After a fatty meal, which gastrointestinal hormone is primarily responsible for gallbladder contraction and pancreatic enzyme secretion, and where are the neurons/cells that release it located?

• A Cholecystokinin (CCK), released from I cells in the duodenal and jejunal mucosa in response to fat and protein in the duodenum; CCK acts via CCK-A receptors on gallbladder smooth muscle (contraction) and acinar cells (enzyme secretion) ✓
• B Secretin, released from S cells in the duodenum in response to fat; secretin acts on ductal cells and gallbladder smooth muscle to produce both bile ejection and fluid secretion
• C Gastrin, released from G cells in the gastric antrum in response to fat entering the duodenum; gastrin stimulates pancreatic enzyme secretion via CCK2 receptors on acinar cells
• D Motilin, released from M cells in the small intestine in response to fat; motilin triggers the migrating motor complex phase III and gallbladder contraction simultaneously

Explanation

CCK is released from I cells located in the duodenal and jejunal mucosa primarily in response to fat (particularly long-chain fatty acids and monoglycerides) and protein (peptides and amino acids) in the duodenum. CCK acts on CCK-A (CCK1) receptors on gallbladder smooth muscle to cause contraction and bile ejection, and on pancreatic acinar cells to stimulate secretion of digestive enzymes (lipase, amylase, proteases). CCK also relaxes the sphincter of Oddi and augments secretin-stimulated bicarbonate secretion. Secretin (from S cells) primarily stimulates pancreatic ductal bicarbonate and water secretion, not enzyme secretion. Motilin triggers phase III MMC (interdigestive), not postprandial gallbladder contraction.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.