1. Mechanical digestion of food
(i) Crushed red food passes through the cardiac orifice into the stomach. At this time cardiac and pyloric sphincter openings are closed.
(ii) Peristalsis waves are initiated in the stomach. The peristalsis wave begins at the fundus of the stomach and ends at the pylori.
(iii) Peristalsis occurs due to contraction of circular muscles and longitudinal muscles. At the top of the esophagus are the circular muscles and at the bottom are the longitudinal muscles.
(iv) Cardiac sphincter dilates when food reaches end of esophagus and food is expelled into stomach.
(v) Gastric juice and hydrochloric acid mix with food inside the stomach to form chyme.
(vi) HCl secreted from the stomach destroys food microbes. Creates an acidic environment for digestion.
2. Chemical digestion of food
(i) Inactive pepsinogen is converted to active pepsin under the influence of HCl. Pepsin breaks down proteins into proteases and peptones.
(ii) Gelatinase enzyme breaks down gelatin to produce peptones and polypeptides.
(iii) Lipase enzyme breaks down lipids to produce fatty acids, glycerol and monoglycerides.