Release of cholecystokinin is stimulated by the presence of peptides, amino acids, or fatty acids in the small intestine. Cholecystokinin acts on the pancreas to stimulate secretion of pancreatic enzymes that aid in the digestion of these compounds. Gastrin secretion is stimulated by the presence of peptides or amino acids in the lumen of the stomach, and produces an increase in gastric H+ secretion. Motilin is a hormone that regulates the migrating myoelectric complex, a series of contractions that occur during fasting, clearing the stomach and small intestine of any residual food. Secretin secretion is stimulated by the presence of H+ and fatty acids in the duodenum, and causes an increase in pancreatic and biliary HCO3; release and a decrease in gastric H+ release. Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 25. Overview of Gastrointestinal Function & Regulation. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong's Review of Medical Physiology, 24e.