Intestinal juice (succus entericus) refers to the clear to pale yellow watery secretions from the glands lining the small intestine walls. Secretion is stimulated by the mechanical pressure of partly digested food in the intestine.

Its function is to complete the process begun by pancreatic juice; the enzyme trypsin exists in pancreatic juice in the inactive form trypsinogen, it is activated by the intestinal enterokinase in intestinal juice. Trypsin can then activate other protease enzymes and catalyze the reaction pro-colipase --> colipase. Colipase is necessary, along with Bile Salts, to enable Lipase function.

Intestinal juice also contains hormones, digestive enzymes, mucus, substances(sodium hydrogencarbonate) to neutralize hydrochloric acid coming from the stomach and erepsin which further digests polypeptides into amino acids, completing protein digestion.

Digestive system