The gastric rugae may be seen during esophagogastroduodenoscopy

Esophagogastroduodenoscopy

For other expansions of the initialism "OGD", see the disambiguation page.In medicine , esophagogastroduodenoscopy is a diagnostic endoscopic procedure that visualizes the upper part of the gastrointestinal tract up to the duodenum...

or in radiological studies. They provide the stomach with increased surface area for food. When food enters the stomach, these rugae fold and become stretched in. The purpose is to allow it to expand. This therefore allows expansion in volume of the stomach without increased pressure.