This peptide hormone induces gall bladder contraction and the release of pancreatic enzymes in the gut. Its function in the brain is not clear. Binding to CCK-A receptors stimulates amylase release from the pancreas, binding to CCK-B receptors stimulates gastric acid secretion. Binds to CCK-A receptors in the pancreas and CCK-B receptors in the brain. Expressed and secreted by discrete enteroendocrine cells that reside as single cells scattered among enterocytes in the mucosa of the small intestine. Released into the blood following ingestion of a meal. The precursor is cleaved by proteases to produce a number of active cholecystokinins. Belongs to the gastrin/cholecystokinin family.