The gastric mucosal barrier and ulceration.

The gastric mucosal barrier is that property which defends against acid and which impedes diffusion of acid from the lumen into the mucosa. The disappearance of luminal H+ is linearly related to luminal (H+) both in the normal stomach and in stomachs exposed to barrier breakers. The latter invaribaly produce anatomic evidence of surface cellular injury. Strong direct evidence for back diffusion of luminal H+ derives from the recent demonstration of a highly significant correlation between the disappearance of luminal H+ and the pH of the lamina propria measured by an implanted microelectrode. The permeabilities of the antrum and fundus to H+ differ from each other in the same species and in different species. Gastric ulceration does not occur in the absence of luminal acid and is not dependent upon the absolute loss of H+ from the luminal solution. Mucosal ischemia induced by hemorrhage reduces tolerance against ulceration as does inhibition of acid secretion, acidification of the tissue caused by absence of nutrient bicarbonate, inhibition of carbonic anhydrase, and blockade of anion exchange by SITS. A tentative schema is proposed by which defense against luminal acid is accomplished in gastric mucosa.