Salivary amylase is an enzyme that starts the breakdown of starch in the mouth. Gastric glands of the stomach secrete gastric juice, which contains HCl to kill bacteria and denatures proteins, intrinsic factors, and the enzyme pepsin. The chief cells of gastric glands secrete pepsinogen (an inactive form of pepsin).
Pepsin begins the digestion of proteins in the stomach. It breaks down certain peptide bonds between amino acids and thereby, breaks down protein chain into smaller peptide fragments. Pepsin requires a very acidic environment of the stomach (pH 2) and becomes inactive at a higher pH.
