Which hormone primarily stimulates enzyme-rich pancreatic secretions and gallbladder contraction during a mixed meal?

• A. Gastrin stimulates acid secretion
• B. CCK stimulates enzyme-rich pancreatic secretions and gallbladder contraction
• C. Secretin stimulates bicarbonate-rich pancreatic secretions
• D. Motilin stimulates migrating motor complex

Answer: (B)

When fats and proteins enter the duodenum during a mixed meal, the small intestine releases cholecystokinin. This hormone directly stimulates pancreatic acinar cells to secrete enzyme-rich pancreatic juice (lipases, proteases, amylase) and it also causes the gallbladder to contract, delivering bile into the duodenum. It even relaxes the sphincter of Oddi to let these secretions reach the intestine.

Gastrin mainly increases gastric acid secretion in the stomach, secretin prompts bicarbonate-rich pancreatic secretions to neutralize acid in the duodenum, and motilin drives the migrating motor complex during fasting. The combination of enzyme-rich pancreatic juice and bile release during a meal is primarily driven by cholecystokinin.