Lower esophageal sphincter (LES)

The lower esophageal sphincter (LES) is a ring of muscle that forms a valve at the lower end of the esophagus, where it joins the stomach.

The LES remains closed except during swallowing, when it allows food to pass from the esophagus into the stomach. When the LES is closed, it prevents the backflow (reflux) of stomach acid into the esophagus. If the LES does not close tightly enough, stomach acid backs up into the esophagus, causing heartburn. A weak lower esophageal sphincter is a major cause of gastroesophageal reflux disease (GERD).

Last Updated: March 31, 2008

Author: Monica Rhodes

Medical Review: Kathleen Romito, MD - Family Medicine & Jerome B. Simon, MD, FRCPC, FACP - Gastroenterology

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