Mechanical digestion involves chewing and breaking down food with teeth, while chemical digestion involves the breaking down of food by enzymes and acids in the digestive system. Mechanical digestion mainly occurs directly after ingestion of food, while chemical digestion occurs primarily in the stomach and intestines.
The main form of mechanical digestion is called mastication, in which the teeth manually break down food so that it can be swallowed. The food is then broken down by hydrolysis, a chemical process involving water and enzymes. After hydrolysis, food is then further digested in the stomach after being mixed with stomach acid by stomach contractions called peristalsis, which is a form of mechanical digestion. Once the food is properly broken down, nutrients can be provided to the body from the intestines, while any undigested food is removed from the body as waste.