During the intestinal phase of digestion, cholecystokinin (CCK) is released. Which cells secrete CCK, and what are its three main effects on gastrointestinal function?

• A I-cells of the proximal small intestine (duodenum/jejunum); stimulates gallbladder contraction, increases pancreatic enzyme secretion, and inhibits gastric emptying (via relaxation of pyloric sphincter and duodenal feedback) ✓
• B S-cells of the duodenum; stimulates pancreatic bicarbonate secretion, contracts the sphincter of Oddi, and increases gastric acid
• C I-cells; stimulates gallbladder contraction, inhibits pancreatic enzyme secretion (negative feedback), and accelerates gastric emptying
• D K-cells of the duodenum; stimulates insulin release, contracts the gallbladder, and increases colonic motility

Explanation

CCK is secreted by I-cells located predominantly in the duodenal and jejunal mucosa in response to luminal fat (long-chain fatty acids) and protein digestion products (peptides and amino acids). Its three classical effects are: (1) gallbladder contraction (via CCK1 receptors on gallbladder smooth muscle) to release bile into the duodenum; (2) stimulation of pancreatic acinar cells to secrete digestive enzymes (lipase, amylase, proteases); and (3) inhibition of gastric emptying by relaxing the pyloric sphincter and stimulating duodenal smooth muscle to slow gastric outflow, allowing adequate time for digestion. CCK also contracts the sphincter of Oddi (via CCK1 receptors) to coordinate bile and pancreatic juice entry. Option B describes secretin's actions (S-cells, bicarbonate, not enzyme). Option C incorrectly states CCK inhibits enzyme secretion. Option D describes GIP from K-cells.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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Written and medically reviewed by the StethoPrep medical team.