It begins at the base of the skull and ends inferiorly to the cricoid cartilage (C6). It is comprised of three parts; the nasopharynx, oropharynx and laryngopharynx (from superior to inferior).
In this article, we shall look at the anatomy of the pharynx – its structure, neurovascular supply, and any clinical correlations.
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.
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.
- Runs from the pterygoid hamulus, pterygomandibular raphe, the mandible and the side of the tongue to the pharyngeal tubercle of the occiput.
- Middle pharyngeal constrictor is found in the laryngopharynx.
- Originates from the stylohyoid ligament and the horns of the hyoid to the pharyngeal raphe.
- 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.
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.
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).
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.
Subdivisions of the Pharynx
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 posterosuperior 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 is the middle part of the pharynx, located between the soft palate and the superior border of the epiglottis. It contains the following structures:
- 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.
Clinical Relevance: Tonsillitis
The palatine tonsils can become 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.
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 tonsillar branch of the facial artery.
If an infection spreads to the peritonsillar tissue, it can cause abscess formation. This can cause deviation of the uvula, 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 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: Pharyngeal Diverticulum (Pouch)
It is relevant to recall that the inferior pharyngeal constrictor is split into two parts; the thyropharyngeus and the cricopharyngeus. This area between the two is a weak area in the mucosa.
Normally during swallowing, the thyropharyngeus contracts as the cricopharyngeus relaxes, allowing the bolus of food to be propelled into the oesophagus and preventing the intrapharyngeal pressure from 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.