The Pharynx

Author: Nandhaa Pazhaniappan

Last modified: August 7, 2014

Fig 1.0 - The pharynx in relation to the nasal and oral cavities.

Fig 1.0 – The pharynx in relation to the nasal and oral cavities.

The pharynx is a muscular tube that connects the nasal cavities to the larynx and oesophagus. It is common to both the alimentary and the respiratory tract.

The tube begins at the base of the skull and ends inferior to the cricoid cartilage (C6). It is comprised of three parts; the nasopharynx, oropharynx and laryngopharynx (from superior to inferior).

When analysed cross-sectionally, it is comprised of pharyngeal mucosa, an incomplete ring of lymphoid tissue, a longitudinal muscle layer, a circular muscle layer and buccopharyngeal fascia (from medial to lateral).

In this article, we shall look at the structures of the pharynx, the neurovascular supply, and the three constituent parts of the pharynx.


Muscles

There are two types of muscles that form the walls of the pharynx – longitudinal and circular. Both types are innervated by the vagus nerve, except for the stylopharyngeus, which is innervated by the glossopharyngeal nerve.

Circular

Fig 1.1 -  Lateral view of the deep structures of the pharynx. Visible are the circular muscles of the pharynx, and the stylopharyngeus.

Fig 1.1 – Lateral view of the deep structures of the pharynx. Visible are the circular muscles of the pharynx, and the stylopharyngeus.

The circular muscles contract sequentially from superior to inferior to constrict the lumen and propel the bolus of food inferiorly into the oesophagus.

They are stacked like glasses and are an incomplete muscular circle, anteriorly attaching to structures in the neck.

They are all innervated by the vagus nerve (CN X)

  • Superior pharyngeal constrictor is found in the oropharynx
  • Middle pharyngeal constrictor is found in the laryngopharynx
  • Inferior pharyngeal constrictor is found in the laryngopharynx and has two components. The superior component (thyropharyngeus) has oblique fibres that attach to the thyroid cartilage and the inferior component (cricopharyngeus) has horizontal fibres that attach to the cricoid cartilage.

Longitudinal

The longitudinal muscles shorten and widen the pharynx, and elevate the larynx during swallowing.

  • Stylopharyngeus: from the styloid process of the temporal bone to the pharynx, innervated by the glossopharyngeal nerve (CN IX)
  • Palatopharyngeus: from hard palate of the oral cavity to the pharynx, innervated by the vagus nerve (CN X)
  • Salpingopharyngeus: from the Eustachian tube to the pharynx, innervated by the vagus nerve (CN X). In addition to contributing to swallowing, it also opens the Eustachian tube to equalize the pressure in the middle ear with the atmosphere.
Fig 1.2 - Posterior view of the pharynx. The pharynx has been split down the midline and opened, to show the longitundinal muscles.

Fig 1.2 – Posterior view of the pharynx. The pharynx has been split down the midline and opened, to show the longitundinal muscles.


Innervation

Innervation of the majority of the pharynx is achieved by the pharyngeal plexus, which comprises of:

  • Branches of the glossopharyngeal nerve (CN IX)
  • Branches of the vagus nerve (CN X)
  • Sympathetic fibres of the superior cervical ganglion.

Sensory: Each of the three sections of the pharynx have a different innervation:

  • The nasopharynx is innervated by the maxillary nerve (CN V2).
  • The oropharynx by the glossopharyngeal nerve (CN IX).
  • The laryngopharynx by the vagus nerve (CN X).

Motor: All the muscles of the pharynx are innervated by the vagus nerve (CN X), except for the stylopharyngeus, which is innervated by the glossopharyngeal nerve (CN IX).


Blood Supply

Arterial supply is via branches of the external carotid artery: ascending pharyngeal, lingual, facial and maxillary arteries.

Venous drainage is achieved by the pharyngeal venous plexus, which drains into the internal jugular vein.

Fig 1.3 - Vasculature of the pharynx. Right arterial supply via the ECA and left venous plexus shown.

Fig 1.3 – Vasculature of the pharynx. Right arterial supply via the ECA and left venous plexus shown.


Divisions of the Pharynx

The Nasopharynx

Fig 1.5 - The three parts of the pharynx, and their borders.

Fig 1.5 – The three parts of the pharynx, and their borders.

