Answer
The delicate lining of the stomach consists of an layer of epithelial cells. During the process of digestion the glands of the stomach produce a strong acid ( pH 1.5-2-5) , and proteolytic enzyme; In addition the mechanical mixing motion of the stomach is quite vigorous especially towards the region of the antrum. These factors expose the lining of the stomach to daily tissue damage. . Yet the lining of the stomach is protected and it carries usually carries out its functions several times a day for many decades usually without injury. This is possible because the tissues of the walls of the stomach are protected by three main physiological mechanisms; the alkaline secretion of the mucous lining; the tight junctions of the
columnar epithelial cells; the rapid replacement of lost surface cells by the mitotic activity basal cells in the gastric pits
Work Step by Step
Strong hydrochloric acid is destructive to organic material, but the the acidity of the chyme in the stomach is counteracted by the alkaline secretions of the mucous coat cells of the stomach walls
Pepsin is a protease, and this enzyme would be expected to digest the cells of the stomach walls. However, the enzyme is secreted in inactive form or zymogen ( pepsinogen), and only becomes active after being acted upon by HCL. When the pepsin is formed the food ( chyme) mixes with it and so it does not have free access to the stomach wall. The chyme is acid, nevertheless, and some damage is sustained by the epithelial layer. Consequently, epithelial cells live for only about 5 days; the dead cells sloughed off and are passed out with the chyme and replaced by new cells produced by mitosis of cells in gastric pits. Damage to the cells and fibers of the connective tissue of the stomach wall would be a more serious problem. Therefore, the the columnar epithelial cells of the surface layer have tight junctions that prevent leakage of acidic chyme or HCL into the submucosa.
