英语时差：食物是如何消化的？2

At night when there’s no food in your stomach, the protease is deactivated so it stops working. Unfortunately, disease, alcohol, and some drugs can override the enzyme that is supposed to be controlling the protease. When that happens, the protease begins to digest the stomach wall and ulcers develop. So, in a healthy person, the body builds its digestive enzymes with what amounts to an on/off switch and then builds a second enzyme especially designed to operate the switch. The digestive system also protects itself by being one of the fast growing tissues in the body, constantly discarding old cells and reproducing new ones. So some of it does get digested, but there’s always more to take its place.