Gastric acid or the stomach acid is mainly composed of hydrochloric acid, chemically called HCL. The gastric acid also contains potassium chloride and sodium chloride. The acid is produced by the cells that form the lining of the stomach. Some cells in the stomach produce a base called bicarbonate to buffer the acid medium of the stomach. Mucus is also produced by the cells to cover the inner lining of the stomach and prevent the acid damaging the stomach. When the food in the stomach goes to the next level, which is the small intestine, it gets neutralized. This is because the duodenum, the first part of the small intestine produces large amounts of bicarbonate. Gastric Acid and Protein Breakdown: Gastrin is the enzyme that triggers the production of gastric acid in the stomach. It is produced by the inner linings of the stomach; Meanwhile, pepsinogen, an enzyme, is secreted by the gastric chief cells to breakdown the proteins; Hydrochloric acid activates pepsinogen into the enzyme pepsin; Pepsin breaks the bonds that link amino acids in proteins, unfolding the protein structure and revealing the peptide bonds. This process is called proteolysis. Many harmful microbes are killed in this acidic medium.