<P> Cholecystokinin (CCK or CCK - PZ; from Greek chole, "bile"; cysto, "sac"; kinin, "move"; hence, move the bile - sac (gallbladder)) is a peptide hormone of the gastrointestinal system responsible for stimulating the digestion of fat and protein . Cholecystokinin, previously called pancreozymin, is synthesized and secreted by enteroendocrine cells in the duodenum, the first segment of the small intestine . Its presence causes the release of digestive enzymes and bile from the pancreas and gallbladder, respectively, and also acts as a hunger suppressant . </P> <P> The existence of CCK was first suggested in 1905 by the British physiologist Joy Simcha Cohen . It is a member of the gastrin / cholecystokinin family of peptide hormones and is very similar in structure to gastrin, another gastrointestinal hormone . CCK and gastrin share the same five C - terminal amino acids . CCK is composed of varying numbers of amino acids depending on post-translational modification of the 150 - amino acid precursor, preprocholecystokinin . Thus, the CCK peptide hormone exists in several forms, each identified by the number of amino acids it contains, e.g., CCK58, CCK33, CCK22 and CCK8 . CCK58 assumes a helix - turn - helix configuration . Biological activity resides in the C - terminus of the peptide . Most CCK peptides have a sulfate - group attached to a tyrosine located seven residues from the C - terminus . This modification is crucial for the ability of CCK to activate the cholecystokinin A receptor . Nonsulfated CCK peptides also occur, which consequently cannot activate the CCK - A receptor . </P> <P> CCK plays important physiologic roles both as a neuropeptide in the central nervous system and as a peptide hormone in the gut . It participates in a number of physiological processes such as digestion, satiety and anxiety . </P> <P> CCK is synthesized and released by enteroendocrine cells in the mucosal lining of the small intestine (mostly in the duodenum and jejunum), called I cells, neurons of the enteric nervous system, and neurons in the brain . It is released rapidly into the circulation in response to a meal . The greatest stimulator of CCK release is the presence of fatty acid s and / or certain amino acids in the chyme entering the duodenum . In addition, release of CCK is stimulated by monitor peptide (released by pancreatic acinar cells), CCK - releasing protein (via paracrine signalling mediated by enterocytes in the gastric and intestinal mucosa), and acetylcholine (released by the parasympathetic nerve fibers of the vagus nerve). </P>

Cck stimulates the release of bile and lipase into the duodenum