Which hormone relaxes the sphincter of Oddi to promote bile release into the duodenum?

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

Answer: (C)

Bile release into the duodenum is driven by hormones that coordinate gallbladder activity with the opening of the bile duct. When fatty or protein-rich chyme enters the small intestine, the I cells release cholecystokinin. This hormone has a dual action: it makes the gallbladder contract to push bile forward and, crucially, relaxes the sphincter of Oddi, removing the bottleneck so bile can flow into the duodenum. It also stimulates the pancreas to secrete digestive enzymes, supporting fat digestion. Other hormones like secretin mainly increase pancreatic bicarbonate, gastrin increases gastric acid, and motilin boosts GI motility; none primarily control the sphincter of Oddi. So, the hormone that relaxes the sphincter of Oddi to promote bile release is cholecystokinin.