Which statement best describes the normal function of the LES?

• A. It closes off the esophagus from the stomach
• B. It opens to permit air
• C. It remains open at rest to permit reflux
• D. It seals the trachea during swallowing

Answer: (A)

The lower esophageal sphincter acts as a barrier at the junction between the esophagus and stomach, keeping the stomach contents from moving back up into the esophagus. In normal function, it maintains a tonic closure most of the time to prevent reflux, and it relaxes briefly to allow a swallowed bolus to pass into the stomach before resealing.

That’s why describing it as closing off the esophagus from the stomach best captures its essential role. The other ideas aren’t accurate: opening to permit air isn’t the primary job, it isn’t meant to stay open at rest to let reflux occur, and sealing the trachea during swallowing is the job of the epiglottis and airway protection, not the LES.