The stomach walls contain three layers of smooth muscle arranged in longitudinal, circular, and oblique (diagonal) rows. These muscles allow the stomach to squeeze and churn the food during mechanical digestion.

Powerful hydrochloric acid in the stomach helps break down the bolus into a liquid called chyme. A thick mucus layer that lines the stomach walls prevents the stomach from digesting itself. When mucus is limited, an ulcer (erosion of tissue) may form.

Food is digested in the stomach for several hours. During this time, a stomach enzyme called pepsin breaks down most of the protein in the food. Next, the chyme is slowly transported from the pylorus (end portion of the stomach) through a sphincter and into the small intestine where further digestion and nutrient absorption occurs.

additional information:

chyme- a thick semifluid mass of partly digested food that is passed from the stomach into the duodenum, the first section of the small intestine.

pepsin- enzyme produced in the mucosal lining of the stomach that acts to degrade protein. Pepsin is one of three principal protein-degrading, or proteolytic enzymes in the digestive system. During the process of digestion, these enzymes, each of which is particularly effective in severing links between particular types of amino acids, collaborate to break down dietary proteins to their components, i.e., peptides and amino acids, which can be readily absorbed by the intestinal lining.

Pepsin is synthesized in an inactive form by the stomach lining; hydrochloric acid, also produced by the gastric mucosa, is necessary to convert the inactive enzyme and to maintain the optimum acidity (pH 1–3) for pepsin function. Pepsin and other proteolytic enzymes are used in the laboratory analysis of various proteins; pepsin is also used in the preparation of cheese and other protein-containing foods.

pepsin

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