Learning Objective
By the end of this article, the learner should be able to describe the anatomy of the pharynx, including its subdivisions, muscular structure, innervation, vascular supply, and key clinical correlations.
Overview of the Pharynx
The pharynx is a fibromuscular tube that forms a shared passageway for the respiratory and digestive systems. It connects the nasal and oral cavities superiorly to the larynx and oesophagus inferiorly.
The pharynx extends from the base of the skull to the inferior border of the cricoid cartilage at vertebral level C6, where it becomes continuous with the oesophagus.
Anatomically, the pharynx is divided into three regions arranged from superior to inferior:
- Nasopharynx
- Oropharynx
- Laryngopharynx
Each subdivision has distinct anatomical boundaries, epithelial lining, functions, and clinical relevance.
In this article, we will explore the structure of the pharynx, its muscular organisation, neurovascular supply, and important clinical correlations relevant to swallowing, respiration, and pathology.
Nasopharynx
The nasopharynx lies between the base of the skull and the soft palate. It is continuous anteriorly with the nasal cavity and serves a primarily respiratory function, conditioning inspired air before it passes into the lower respiratory tract.
It is lined by respiratory epithelium (ciliated pseudostratified columnar epithelium with goblet cells).
The posterosuperior wall of the nasopharynx contains the adenoid tonsils, which are the largest between 3–8 years of age and typically regress after childhood.
Clinical Relevance – Enlarged Adenoid Tonsils
Recurrent upper respiratory tract infections may cause pathological enlargement of the adenoid tonsils. Enlarged adenoids can obstruct the nearby opening of the Eustachian tube, impairing middle ear ventilation and fluid drainage. This predisposes to otitis media with effusion (glue ear), characterised by persistent middle ear fluid and conductive hearing loss.
Oropharynx
The oropharynx extends from the soft palate superiorly to the superior border of the epiglottis inferiorly. It functions in both respiration and swallowing.
Key structures within the oropharynx include:
- Posterior one-third of the tongue
- Lingual tonsils at the base of the tongue
- Palatine tonsils, located in the tonsillar fossa between the palatoglossal and palatopharyngeal arches
- Superior pharyngeal constrictor muscle
Together with the adenoids and lingual tonsils, the palatine tonsils form Waldeyer’s ring, a ring of lymphoid tissue that provides immune defence at the entrance to the aerodigestive tract.
The oropharynx participates in both the voluntary and involuntary phases of swallowing.
Laryngopharynx
The laryngopharynx is the most inferior part of the pharynx. It extends from the superior border of the epiglottis to the inferior border of the cricoid cartilage (C6), where it continues as the oesophagus.
Located posterior to the larynx, it communicates with it through the laryngeal inlet. On either side of the inlet are the piriform fossae, which are clinically important sites where foreign bodies may lodge.
The laryngopharynx contains the middle and inferior pharyngeal constrictor muscles.
Clinical Relevance – Pharyngeal Diverticulum (Zenker’s Diverticulum)
The inferior pharyngeal constrictor consists of thyropharyngeal and cricopharyngeal parts, with a weak area between them. Failure of coordinated relaxation during swallowing can lead to increased intrapharyngeal pressure and formation of a pharyngeal diverticulum, resulting in dysphagia, regurgitation, and aspiration.
Muscles of the Pharynx
The pharyngeal muscles are arranged into two functional groups:
Circular (Constrictor) Muscles
- Superior
- Middle
- Inferior
These muscles contract sequentially from superior to inferior to propel the bolus of food into the oesophagus.
Longitudinal Muscles
- Stylopharyngeus
- Palatopharyngeus
- Salpingopharyngeus
They act to shorten and widen the pharynx and elevate the larynx during swallowing.
Innervation
Most motor and sensory innervation of the pharynx is via the pharyngeal plexus, formed by contributions from cranial nerves IX and X, along with sympathetic fibres.
- Motor: All pharyngeal muscles are innervated by the vagus nerve, except the stylopharyngeus (glossopharyngeal nerve).
- Sensory: Predominantly supplied by the glossopharyngeal nerve, with regional contributions from the trigeminal and vagus branches.
Vasculature
- Arterial supply: Branches of the external carotid artery, including the ascending pharyngeal, facial, lingual, and maxillary arteries.
- Venous drainage: Pharyngeal venous plexus drains into the internal jugular vein.
