Digestion In The Intestines

On entering the duodenum, the acid chyme from the stomach meets three secretions, all alkaline in reaction, namely, the pancreatic juice, the bile, and the intestinal juice.

The hydrochloric acid of the stomach is indirectly responsible for the flow of the pancreatic juice, for this begins only after acid food has entered the duodenum. The pancreatic juice contains an enzyme capable of digesting protein only after it has come into contact with the intestinal juice. This enzyme is then called trypsin, and the changes which it produces in protein are similar to those produced by pepsin; it acts, however, in an alkaline medium.

The products of tryptic digestion are therefore alkali protein, proteoses (albumoses) and peptones.

The bile plays no significant part in protein digestion, except as it helps to neutralize the chyme.

The intestinal juice contains an enzyme called erepsin, which completes the digestion of protein, breaking down the proteoses and peptones formed by pepsin and trypsin into still less complex compounds called amino acids. These are the "end-products" of protein digestion. The digestive process can go no farther. There are no enzymes acting on proteins in the large intestines.

Summary

The chemical changes in protein during the process of digestion are shown in the following table: