Cholecystokinin, commonly abbreviated as CCK, is the primary hormone responsible for stimulating the gallbladder to release bile into the small intestine during digestion. Produced primarily by enteroendocrine cells in the duodenum and jejunum, CCK acts as a chemical messenger that coordinates fat digestion, nutrient absorption, and gastrointestinal motility. When fatty or protein-rich foods enter the small intestine, these specialized cells release CCK into the bloodstream, where it travels to the gallbladder and biliary tree, prompting contraction and bile secretion. This process not only emulsifies fats for enzymatic breakdown but also signals the pancreas to release digestive enzymes, making CCK a cornerstone of postprandial gastrointestinal function.
The identity of the hormone that stimulates the gallbladder to release bile is deeply rooted in its receptor-mediated mechanism. CCK binds to CCK-A receptors located on the smooth muscle of the gallbladder and the sphincter of Oddi. This binding triggers a cascade of intracellular signaling, primarily involving phosphoinositide hydrolysis and calcium mobilization, which leads to gallbladder contraction and relaxation of the sphincter, allowing bile to flow into the duodenum. The release is further modulated by neural input from the vagus nerve and local gastrointestinal peptides, ensuring a tightly regulated response to the composition of the incoming chyme.
Beyond its gallbladder-stimulating role, cholecystokinin influences multiple facets of digestion. It slows gastric emptying, promoting a feeling of satiety and reducing overeating. It also stimulates the secretion of bicarbonate from the pancreas and liver
