I - StomachII - PancreasIII - LiverIV - Gall bladderEnzymatic (chemical) digestion of protein begins in the stomach - labelled part I. The stomach lining contains specialized cells called chief cells that secrete pepsinogen, an inactive proenzyme. When this comes into contact with hydrochloric acid (HCl) produced by parietal cells, it is converted into the active enzyme pepsin. Pepsin initiates the chemical breakdown of large protein molecules into smaller chains called polypeptides.
