Which of the following statements about the LES is true?

• A. The LES opens during swallowing
• B. The LES closes off the esophagus from the stomach
• C. The LES relaxes during sleep
• D. The LES remains contracted at all times

Answer: (B)

The lower esophageal sphincter serves as a barrier at the junction where the esophagus meets the stomach, staying tightly closed to prevent stomach contents from refluxing upward. The true statement highlights this barrier function: it closes off the esophagus from the stomach. When a swallow begins, the LES undergoes a brief, transient relaxation to let the food bolus pass into the stomach, then it tightens again to reestablish the barrier. It is not correct to say it remains contracted at all times, nor to say it stays open during swallowing; the opening is a controlled, temporary relaxation, not a permanent state. While LES tone can vary with sleep, the essential point to grasp is its role as a barrier that relaxes briefly to allow swallowing and then seals again.