Defensive barrier of gastric and duodenal mucosa mucus barrier mucosal barrier physical defense chemical counteraction quick refreshment of epithelial cell abundant circulation of blood HCO, nutrition factor: pgelege intercellular tight junction abundant submucosal blood vessel HCO, counteracts h+Defensive barrier of gastric and duodenal mucosa mucus barrier physical defense chemical counteraction mucosal barrier quick refreshment of epithelial cell abundant circulation of blood nutrition factor: PGE1,EGF intercellular tight junction abundant submucosal blood vessel HCO3 - counteracts H+