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Gastrointestinal ` gastrointestinal—anatomy Gastrointestinal ` gastrointestinal—PHysiology seCtion iii 371

` gastrointestinal—PHysiology

Gastrointestinal regulatory substances
regUlatory sUbstanCe soUrCe aCtion regUlation notes
Gastrin G cells (antrum  gastric H secretion  by stomach  by chronic PPI use
+
of stomach,  growth of gastric mucosa distention/  in chronic atrophic gastritis
duodenum)  gastric motility alkalinization, (eg, H pylori)
amino acids,  in Zollinger-Ellison
peptides, vagal syndrome (gastrinoma)
stimulation via
gastrin-releasing
peptide (GRP)
 by pH < 1.5
Somatostatin D cells  gastric acid and  by acid Inhibits secretion of various
(pancreatic islets, pepsinogen secretion  by vagal hormones (encourages
GI mucosa)  pancreatic and small stimulation somato-stasis)
intestine fluid secretion Octreotide is an analog used
 gallbladder contraction to treat acromegaly, carcinoid
 insulin and glucagon syndrome, and variceal
release bleeding
Cholecystokinin I cells (duodenum,  pancreatic secretion  by fatty acids, Acts on neural muscarinic
jejunum)  gallbladder contraction amino acids pathways to cause pancreatic
 gastric emptying secretion
 sphincter of Oddi
relaxation
Secretin S cells  pancreatic HCO  by acid, fatty  HCO neutralizes gastric
–
–
3
3
(duodenum) secretion acids in lumen acid in duodenum, allowing
 gastric acid secretion of duodenum pancreatic enzymes to
 bile secretion function
Glucose- K cells Exocrine:  by fatty acids, Also called gastric inhibitory
dependent (duodenum,  gastric H secretion amino acids, peptide (GIP)
+
insulinotropic jejunum) Endocrine: oral glucose Oral glucose load  insulin
peptide  insulin release compared to IV equivalent
due to GIP secretion
Motilin Small intestine Produces migrating motor  in fasting state Motilin receptor agonists (eg,
complexes (MMCs) erythromycin) are used to
stimulate intestinal peristalsis.
Vasoactive Parasympathetic  intestinal water and  by distention VIPoma—non-α, non-β islet
intestinal ganglia in electrolyte secretion and vagal cell pancreatic tumor that
polypeptide sphincters,  relaxation of intestinal stimulation secretes VIP; associated
gallbladder, smooth muscle and  by adrenergic with Watery Diarrhea,
small intestine sphincters input Hypokalemia, Achlorhydria
(WDHA syndrome)
Nitric oxide  smooth muscle Loss of NO secretion is
relaxation, including implicated in  LES tone of
lower esophageal achalasia
sphincter (LES)
Ghrelin Stomach  appetite (“ghrowlin’  in fasting state  in Prader-Willi syndrome
stomach”)  by food  after gastric bypass surgery

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