The passage of food from the esophagus to the stomach is primarily controlled by a muscular ring known as the lower esophageal sphincter (LES). This sphincter is located at the junction where the esophagus meets the stomach.
The LES acts like a valve; it opens to allow food and liquids to enter the stomach while preventing stomach contents, including acid, from flowing back into the esophagus. This mechanism is essential for proper digestion and helps to protect the esophagus from the corrosive effects of gastric acid.
When you swallow, the LES relaxes briefly to let food pass through. After the food has entered the stomach, the sphincter closes again, maintaining pressure in the stomach and aiding in digestion. If the LES is weak or relaxes inappropriately, it can lead to conditions such as gastroesophageal reflux disease (GERD), where acid flows back into the esophagus, causing discomfort and potential damage.