Lower esophageal sphincter muscle tissue (LES)

The lower esophageal sphincter muscle tissue (LES) is a ring of circular smooth muscle at the distal esophagus, directly above the stomach, serving as the main barrier preventing gastric contents from refluxing into the esophagus[1][3][4][5][6]. It maintains tonic contraction and is regulated by both myogenic and neural mechanisms, including autonomic and enteric nervous system inputs[2][3][6]. The LES relaxes transiently during swallowing or to allow gas venting (transient LES relaxation), and abnormal relaxation or incomplete closure leads to clinical disorders including gastroesophageal reflux disease and achalasia[2][4][6]. The muscle fibers of the LES are organized into clasp fibers and sling fibers, with differences in tone, innervation, and pharmacological responsiveness[2][3]. Pharmacologic manipulation and tissue motility assays often target these physiological mechanisms rather than the muscle tissue as a molecular entity[6]. Anatomically, the LES works in concert with the crural diaphragm, which augments the antireflux barrier at the esophagogastric junction[1][4][6].

Other names

Lower esophageal sphincterLESGastroesophageal sphincterCardiac sphincterEsophagogastric junction (EGJ; descriptive anatomical region)

Mechanism of action includes inhibition of smooth muscle contraction (e.g., via calcium channel blockade or nitrate-induced relaxation), cholinergic stimulation to increase tone, inhibitory neuromodulation (e.g., botulinum toxin prevents acetylcholine release), and enhancement of myogenic tone (e.g., by prokinetic drugs).