Control of swallowing deglutition

Swallowing can be divided into three phases:

• pharyngeal

• oesophageal

Voluntary phase

The tongue moves food backwards and upwards into the back of the mouth. This is initiated voluntarily but once it has been initiated it cannot be stopped voluntarily, it is a classical 'all or none' reflex.

Pharyngeal phase

As the food moves into the pharynx, it activates pressure receptors in the pharynx. These receptors send impulses via the trigeminal and glossopharyn-

geal nerves to the brain stem swallowing centre. Each impulse serves as a trigger for the swallowing reflex. This causes the elevation of the soft palate, which seals the nasal cavity and prevents food entering it. The swallowing centre inhibits respiration by raising the larynx and closing the glottis to prevent food entering the trachea. The upper oesophageal sphincter, which is closed at rest, opens during swallowing to allow the bolus of food to pass into the oesophagus. Immediately after the bolus has passed, the sphincter closes again, resealing the junction. The pharyngeal phase of swallowing lasts approximately one second (Figure 3.1).

Oesophageal phase

As the peristaltic waves commence in the oesophagus, the muscle of the lower oesophageal sphincter relaxes, opening the sphincter and allowing the food bolus to enter the stomach. The lower oesophageal sphincter muscle then contracts to reseal the junction. The lower oesophageal sphincter remains closed in the absence of peristalsis, preventing the reflux of the acidic contents of the stomach into the oesophagus (Figure 3.2).

Figure 3.1 Pharyngeal phase of swallowing. Reproduced by permission of Hodder Arnold from Clancy and McVicar (2002).
Figure 3.2 Oesophageal phase of swallowing. Reproduced by permission of Hodder Arnold from Clancy and McVicar (2002).
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