Cholecystokinin (CCK), secreted into the blood by enteroendocrine I-cells of the proximal small intestine and by enteric nerves in the ileum and colon, principally stimulates secretion of pancreatic juice and enzymes into the duodenum. It also stimulates gallbladder contraction, which facilitates the release of bile into the duodenum, and to a limited extent, it inhibits gastric emptying and motility. Cholecystokinin also stimulates the release of glucagon by the pancreas. Further, the hormone is found in neurons in the brain, where it influences the perception of appetite, among other processes.

Advanced Nutrition and Human Metabolism By Sareen S. Gropper, Jack L. Smith, Page no: 57.