Rugae are folds or ridges found in various organs of the body, most notably in the stomach and the mucosal surface of the vagina. In the stomach, rugae are located on the inner lining and can be seen when the stomach is empty. They are made of mucosal tissue that allows the stomach to expand when it is filled with food.
The primary function of rugae is to facilitate the stretching of the stomach as it fills with food. When you eat, the stomach expands, and the rugae unfold, allowing for increased volume without a significant increase in pressure. This helps the stomach to accommodate more food and aids in the digestion process. Additionally, these folds increase the surface area available for the absorption of nutrients and play a role in the production of gastric juices required for digestion.