I cells secrete

-Cholecystokinin (CCK) is secreted by cells in the mucosa of the upper small intestine. It has a plethora of actions in the gastrointestinal system, but the most impoant appear to be the stimulation of pancreatic enzyme secretion, the contraction of the gallbladder (the action for which it was named), and relaxation of the sphincter of Oddi, which allows both bile and pancreatic juice to flow into the intestinal lumen. -Gastrin is produced by cells called G cells in the antral poion of the gastric mucosa -Secretin is secreted by S cells that are located deep in the glands of the mucosa of the upper poion of the small intestine -Motilin is secreted by enterochromaffin cells Reference ; GANONG'S REVIEW OF MEDICAL PHYSIOLOGY 23RD EDITION Pg 745,746,747