Regurgitation describes the passive movement of gastric contents into the pharynx. This is normally prevented by the upper and lower oesophageal sphincters.

The lower oesophageal sphincter is formed by the lowest 2-4 cm of the oesophagus. The major component of the upper oesophageal sphincter is the cricopharyngeus muscle.

If regurgitation occurs and gastric contents then enter the trachea and lungs, aspiration is said to have occurred.