The stomach walls secrete gastric juice which contains three substances: Hydrochloric acid, pepsin enzyme and mucus.

Functions:

(a) Hydrochloric acid kills the germs. It makes acidic medium inside the stomach which is necessary for pepsin enzymes to work.

(b) The enzyme pepsin does partial digestion of protein.

(c) The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid.