APA Dictionary of Psychology

n. an erosion of a tissue surface, such as the mucosal lining of the digestive tract. Peptic ulcers, which affect the stomach and duodenum, are associated with increased secretion of hydrochloric acid and pepsin, a digestive enzyme, or increased susceptibility of the lining of the stomach and duodenum to the effects of these substances (see gastroduodenal ulceration). See also dyspepsia.