The microvasculature and gastric luminal pH of the forestomach of the rat: a comparison with the glandular stomach.

The microvasculature of the rat forestomach was compared with that of the glandular stomach using scanning electron microscopy of vascular corrosion casts and conventional transmission electron microscopy. The forestomach stratified mucosa is relatively poorly vascularized, having a simple 2 dimensional array of continuous capillaries located subepithelially. This contrasts with the extensive mucosal microvascular network of the glandular stomach, where fenestrated capillaries are closer to adjacent cells. pH measurements were taken at the mid-forestomach luminal surface and midfundic luminal surface of the glandular stomach. The H+ concentration was 200 x lower at the forestomach luminal surface. There was always food within the stomach. The pH of the food bolus, which extended throughout the stomach, reflected the pH of the adjacent mucosa. Because of their microvascular differences, the portal transport of HCO3- purported to protect the glandular mucosa from luminal acidity cannot operate at the forestomach mucosa. We speculate that the low forestomach acidity results from the buffering action of the food bolus and that the anatomically distinct dividing ridge restricts direct access of fundic secretions to the forestomach mucosa.