GAST and chronic atrophic gastritis: The concentration of G-17 is related to the number of G cells in the antrum and gastric acid, and there is a feedback pathway that controls gastric acid and pepsin in the gastrin link, and the concentration of G-17 decreases when atrophic gastritis destroys the inhibition of the feedback pathway or the gradual loss of G cells with the aggravation of atrophy and the high gastric acid in the patient [60].