Lower esophageal sphincter (LES)

The **lower esophageal sphincter** is a specialized region of involuntary smooth muscle located at the junction between the esophagus and stomach. Its primary function is to act as a barrier that prevents gastric contents from refluxing into the esophagus. The LES remains closed except during swallowing, when it relaxes briefly to allow food and liquids to pass into the stomach. Dysfunction or weakness in this sphincter is associated with conditions such as gastroesophageal reflux disease (GERD), achalasia, and hiatal hernia[1][3][5]. The LES is sometimes referred to by alternative names including "gastroesophageal sphincter," "gastroesophageal junction," or "cardiac sphincter" due to its anatomical location near the heart[1][3]. It is classified anatomically rather than molecularly—unlike receptors or enzymes—and thus does not fit standard definitions for therapeutic drug targets like proteins or genes. **Note:** The lower esophageal sphincter is an anatomical structure composed of smooth muscle fibers rather than a discrete molecule/receptor/protein. It does not meet criteria for typical drug targets used in pharmacology databases; therefore, it should be flagged as an incorrect entry if searching for canonical molecular targets[1][3][8].

Other names

Gastroesophageal sphincterGastroesophageal junctionCardiac sphincter

Not applicable; drugs do not directly target the LES as a molecular entity but may influence its tone or the consequences of its dysfunction.