Digestion of carbohydrates begins at the mouth when amylase is secreted to catalyze the break down of starch (amylose) to maltose.

The breakdown of proteins begins in the stomach with the secretion of the enzyme pepsin. The stomach assists the break down of protein by secreting acid as well as by initiating powerful muscle contractions which help to mechanically mix the enzymes and food as well as crushing the food into smaller pieces.

After passing into the small intestine, the pH is altered to neutral and enzymes secreted by the pancrease, gall bladder and walls of the small intestines continue the digestive process. The end products of digestion are absorbed by the villi (and their smaller microvilli) and the nutrients pass into the bloodstream.

The indigestible products of digestion pass to the large intestine along with water. It is in the large intestine where the bulk of the water is absorbed into the blood stream. The remaining indegestible matter solidifies and is eventually expelled from the body via the anus.