What are the folds within the stomach that allow it to expand when full?

The folds within the stomach that enable it to expand when full are known as rugae. Rugae are large, longitudinal folds of the gastric mucosa that allow the stomach to stretch and accommodate varying volumes of food and liquid. When the stomach is empty, these folds are prominent, but as the stomach fills, the rugae become flattened, which allows for expansion without significantly increasing internal pressure.

Villi and microvilli are terms associated with the small intestine; villi are small finger-like projections that increase surface area for absorption, while microvilli are even smaller projections on the epithelial cells of the villi that further enhance absorption. Plicae circulares are also structures found in the small intestine, which are circular folds that serve a similar purpose to villi but are not involved in the stomach's ability to expand. Therefore, rugae specifically relate to the stomach's unique capacity to accommodate its contents.