What physiological action is likely triggered by the release of CCK?

• A. Relaxation of muscle in the wall of the gallbladder and relaxation of the hepatopancreatic sphincter
• B. Contraction of muscle in the wall of the gallbladder and relaxation of the hepatopancreatic sphincter
• C. Relaxation of muscle in the wall of the gallbladder and contraction of the hepatopancreatic sphincter
• D. Contraction of muscle in the wall of the gallbladder and contraction of the hepatopancreatic sphincter

Answer: (B)

Cholecystokinin (CCK) is a peptide hormone produced primarily by the cells of the duodenum in response to the presence of fats and proteins in the small intestine. Its primary physiological action includes stimulating the gallbladder to contract, which results in the release of bile into the small intestine. This bile is crucial for the emulsification and digestion of fats.

Additionally, CCK has a role in relaxing the hepatopancreatic sphincter (also known as the sphincter of Oddi), which allows bile and pancreatic juices to flow into the small intestine more freely. By promoting gallbladder contraction while simultaneously causing relaxation of the sphincter, CCK effectively facilitates the digestive process, ensuring that bile can reach the intestines when it's needed for fat digestion.

This understanding underpins why the physiological action associated with the release of CCK is correctly identified as contraction of muscle in the wall of the gallbladder and relaxation of the hepatopancreatic sphincter.