The junction between the esophagus and the stomach is a specialized region,composed of lower esophageal sphincter (LES) and its adjacent anatomical structures,the gastric sling and crural diaphragm.Together these structures work in a coordinated manner to allow ingested food into the stomach while preventing reflux of gastric contents across the esophago-gastric junction (EGJ) into the esophagus.The same zone also permits retrograde passage of air and gastric contents into esophagus during belching and vomiting.The precise coordination required to execute such a complicated task is achieved by a finely-regulated high-pressure zone.This zone keeps the junction between esophagus and stomach continuously closed,but is still able to relax briefly via input from inhibitory neurons that are responsible for its innervation.Alterations of the structure and function of the EGJ and the LES may predispose to gastroesophageal reflux disease (GERD).