What hormone primarily triggers gallbladder contraction and bile release into the duodenum?

• A. Cholecystokinin (CCK)
• B. Secretin
• C. Gastrin
• D. Motilin

Answer: (A)

Cholecystokinin (CCK) is released when fatty or protein-rich chyme enters the small intestine. It acts on the gallbladder to cause contraction and also relaxes the sphincter of Oddi, allowing bile to flow into the duodenum. This coordinated action is why CCK is the primary trigger for gallbladder contraction and bile release.

Secretin mainly stimulates the pancreas and the liver to secrete bicarbonate-rich fluids, helping neutralize stomach acid, but it doesn’t drive gallbladder contraction. Gastrin mainly increases gastric acid secretion in the stomach and has little direct effect on the gallbladder. Motilin regulates interdigestive motor activity of the gut and is not responsible for triggering bile release.