Swallowing or deglutition is a complex process. It is usually initiated by the food bolus, formed and lubricated with saliva in the mouth, being actively pushed by the tongue towards the back of the throat or pharynx.¹²

This ‘voluntary’ muscle action then stimulates receptors in the pharynx to trigger the ‘involuntary’ muscle contraction of head and neck muscles. At the same time, other muscles move the palate and larynx to close the airway to the passing bolus.

The upper oesophageal sphincter opens almost immediately, and then shuts as soon as the bolus passes through. As the bolus enters the oesophagus, peristalsis is stimulated with the sequential contraction of circular muscle and then the opening of the lower oesophageal sphincter (LOS) at the junction between the oesophagus and stomach.