THE GASTRIC MUCOSAL BARRIER
The stomach is well protected from the damaging effects of gastric acid, pepsin, bile acids, and other digestive enzymes by a complex of physical and chemical components known as the gastric mucosal barrier (GMB).The most superficial component of the GMB is a thick mucus- bicarbonate layer secreted by gastric epithelial cells.
Surface mucus acts as a lubricant to prevent mechanical damage. An underlying glycoprotein gel adheres to the mucosa and traps bicarbonate secreted by epithelial cells to maintain surface mucosal pH above 6. This layer provides an electricalchemical barrier to impede diffusion of luminal acid and pepsin into the epithelium. Gastric epithelial cells have low permeability to water and ions and have tight intercellular junctions, features that also inhibit diffusion of luminal chemicals into the epithelium. Another important feature of the GMB is the ability of gastric epithelial cells to continually and rapidly repair injured cells, a characteristic known as epithelial restitution. In the event of superficial mucosal injury, cells at the edge of the damaged area migrate over the defect within a few hours to prevent deeper damage to the mucosa. A dense network of submucosal capillaries supplies oxygen and nutrients to meet the high metabolic demands of mucus and bicarbonate secretion and of rapid cellular renewal. Perhaps the most important component of the GMB is prostaglandin produced by the GI mucosa. Prostaglandin E increases mucus and bicarbonate secretion, regulates mucosal blood flow, stimulates epithelial cell growth, and inhibits acid secretion. The collective effect is to enhance rapid epithelial restitution, to prevent damage to the surface mucosa, and to prevent progression of damage deeper into the submucosa.
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