The structure that controls the passage of food from the esophagus to the stomach is called the lower esophageal sphincter (LES).
The lower esophageal sphincter is a ring of muscle located at the junction between the esophagus and the stomach. Its primary role is to act as a gateway. When food is swallowed, the LES relaxes to allow the food to pass into the stomach. Once the food has entered the stomach, the sphincter tightens again to prevent the stomach contents from flowing back up into the esophagus.
This function is crucial for maintaining proper digestion and preventing conditions such as gastroesophageal reflux disease (GERD), where the acidic contents of the stomach can irritate the esophagus if the sphincter does not close properly. So, the lower esophageal sphincter plays a vital role in the digestive process by controlling the movement of food and protecting the esophagus from harmful acid.