Which hormone stimulates bicarbonate-rich pancreatic secretions?

• A. Secretin
• B. CCK
• C. Gastrin
• D. Motilin

Answer: (A)

Secretin is the hormone that triggers bicarbonate-rich pancreatic secretions. When acidic chyme enters the duodenum, S cells release secretin, which travels to the pancreas and acts on the ductal cells. Through a cAMP-mediated mechanism, secretin stimulates these cells to secrete a fluid high in bicarbonate, neutralizing the acidic content and providing a suitable pH for digestive enzymes to function.

The other hormones have different primary roles: cholecystokinin mainly stimulates enzyme-rich pancreatic juice release and gallbladder contraction; gastrin mainly increases gastric acid secretion by the stomach; motilin governs migrating motor complexes and gut motility rather than bicarbonate secretion.