The nasopharynx is found between the base of the skull and the soft palate, it is a continuation of the nasal cavity. It performs a respiratory function by conditioning inspired air and propagating it to the larynx.

This part of the pharynx is lined with respiratory epithelium: ciliated pseudo-stratified columnar epithelium with goblet cells.

The posterio-superior nasopharynx contains the adenoid tonsils, which are large between the ages of 3-8 and then regress.

Clinical Relevance: Enlarged Adenoid Tonsils

The adenoid tonsils can become pathologically enlarged due to viral infections of the upper respiratory tract. In the case of recurrent infections, they can become chronically enlarged. When enlarged, the adenoids can obstruct the opening of the eustachian tube which is located close to the adenoid tonsils in the nasopharynx.

Chronic obstruction of the eustachian tube prevents the equalizing of pressure in the middle ear with the atmosphere and normal drainage of fluids for excretion. This can lead to chronic otitis media with effusion, colloquially known as glue ear. In this condition, the static fluid and negative pressure in the middle ear provides the ideal environment for infection.


The Oropharynx

The oropharynx is the middle part of the pharynx, located between the soft palate and the superior border of the epiglottis.

It contains:

  • Posterior 1/3 of the tongue.
  • The lingual tonsils – Located inferiorly to the tongue.
  • The palatine tonsils – Found in the tonsillar fossa between the palatoglossal and palatopharyngeal arches of the oral cavity.
  • Superior constrictor muscle

The oropharynx is involved in the voluntary and involuntary phases of swallowing.

Fig 1.4 - Location of the palatine tonsil in the oropharynx

Fig 1.4 – Location of the palatine tonsil in the oropharynx

Clinical Relevance: Inflammed Palatine Tonsils (Tonsillitis)

The palatine tonsils can becomes inflamed due to a viral or bacterial infection. In such a case, they appear red and enlarged, and are accompanied by enlarged jugulo-digastric lymph nodes.

Fig 1.4 - Quinsy - inflammation of the peritonsillar tissue. Note also how the uvula has deviated to the right as a result of the inflammation.

Fig 1.4 – Quinsy – inflammation of the peritonsillar tissue. Note also how the uvula has deviated to the right as a result of the inflammation.

Chronic infection of the palatine tonsils can be treated with their removal, a tonsillectomy. When performing a tonsillectomy, there may be bleeding primarily from the external palatine vein and secondarily from the tonsilar branch of the facial artery.

Additionally, the glossopharyngeal nerve (CN IX) and internal carotid artery are located lateral to the tonsilar fossa and may be damaged during a tonsillectomy.

If an infection spreads to the peritonsillar tissue, it can cause abscess formation. This can cause deviation of the uvula this is known as quinsy. A quinsy is a medical emergency, as it can potentially cause obstruction of the pharynx. It is treated with draining of the abscess and antibiotics.


The Laryngopharynx

The most distal part of the pharynx, this is located between the superior border of the epiglottis and inferior border of the cricoid cartilage (C6), at which point it becomes continuous with the oesophagus. It is found posterior to the larynx and communicates with it via the laryngeal inlet, lateral to which one can find the piriform fossae.

The laryngopharynx contains the middle and inferior pharyngeal constrictors.

Clinical Relevance: Foreign Objects

Foreign objects can become lodged in two sites in the pharynx:

  1. The valleculae in the nasopharynx
  2. The piriform fossae in the laryngopharynx.

The objects found in latter site are visualized and removed by a pharyngoscope. Objects lodged in the piriform fossae can compress the internal laryngeal nerve and recurrent laryngeal nerve.

Clinical Relevance: Pharyngeal Diverticulum (Pouch)

It is relevant to recall that the inferior pharyngeal constrictor is split into two parts; the thyropharyngeus and the cricopharyngeus. The area between the two an weak area in the muscosa.

Normally during swallowing, the thryopharyngeus contracts as the cricopharyngeus relaxes, allowing the bolus of food to be propelled into the oesophagus and preventing the intrapharyngeal pressure form rising. If this coordinated relaxation of the cricopharyngeus does not occur, the intrapharyngeal pressure tends to rise and pharyngeal mucosa forms a midline diverticulum in the area between the thyropharyngeus and cricopharyngeus. It is possible for food to accumulate here, leading to dysphagia.

Fig 1.5 - Pharyngeal diverticulum.

Fig 1.5 – Pharyngeal diverticulum.