral glucose
Notes: Also known as gastric inhibitory peptide (GIP). An oral glucose load is used more rapidly than the equivalent given by IV due to GIP secretion.
Vasoactive intestinal polypeptide (VIP)
Source: Parasympathetic ganglia in sphincters, gallbladder, small intesting
Action: Increased intestinal water and electrolyte secretion
Increased relaxation of intestinal smooth muscle and sphincters
Regulation: Increased by distention and vagal stimulation
Decreased by adrenergic input
Notes: VIPoma-non-alpha, non-beta islet cell pancreatic tumor that secretes VIP. Copious Watery Diarrhea, Hypokalemia and Achlorhydria (WDHA syndrome).
Nitric oxide
Source:
Action: Increased smooth muscle relaxation, including lower esophageal sphincter
Regulation:
Notes: Loss of NO secretion is implicated in increased lower esophageal tone of achalasia.
Motilin
Source: Small intestine
Action: Produces migrating motor complexes (MMCs)
Regulation: Increased in fasting state
Notes: Motilin receptor agonists (such as erythromycin) are used to stimulate intestinal peristalsis.
