<prompt> Mainly cholecystokinin is secreted by:DuodenumPancreasGallbladderIleum  <response>: Release of cholecystokinin CCK from the duodenum and proximal jejunum is triggered by long-chain fatty acids, ceain essential amino acids tryptophan, phenylalanine, valine, methionine, and gastric acid itself. CCK evokes an enzyme-rich secretion from acinar cells in the pancreas. 