Deglutition (swallowing)
Deglutitio
Also known as: swallowing, swallow reflex
Deglutition moves a bolus from the mouth to the stomach. It has a voluntary oral phase followed by reflex pharyngeal and oesophageal phases, coordinated by a swallowing centre in the medulla.
Overview
Swallowing is run by a central pattern generator in the medulla. Sensory input arrives at the nucleus tractus solitarius, and motor output leaves from the nucleus ambiguus (pharyngeal and upper oesophageal striated muscle) and the dorsal motor nucleus of the vagus (smooth muscle). The same circuit briefly inhibits breathing (deglutition apnoea). Adults swallow several hundred times a day, many of those swallows being saliva.
The oral phase is voluntary. The tongue (XII) presses the bolus up against the hard palate and sweeps it back into the oropharynx.
The pharyngeal phase is involuntary and lasts about 1 second. It begins when the bolus touches receptors around the faucial pillars and posterior pharynx (afferents in IX and X). In rapid sequence the soft palate rises to seal the nasopharynx, and the palatopharyngeal folds approximate so that only a moderate-sized bolus can pass. The vocal folds adduct and the larynx and hyoid are pulled up and forward by the suprahyoid and thyrohyoid muscles, tucking the larynx under the tongue base while the epiglottis tilts back over the laryngeal inlet. The upper oesophageal sphincter relaxes and is pulled open by the rising larynx. Finally the pharyngeal constrictors contract from above downwards and drive the bolus into the oesophagus.
The oesophageal phase is also involuntary. Primary peristalsis continues the pharyngeal wave and travels at about 2–4 cm/s, reaching the stomach in about 8–10 s. Any bolus left behind distends the wall and triggers secondary peristalsis, which is mediated locally by the enteric nervous system. The LES and the proximal stomach relax ahead of the wave (receptive relaxation, a vagovagal reflex). When upright, liquids reach the stomach faster, helped by gravity.
Parts & subdivisions
- Tongue-driven transfer of the bolus to the oropharynx. Impaired in cranial nerve palsies and after stroke.
- Velopharyngeal closure, airway protection (vocal fold adduction, laryngeal elevation, epiglottic tilt), UES opening and constrictor contraction.
- Primary and secondary peristalsis, then LES relaxation.
- Vocal fold closure is the most important protective step. The epiglottis acts as a deflector.
Anatomy
- Innervation
Afferent: V, IX and X (superior laryngeal nerve). Efferent: V (mylohyoid, anterior digastric, tensor veli palatini), VII (posterior digastric, stylohyoid), IX (stylopharyngeus), X (palate, pharyngeal constrictors, larynx, oesophagus), XII (tongue) and C1–C3 (infrahyoid muscles).
Function
- Moves the bolus safely from the mouth to the stomach while protecting the airway.
- Clears saliva and refluxed material from the pharynx and oesophagus.
- Opens the auditory tubes (via tensor veli palatini).
- Physiology
Integrated in the medullary swallowing centre, which inhibits respiration during the pharyngeal phase. Oesophageal peristalsis depends on vagal sequencing in the striated upper oesophagus. In the smooth lower oesophagus it can be generated by the myenteric plexus alone.
Clinical significance
Dysphagia
Oropharyngeal dysphagia is difficulty starting a swallow, with coughing and nasal regurgitation. It is seen in stroke, motor neurone disease, myasthenia gravis and Parkinson disease, and carries a risk of aspiration pneumonia, usually in the right lower lobe. Oesophageal dysphagia is the sensation of food sticking. It may be mechanical (stricture, cancer, rings) or due to a motility disorder (achalasia, diffuse spasm, systemic sclerosis).
Pharyngeal pouch (Zenker diverticulum)
The mucosa herniates posteriorly through Killian dehiscence, a weak area between the thyropharyngeal and cricopharyngeal parts of the inferior constrictor. It causes regurgitation of undigested food, halitosis, gurgling and aspiration.
Compiled from standard anatomy and physiology references — see the Digestive System sources. For education only; not medical advice.