Rugae is a term use in anatomy that refers to a series of ridges produced by folding of the wall of an organ. Most commonly the term is applied to the internal surface of the stomach. The stomach rugae may be seen during esophagogastroduodenoscopy or in radiological studies. They provide the stomach with a lower amount of surface area for food. When food enters the stomach, these rugae fold and become stretched in. The purpose is to allow it to expand.This therefore allows expansion in volume of the stomach without increased pressure.