The relationships between chronic gastritis and gastric acid secretion.

Helicobacter pylori is the main cause of chronic gastritis in humans. Autoimmune mechanisms and Helicobacter heilmannii infection are other causes, both of which are of minor significance in a worldwide perspective. Atrophic gastritis is a quite common late consequence of H. pylori gastritis and will develop on a multifactorial basis, but not in all infected persons. The evolution of atrophic gastritis is a slow and gradually worsening process leading to subtypes, in which the antrum and corpus are affected to dissimilar extent and degree. The distal part of the stomach is the site where the atrophic sequelae (atrophic gastritis and intestinal metaplasia) of H. pylori infection occur most often. A minority of cases develop corpus-limited, or corpus-predominant atrophic gastritis. Along with the worsening of atrophic gastritis, inflammation and density of colonization of the mucosa by H. pylori tend to decrease in grade. In general, the degree of gastric mucosal inflammation, acute and chronic, is positively related to the degree of colonization of the mucosa by H. pylori. Acid secretion and local acidity are factors which modulate the ecology and density of colonization of H. pylori in the stomach, and may thus also modulate the evolution of chronic gastritis into topographically dissimilar subtypes. Acid secretion varies among individuals, this variation being perhaps caused by hereditary differences in parietal cell mass, or by differences in the sensitivity of parietal cells to hormonal or neural stimuli. It is hypothesized that in genuine hypersecretors, H. pylori colonization and subsequent gastritis with atrophic and metaplastic sequelae may be limited to the antrum, while in hyposecretors gastritis predominates in the corpus. In the latter, atrophic gastritis in the corpus then leads to further impairment of acid output. In these cases, H. pylori infection and gastritis may, finally, heal in the antrum, resulting in hypochlorhydria and atrophic gastritis that is limited to, or predominant in the corpus.