Endoscope image of an ulcer of the anterior wall of the duodenal bulb, the upper part of the duodenum. The base of the cratered ulcer (oval, yellow-white) appears to the left of the lumen at the centre of the image. The cause of duodenal ulcers is obscure. The destruction of the mucous membrane & underlying muscle layers in susceptible individuals is due to the action of acid & pepsin released from the stomach. Hypersecretion of gastric acid is not believed to be the only factor; cigarette smoking & aspirin-type drugs are also implicated. Healing is promoted by drugs that block the secretion of gastric acid. Duodenal & stomach ulcers are sometimes called peptic ulcers.