Where is gastric juice formed and what is in it?

Gastric juice is produced by glands that form the lining of the stomach walls. It includes:

water is a solvent and medium for digestion reactions (90%);
pepsin – an enzyme that breaks down proteins into amino acids;
chloride or hydrochloric acid – activates pepsin; destroys bacteria (0.5%);
lipase – an enzyme that breaks down milk fats into glycerin and fatty acids;
mucin – mucus that protects the walls of the stomach from acid and self-digestion.