Which parts of the gut are the primary sites for secretion of cholecystokinin and secretin?

• A. Stomach and duodenum
• B. Duodenum and Jejunum
• C. Ileum and colon
• D. Jejunum and Ileum

Answer: (B)

Cholecystokinin and secretin are produced by enteroendocrine cells in the proximal small intestine. Secretin is released by S cells in the duodenum in response to acidic chyme, helping to neutralize stomach acid by stimulating pancreatic bicarbonate. Cholecystokinin is released by I cells in the duodenum and the proximal jejunum in response to fats and amino acids, promoting gallbladder contraction and pancreatic enzyme secretion. Since the duodenum and nearby jejunum are where these hormones are primarily secreted, selecting the duodenum and jejunum captures the main sites for both hormones. The ileum and colon do not serve as primary sources for these secretions, and the stomach isn’t the main source for either of these hormones.