Chief cells release pepsinogen rather than pepsin. What converts pepsinogen into pepsin?

1. Pepsinogen is the inactive proenzyme form of pepsin, released by chief cells in the gastric glands. 2. Releasing the enzyme inactive protects the gland cells from being digested by their own product. 3. Hydrochloric acid, made by neighbouring parietal cells, is what converts pepsinogen into active pepsin. 4. This is why gastrin raises acid output when protein arrives: no acid means no working pepsin. 5. Intrinsic factor also comes from parietal cells, but its job is vitamin B12 absorption in the ileum. 6. Alkaline mucus protects the stomach lining and would raise the pH rather than activate anything. 7. Enteropeptidase is a brush border enzyme of the small intestine and activates trypsinogen, not pepsinogen. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 23 "The Digestive System", section 23.4 The Stomach_