Chymotrypsin is an enzyme produced in the body that aids in the digestion of food by breaking down proteins. It is made in the small intestine, by complex chemical reactions, from chymotrysinogen. This, together with other digestive substances, is secreted by the pancreas through the pancreatic duct into the duodenum, which lies between the stomach and the small intestine. The secretion is controlled partly by the vagus nerve and partly by hormones, which are released automatically when food enters the duodenum. See also trypsin.