Stomach lining. Coloured scanning electron micrograph (SEM) of the lining of the stomach, known as the mucosa. This area is in the antrum, a region at the end of the stomach near the opening into the intestine. The surface consists of simple columnar cells that secrete mucus. The mucus protects the stomach lining from digestive acids and other chemicals that act on food in the stomach. The gastric wall is thrown into folds, all of which are folded again on a smaller scale. Cells in the antrum do not secrete digestive acids. Magnification: x320 when printed 10 centimetres wide.