Stomach lining. Coloured light micrograph (LM) of the stomach. The lumen is at top (white). The surface of the mucosa consists of simple columnar cells that secrete mucus. The mucus protects the stomach lining from digestive acids and enzymes that act on food in the stomach. Beneath the columnar cells are gastric pits, the glands that make the acids and enzymes needed to digest food. Magnification: x100 when printed 10cm wide