The lower esophageal sphincter (LES) is a functional sphincter formed by the intrinsic circular smooth muscle of the distal esophagus augmented by the external sling of the right diaphragmatic crus encircling the esophageal hiatus. The angle of His (the acute angle between the cardia and the esophagus) contributes to LES competence. A hiatus hernia displaces the external diaphragmatic reinforcement, reducing total LES pressure.
| Origin | Circular smooth muscle of the distal 3-4 cm of esophagus, reinforced by the right crus of the diaphragm externally at the hiatus |
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| Insertion | Continuous with the circular muscle of the gastric cardia; no discrete tendinous insertion |
| Nerve Supply | Vagus nerve (CN X); myenteric (Auerbach) plexus intrinsic innervation; nitric oxide-mediated relaxation; acetylcholine-mediated contraction |
| Blood Supply | Left gastric artery; inferior phrenic artery branches |
| Actions | Maintains a high-pressure zone (10-45 mmHg above gastric pressure) at the gastroesophageal junction preventing gastric reflux into the esophagus; transiently relaxes to allow swallowed food to enter the stomach; also relaxes in transient lower esophageal sphincter relaxations (TLESRs) which are the primary mechanism of GORD |
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LES incompetence causes gastroesophageal reflux disease (GORD). Achalasia is the failure of LES relaxation from loss of inhibitory neurons, producing dysphagia and megaesophagus. Heller myotomy divides the LES circular muscle on the anterior esophagus and cardia. Fundoplication (Nissen 360 degrees, Toupet 270 degrees) augments LES pressure by wrapping gastric fundus around the distal esophagus, treating GORD and hiatus hernia.
Loss of the inhibitory myenteric plexus neurons at the LES produces failure of deglutitive LES relaxation and aperistalsis of the esophageal body, causing progressive dysphagia, regurgitation, and weight loss; Heller laparoscopic myotomy with partial fundoplication is the definitive surgical treatment.
