Swallowing (Deglutition)

Swallowing, or deglutition, is the coordinated sequence that moves a bolus from the mouth, through the pharynx, and into the esophagus while protecting the airway. It is conventionally described in phases: an oral preparatory and oral transport phase under voluntary control, followed by a rapid, largely reflexive pharyngeal phase, and then an esophageal phase that carries the bolus to the stomach. Its timing is orchestrated by brainstem circuits acting on more than two dozen muscles.

Definition

Swallowing (deglutition) is the coordinated neuromuscular sequence that transports a bolus from the oral cavity through the pharynx and esophagus to the stomach while temporarily protecting the airway.

Scope

This topic covers the physiology of normal swallowing: the phases of deglutition, the muscles and structures involved in each, the mechanisms of airway protection, and the brainstem central pattern generator and sensory feedback that organize the swallow. It does not cover the evaluation or treatment of swallowing disorders.

Core questions

• What are the phases of swallowing and what happens in each?
• How is the airway protected during the pharyngeal phase?
• How does the brainstem central pattern generator organize the swallow?
• How does sensory feedback trigger and shape the swallowing sequence?

Key concepts

• Oral preparatory and oral transport phases
• Pharyngeal phase and swallow triggering
• Esophageal phase
• Airway protection and laryngeal elevation
• Swallowing central pattern generator
• Upper esophageal sphincter relaxation and opening
• Sensory feedback from the oropharynx

Mechanisms

In the oral phases, the bolus is positioned and then propelled backward by the tongue against the palate toward the pharynx. Sensory stimulation of the oropharynx triggers the pharyngeal phase, a rapid and stereotyped sequence in which the soft palate seals the nasopharynx, the larynx elevates and closes and the epiglottis deflects to protect the airway, pharyngeal constrictors propel the bolus, and the upper esophageal sphincter relaxes and is pulled open to admit it. The esophageal phase then carries the bolus by peristalsis to the stomach. The whole sequence is organized by a central pattern generator in the brainstem (within the nucleus tractus solitarius and surrounding reticular formation), which receives sensory input and drives the cranial motor nuclei in the correct order, so that propulsion and airway protection are tightly synchronized.

Clinical relevance

Because swallowing both transports food and protects the airway, its normal physiology is the reference point for understanding oropharyngeal dysphagia and the risk of material entering the airway. This entry describes how normal swallowing works and how it is studied; it is educational reference material, not guidance for assessing or managing swallowing problems in any individual.

Evidence & guidelines

The description here is based on reviews of feeding and swallowing physiology and of swallowing neurophysiology, which integrate videofluoroscopic, manometric, and electromyographic studies of the normal swallow and experimental work on the brainstem swallowing network.

Seminal works

• jean-2001
• matsuo-palmer-2008
• ertekin-aydogdu-2003

Frequently asked questions

What are the phases of swallowing?

Swallowing is usually described as an oral preparatory and oral transport phase under voluntary control, a rapid reflexive pharyngeal phase that propels the bolus while protecting the airway, and an esophageal phase that carries the bolus to the stomach.

How is the airway protected during a swallow?

During the pharyngeal phase the larynx elevates and closes, the vocal folds adduct, and the epiglottis deflects over the laryngeal inlet, while breathing briefly pauses, so the bolus is directed into the esophagus rather than the airway.