Which sphincter is responsible for preventing air from entering the esophagus?

The upper esophageal sphincter (UES) plays a critical role in preventing air from entering the esophagus. This muscular ring is located at the junction of the pharynx and the esophagus. Its primary function is to maintain closure of the esophagus during phases of breathing and swallowing, ensuring that food and liquid can pass safely from the throat to the stomach without allowing air to enter the esophagus. The UES relaxes during swallowing to allow food to pass, but it closes tightly to prevent the aspiration of air.

The lower esophageal sphincter (LES), on the other hand, is responsible for preventing the backflow of stomach contents into the esophagus, not addressing air passage. The pyloric sphincter regulates the passage of partially digested food from the stomach to the small intestine and is not involved with air management in the esophagus. Similarly, the pharyngoesophageal sphincter is not a recognized term in the discussion of esophageal anatomy or function related to air prevention.

Understanding the specific roles of each sphincter is essential, particularly in the context of swallowing mechanics and the maintenance of esophageal health.