Rugae

Composition
Rugae is a term used 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 (gastric rugae).

Function
The function of the rugae is to allow the stomach, or other tissue, to expand when needed. When the stomach is not full, the rugae are folds in the tissue. However, as the stomach fills it expands by unfolding the rugae. Upon emptying, the reformation of the rugae causes the stomach to recede to its former size.

Location
Rugae can appear in the following locations in humans:
 * Wrinkles of the scrotum
 * Hard palate immediately behind the upper anterior teeth
 * Inside the urinary bladder
 * Vagina
 * Gallbladder
 * Inside the stomach

Difference between rugae and plicae
Rugae are only evident when an organ or tissue is deflated or relaxed. For example, rugae are evident within the stomach when it is deflated. However, when the stomach distends, the rugae unfold to allow for the increase in volume. On the other hand, plicae remain folded regardless of distension as is evident within the plicae of the small intestine walls.