It is a hormone secreted by the I-cells or inclusion cells of the upper small intestine in response to fat, protein, and some non-nutrients.
It stimulates the secretion of pancreatic enzymes and bile juice.
The physiological actions of CCK include stimulation of pancreatic secretion and gallbladder contraction, regulation of gastric emptying, and induction of satiety. CCK can function as either a hormone or a neuropeptide.
CCK is produced by two separate cell types, endocrine cells of the small intestine and various neurons in the gastrointestinal tract and central nervous system.