Physiology, Lower Esophageal Sphincter

The esophagus is a portion of the digestive system connecting the pharynx to the stomach, allowing the passage of food for digestion (see Digestive and Respiratory Anatomical Structures Connected to the Esophagus). The esophagus measures approximately 25 cm long in a mature adult and begins at the inferior border of the cricoid cartilage (C6 level), descending in the posterior mediastinum through the esophageal hiatus of the diaphragm and terminating at the stomach (T11 level). During its course, the esophagus encounters 3 anatomic constrictions: at the level of the cricopharyngeus muscle, as it travels posterior to the aortic arch/left mainstem bronchus, and at the level of the esophageal hiatus of the diaphragm. These areas of constriction are considered the most frequent sites for a foreign body or food impaction to occur. The esophagus has 2 functional sphincters, the upper and lower esophageal sphincters. The upper esophageal sphincter (UES) is a high-pressure zone at the transition of the pharynx and the cervical esophagus. The lower esophageal sphincter (LES) is a high-pressure zone located where the esophagus meets the stomach and protects the esophagus from the reflux of gastric contents. The LES is composed of intrinsic and extrinsic components. The intrinsic component of the LES consists of esophageal muscle fibers and is under neurohormonal control. The extrinsic component consists of the diaphragmatic crura and the phrenoesophageal ligament, which provide anatomical support to the LES and further protection against gastric reflux.