Current concepts of gastroduodenal mucosal protection.

Mucosal protection against luminal acid and pepsin and recovery from acute damage in the upper gastrointestinal tract depends upon a number of interrelated mechanisms. The thin adherent mucus gel layer protects against shear and luminal pepsin and provides a mixing barrier for surface neutralization of H+ by HCO3- secreted from the underlying epithelia. Gastric HCO3- transport amounts to 2-10% of maximum H+ rate and involves a Cl- exchange mechanism. The rate of duodenal HCO3- transport is some 5-fold greater and both Cl- exchange and transcellular secretion of HCO3- occur. Blood flow ensures adequate oxygenation, provides a pool of HCO3- and maintains mucosal acid-base balance. Gastroduodenal mucosa has a high proliferative rate and in the stomach, the process of continual cell replacement is augmented by restitution of epithelial integrity following acute damage.