Gastric epithelium is liable to be attcked by acid and gastric enzymes but it is protected by a thick alkaline mucus that is secreted by the surface epithelium.

protective barrier between the epithelium and the acid and pepsin in the gastric lumen

mucus is heavily glycosylated to protect it from proteolysis by pepsin

mucus layer is also buffered by HCO3 secreted by the epithelial cells that produces a protective pH gradient across the mucus layer