Stomach wall. Light micrograph of a section through the stomach wall. At top (white) is the stomach lumen. The upper layer (pink) is the mucosa. It is folded to increase the surface area. This layer contains the glands producing gastric juice. At the very edge of this layer (dark pink) are the gastric pits where the gastric juice is secreted into the stomach lumen. The layer below and in the core of the mucosal folds (orange) is the submucosa containing blood vessels. The muscular layers beneath the submucosa are seen most clearly at bottom left. There is an inner circular layer (above) followed by an outer longitudinal layer (below). Magnification unknown.