The key difference between the upper esophageal sphincter (UES) and the lower esophageal sphincter (LES) lies in their location and function within the swallowing process.
Upper Esophageal Sphincter (UES)
The UES is located at the very top of the esophagus, where it connects to the pharynx (throat). It's primarily responsible for preventing air from entering the esophagus during breathing and protecting the airway from the contents of the esophagus. The UES is usually closed except during swallowing.
- Function: Prevents air entry into esophagus; protects airway.
- State: Normally closed, opens only during swallowing.
Lower Esophageal Sphincter (LES)
The LES is located at the bottom of the esophagus, where it meets the stomach. Its primary role is to prevent the acidic contents of the stomach from refluxing (flowing back) into the esophagus. This prevents heartburn and esophageal damage. The LES relaxes to allow food to pass into the stomach.
- Function: Prevents stomach acid reflux into the esophagus.
- State: Normally closed; relaxes to allow food passage into the stomach.
As the reference states, "With normal swallowing, the UES opens only when a person is swallowing food and otherwise remains closed. Peristaltic contractions then move the food down the esophagus. At the bottom of the esophagus, the LES opens to allow food to empty into the stomach." This highlights the coordinated opening and closing of these sphincters during the act of swallowing.
