CCK; a polypeptide (of 33 residues) hormone liberated by the upper intestinal mucosa on contact with gastric contents -during the intestinal phase of the digestive period (not during a fast). Its secretion is evoked by the presence of fat andprotein digestion products in the duodenum. Stimulates contraction of the gallbladder, relaxation of the sphincter of Oddiand secretion of pancreatic juice. See: sincalide. Syn: pancreozymin.