What is the function of the lower esophageal sphincter during swallowing?

• A. The lower esophageal sphincter contracts during swallowing, preventing entry.
• B. The lower esophageal sphincter remains closed at all times.
• C. The lower esophageal sphincter relaxes during swallowing to allow food to enter the stomach.
• D. The lower esophageal sphincter actively pumps chyme into the stomach.

Answer: (C)

During swallowing, the lower esophageal sphincter relaxes to open and let the swallowed bolus pass from the esophagus into the stomach. Normally this sphincter stays closed to prevent reflux, so it must open briefly as a swallow progresses and esophageal peristalsis moves the food downward. Once the bolus has entered the stomach, the sphincter tightens again to restore the barrier. It doesn’t actively pump chyme; instead, chyme movement is accomplished by stomach mixing and peristaltic waves, with the sphincter providing a gate that opens only as needed for entry.