Complex sentence: Gastrin stimulates the production of gastric acid by parietal cells and, in "H. pylori" colonization responses that increase gastrin, the increase in acid can contribute to the erosion of the mucosa and therefore ulcer formation.
Split into simpler sentences: Gastrin stimulates the production of gastric acid by parietal cells. In "H. pylori" colonization responses to increased gastrin, the increase in acid can contribute to the erosion of the mucosa and therefore ulcer formation.