Barrier function of gastric mucus.

A viscoelastic mucus gel layer covers the gastric mucosa in a continuous sheet. The functions of the mucus gel have been one of the least studied aspects of gastric barrier function. Although the role of gastric mucus in providing physical protection against ingested particles, and preventing contact between digestive enzymes such as pepsin and the underlying mucosa is generally accepted, the barrier role function of gastric mucus with regard to luminal acid is still conjectural. The modest proton diffusion barrier that mucus provides is negligible in relation to the overall barrier properties of the gastric mucosa; nevertheless, stabilization of unstirred layers and damping of rapid shifts in luminal pH are potentially important functions. Associative studies have suggested a possible role of a hydrophobic barrier in strengthening the barrier functions of mucus. One of the most actively investigated areas of mucus function in recent times has been the mechanism by which secreted acid traverses the gel. Although compelling and complementary data obtained in vivo and in vitro have been consistent with secretion of acid under pressure, creating temporary viscous fingers through the gel, recent evidence obtained with in vivo confocal microscopy suggests that secreted acid diffuses through the gel. Since Helicobacter pylori exists solely in the juxtamucosal portion of the gastric mucus gel, detailed knowledge concerning the pH microenvironment in which the organism thrives is important in understanding the pathophysiology of peptic ulcer disease and related conditions.