Partially digested food entering the stomach is composed of di and tri saccharides, polypeptides, and lipids. The production of gastric fluid (juice) was introduced, along with the production of hydrochloric acid. The enzyme pepsin secreted was shown to be a protease enzyme, which is activated in an acidic medium. The acid serves a variety of purposes, to activate the enzyme, to help in the dissolution of minerals like calcium, and to aid in the killing of bacteria swallowed with the food. The action of the pepsin on the proteins was shown to speed up the hydrolysis of the polypeptides into di and tri peptides. The stomach contents are becoming the consistency of a mash (chyme) consisting of partially digested carbohydrates, partially digested proteins, and lipids.
The sphincter muscle opens and allows the food to enter the small intestines in controlled amounts.
The action of the intestinal glands and the pancreatic glands was briefly described, the major functions to be discussed.