Digestion involves two distinct parts. The first is mechanical digestion by chewing, grinding, churning and mixing that takes place in the mouth and the stomach. The second part of digestion is the chemical digestion that uses enzymes, bile acids etc. in order to break down food material into a form that can then be absorbed, then assimilated into the tissues of the body. Chemical digestion occurs in the small intestine (and, to a lesser extent, also in some other part of the gastrointestinal tract.