At the opening of your upper esophagus there’s a ring shaped muscle called the upper esophageal sphincter. Your upper esophagus senses when food or liquid is coming towards it. when it gets the signal the sphincter relaxes or opens so that food can enter your esophagus. When there’s no food or liquid it stays closed.
Once the foods inside your esophagus waves of muscular contractions push the food downward. The food passes through your diaphragm and teachers your lower esophagus.
At the opening of your lower esophagus there’s another ring shaped muscle called the lower esophageal sphincter like the upper esophageal sphincter (LES) or (UES). It senses when food or liquid are coming. It relaxes and lets the food pass through to your stomach.