Which structure prevents backflow of gastric contents into the esophagus?

The lower esophageal sphincter is a crucial muscular structure located at the junction of the esophagus and the stomach. Its primary function is to maintain a barrier that prevents the backflow of gastric contents into the esophagus. This sphincter remains closed, except during swallowing when it relaxes to allow food to enter the stomach. If this sphincter becomes weak or malfunctions, it can lead to gastroesophageal reflux disease (GERD), where stomach acids flow back into the esophagus, causing discomfort and potential damage to the esophageal lining. This mechanism is vital for protecting the esophagus from harsh stomach acids and maintaining proper digestive function.