The two phases of digestion are mechanical digestion and chemical digestion, according to Midlands Technical College. Both phases occur in the mouth, stomach and small intestine, but chemical digestion also occurs in the large intestine.
Digestion begins as soon as someone ingests food. Mechanical breakdown starts when the teeth chew food and the tongue mixes food with saliva. Salivary amylase begins chemical digestion by breaking down starch molecules. Once food reaches the stomach, mechanical breakdown continues when strong muscular contractions mix food with gastric juice. At this time, a substance called pepsin starts to break down proteins, reports Midlands Technical College. The food is then propelled into the duodenum, or first part of the small intestine.
The smooth muscle of the small intestine continues the mechanical breakdown of food by mixing the food with digestive juices. Chemical digestion is controlled by brush border enzymes and enzymes carried to the small intestine by the pancreas. At this point, the mechanical breakdown of the food is complete. Any remaining food residue is broken down by the bacteria living in the large intestine. The large intestine also absorbs electrolytes, some vitamins and most of the remaining water, states Midlands Technical College. The waste products of digestion are then stored in the large intestine as feces.