The hormones of the digestive system include gastrin, secretin, and cholecystokinin (CCK. Gastrin stimlates the stomach to secrete gastric juice. Secretin stimulates the exocrine portion of the pancreas to secrete bicarbonate into the pancreatic fluid (thus neutralizing the acidity of the intestinal contents). Cholecystokinin causes the gall bladder to contract, secreting bile, and it also causes the pancreas to increase the level digestive enzymes in the pancreatic fluid.