Anatomy and physiology of the gastroesophageal junction.

The gastroesophageal junction is a complex valve composed of a smooth muscle element (LES) and a diaphragmatic element. These normally supplement each other to maintain competence in a static condition and during dynamic stresses associated with increased intra-abdominal pressure or swallowing. These sphincteric components also interact with each other pathophysiologically. During swallowing, large hernias impair the process of esophageal emptying, thereby prolonging acid clearance. The susceptibility to stress reflux inherent during periods of diminished LES pressure is also dramatically increased by disabling the diaphragmatic sphincter. These functional impairments of the gastroesophageal junction associated with hiatus hernia lead to increased esophageal acid exposure and offer one explanation for the chronicity of reflux disease.