What is the name and the function of the prominent longitudinal mucosal folds seen in an empty stomach.

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Rugae are the mucosal folds of the stomach that allow it to stretch. In an empty stomach, these longitudinal folds bunch up to form ridges, giving the organ extra length and surface area without a large internal volume. As you eat and the stomach fills, the rugae flatten out, letting the stomach expand to accommodate more content. This expansion is the key function: it enables the stomach to store ingested material and then gradually process it as it empties. The other options mix up structure and function—for example, plicae are folds in the small intestine that increase surface area for absorption, not features of the stomach; microvilli are tiny projections on intestinal absorptive cells, not the stomach’s folds; and mucus is produced by gastric mucous cells rather than the rugae themselves.