Lower Oesophageal Sphincter Mechanisms

Expansion

• Right crus sling - muscular fibres pinch the oesophagus during inspiration and straining
• Angle of His - the acute angle between oesophagus and gastric fundus acts as a flap valve
• Intra-abdominal segment - compressed by positive abdominal pressure
• Mucosal rosette - redundant folds at the junction plug the lumen
• Phreno-oesophageal ligament - anchors the junction to the hiatus
• Tonic smooth muscle of the lower oesophagus

Note the absence of any thickened anatomical sphincter. Continence is the sum of these factors, which explains why a sliding hiatus hernia, which pulls the junction into the chest, straightens the angle of His and removes the abdominal segment, so reliably produces reflux.

Surgical fundoplication works by restoring the angle and recreating an intra-abdominal segment.