Gastric pits. Coloured scanning electron micrograph (SEM) of the surface of the gastric (stomach) mucosa showing gastric pits. The stomach is a muscular sac involved in storage and digestion of food. Here, the inner mucosa layer of the pyloric (intestine end) region of the stomach, is shown. The layer is composed of long glands which make and secrete gastric juice containing acid and enzymes. These glands open into the stomach lumen through gastric pits (large dark holes). Lining the pits and covering the mucosa surface are mucus-secreting cells (mauve). Mucus protects the mucosa from self-digestion from its juices. Magnification: x135 at 6x7cm size. Magnification: x500 at 10x8 inch size.