Gastric ulcer. Light micrograph of a section of the lining of the stomach showing a gastric ulcer. The ulcer is at upper left (v-shaped), where the protective membrane has been destroyed. Gastric ulcers are caused by the action of acid, pepsin and bile on the stomach lining (mucosa). If the mucosa is compromised due to excess alcohol consumption, stress or certain drugs, the lining is eaten away. Symptoms include vomiting and pain. Most cases clear up with antacid drugs, but if ulcers reoccur or even perforate the stomach, surgery is required. Magnification unknown.