Article: Swallowing

Swallowing, known scientifically as deglutition, is the reflex in the human body that makes something pass from the mouth, through the esophagus. If this fails and the object goes through the trachea, then choking occurs if the airway is completely blocked, or pulmonary aspiration occurs if the object is drawn into the lungs. The mechanism for swallowing is co-ordinated by the swallowing centre in the medulla oblongata and pons. The reflex is initiated by touch receptors in the pharynx as a bolus of food is pushed to the back of the mouth by the tongue.

Normal swallowing consists of three phases: oral, pharyngeal, and esophageal. Disorders of the oral or pharyngeal phases may lead to oropharyngeal dysphagia and disorders of the esophageal may lead to esophageal dysphagia.

Oral preparatory phase

In this phase, the food is processed by chewing (mastication) the bolus to an appropriate size to pass through the pharynx and esophagus. The tongue is an important player in this phase. When the bolus is ready to enter the next stage, it is first moved to the back of the tongue. Next, the anterior tongue lifts to the hard palate and retracts posterior to force the bolus to the upper pharynx. Then, the posterior tongue is lifted by the mylohyoid muscles, which also elevates the soft palate and seals the nasopharynx to prevent nasal aspiration. This phase is voluntary and involves important cranial nerves: V (trigeminal), VII (facial), and (XII) hypoglossal.

Pharyngeal phase

In this phase, the bolus is advanced from the pharynx to the esophageal through peristalsis. The soft palate is elevated to the posterior nasopharyngeal wall. The palatopharyngeal folds on each side of the pharynx are brought close together through the superior constrictor muscles, so that only boluses of an approximately small size can pass. Then the larynx and hyoid are elevated and pulled forward to the epiglottis to relax the cricopharyngeus muscle. This passively shuts off its entrance and the vocal cords are pulled close together, narrowing the passageway between them. This phase is passively controlled reflexively and involves cranial nerves V, X (vagus), XI (accessory), and XII.

• The respiratory centre of the medulla is directly inhibited by the swallowing centre for the very brief time that it takes to swallow. This is known as deglutition apnoea.

Esophageal phase

The upper oesophageal sphincter relaxes to let food past, after which various striated constrictor muscles of the pharynx as well as peristalsis and relaxation of the lower esophageal sphincter sequentially push the bolus of food through the esophagus into the stomach.

In terminally ill patients, a failure of the reflex to swallow leads to a buildup of mucous or saliva in the throat and airways, producing a noise known as a death rattle.

See also

• dysphagia