Mosby Radiography Practice Test

Rugae are large folds in the stomach lining that allow the organ to expand as it fills, providing more surface area when empty and flattening as it stretches. This distinctive feature is specific to the stomach; the esophagus has a smooth, non-folded lining, the small intestine shows circular folds with villi for absorption rather than rugae, and the large intestine has haustra from muscular tone rather than rugae. So these folds identify the stomach lining.