Pepsin is a digestive enzyme that breaks down protein. Pepsin is secreted in an inactive form, or zymogen, which is activated by hydrochloric acid and pepsinogen to form the active enzyme pepsin. Pepsin is secreted in an inactive form because it would digest the stomach itself if it were not.
Pepsinogen is a precursor of pepsin, which is the active enzyme that digests proteins in the stomach. Pepsinogen is stored within cells of the mucosa (inner lining) of the stomach for release into its lumen (interior cavity) when needed. Inactive pepsinogen can be activated by acid and converted into its active form, pepsin. Pepsinogen is also secreted from cells lining the duodenum, where it can activate to form pepsin before reaching the small intestine where most protein digestion takes place.
In mammals, gastrointestinal mucosal cells secrete both pepsinogen and trypsinogen into the lumen of their respective organs. Trypsinogen activates to trypsin in response to enteropeptidase present on brush border membranes of intestinal epithelial cells; this process also occurs during pancreas development as well.
Last modified: November 6, 2022