Process of dissolving and chemically converting food for absorption by cells.
In the mouth, food is chewed, mixed with saliva , which begins to break down starches, and kneaded by the tongue into a ball for swallowing. acid and enzyme s, which further break it down. The mixture, called chyme , enters the duodenum, the first part of the small intestine. Bile from the liver breaks up {{link=fat">fat globules. Enzymes from the pancreas and intestinal glands act on specific molecules, breaking carbohydrate s down into simple sugar s, protein s into amino acid s, and fats into glycerol and fatty acid s. These products are absorbed by the bloodstream. Indigestible substances, such as fibre , pass into the large intestine, where water and ion s are reabsorbed and feces held for excretion .