Pharynx and Tonsillar Region

A muscular tube extending from the skull base to the level of the cricoid cartilage (C6), where it becomes continuous with the oesophagus, shared between the respiratory and digestive systems, subdivided into three parts.

Nasopharynx:

• Extends from the skull base to the soft palate, posterior to the nasal cavity (communicating via the choanae), containing the pharyngeal tonsil (adenoid) on its posterosuperior wall and the tubal tonsils/pharyngeal recess (fossa of Rosenmüller) flanking the auditory tube openings, purely respiratory in function, lined by respiratory (ciliated pseudostratified columnar) epithelium.

Oropharynx:

• Extends from the soft palate to the upper border of the epiglottis, posterior to the oral cavity (communicating via the oropharyngeal isthmus), containing the palatine tonsils within the tonsillar fossae (between the palatoglossal and palatopharyngeal folds) and the lingual tonsil on the tongue's posterior third, shared respiratory/digestive function, lined by stratified squamous epithelium (reflecting its exposure to abrasive food passage).

Laryngopharynx (hypopharynx):

• Extends from the upper border of the epiglottis to the lower border of the cricoid cartilage (continuing as the oesophagus), lying posterior to the larynx, containing the piriform recesses (paired mucosal recesses flanking the laryngeal inlet, a common site for lodged foreign bodies/fish bones, and closely related to the internal laryngeal nerve), shared function, stratified squamous epithelium.

• The pharyngeal wall is formed by an outer circular layer of constrictor muscles and an inner longitudinal layer of elevator muscles, working together to propel a food bolus downward during swallowing while elevating/shortening the pharynx.

Superior constrictor:

• Origin: Pterygoid hamulus, pterygomandibular raphe, mylohyoid line of the mandible.
• Insertion: Pharyngeal raphe (posterior midline), pharyngeal tubercle of the occipital bone.
• Innervation: Vagus nerve (CN X), via pharyngeal plexus.
• Action: Constricts the upper pharynx during swallowing.

Middle constrictor:

• Origin: Stylohyoid ligament, lesser and greater horns of the hyoid bone.
• Insertion: Pharyngeal raphe.
• Innervation: Vagus nerve (CN X), via pharyngeal plexus.
• Action: Constricts the middle pharynx.

Inferior constrictor:

• Origin: Oblique line of the thyroid cartilage and the cricoid cartilage (two parts, thyropharyngeus and cricopharyngeus, the latter functioning as the upper oesophageal sphincter, normally tonically contracted at rest to prevent air entry into the oesophagus during breathing and reflux from below).
• Insertion: Pharyngeal raphe.
• Innervation: Vagus nerve (CN X), via pharyngeal plexus.
• Action: Constricts the lower pharynx; the cricopharyngeus part relaxes momentarily during swallowing to allow bolus passage into the oesophagus.

Longitudinal muscles (elevators):

• Stylopharyngeus: Origin, styloid process of the temporal bone; Action, elevates the pharynx/larynx during swallowing; Innervation: glossopharyngeal nerve (CN IX), the sole pharyngeal muscle with this innervation, and CN IX's only motor function overall.
• Salpingopharyngeus: Origin, cartilaginous part of the auditory tube; Action, elevates the pharynx, opens the auditory tube during swallowing; Innervation, vagus nerve (CN X), via pharyngeal plexus.
• Palatopharyngeus: Origin, palatine aponeurosis (soft palate); Action, elevates the pharynx/larynx, narrows the oropharyngeal isthmus; Innervation, vagus nerve (CN X), via pharyngeal plexus.

• Small gaps between the constrictor muscles (where each constrictor overlaps the one below it, "telescoping" downward) permit the passage of structures entering/leaving the pharyngeal wall.

• Above superior constrictor (between it and the skull base): Auditory tube, ascending palatine artery, levator veli palatini.
• Between superior and middle constrictors: Stylopharyngeus, glossopharyngeal nerve (CN IX), stylohyoid ligament.
• Between middle and inferior constrictors: Internal laryngeal nerve, superior laryngeal artery/vein.
• Below inferior constrictor (between it and the oesophagus, at Killian's dehiscence: see Applied Anatomy): Recurrent laryngeal nerve, inferior laryngeal artery.

Pharyngeal plexus:

• Formed predominantly on the middle constrictor's outer surface by contributions from the vagus nerve (motor to all pharyngeal muscles except stylopharyngeus, and sensory to most of the pharynx) and the glossopharyngeal nerve (sensory, predominantly to the oropharynx, plus its unique motor contribution to stylopharyngeus), with additional sympathetic contributions from the superior cervical ganglion.
• Represents the shared final common motor pathway for essentially all pharyngeal muscle activity, explaining why vagal (or, less commonly, combined vagal/glossopharyngeal) lesions cause the characteristic pharyngeal/swallowing dysfunction (palatal deviation, absent gag reflex).

Glossopharyngeal nerve (CN IX):

• Provides the sole motor supply to stylopharyngeus and the dominant sensory supply to the oropharynx (including the palatine tonsils), plus its contribution to the pharyngeal plexus and the gag reflex's afferent limb.

• Multiple arterial contributions from the external carotid artery's branches converge on the pharyngeal wall: the ascending pharyngeal artery (direct branch, the most consistent single contributor), branches of the facial artery (ascending palatine, tonsillar branches), the lingual artery (to the tongue base/lower oropharynx), and the maxillary artery (via the greater palatine and pharyngeal branches, to the nasopharynx/upper pharynx), reflecting the extensive external carotid arterial territory covered in Section 5.

Palatine tonsil:

• Located within the tonsillar fossa, between the anterior (palatoglossal) and posterior (palatopharyngeal) pillars/folds/arches, in the lateral oropharyngeal wall, the largest and most clinically significant component of Waldeyer's ring.

Tonsillar bed:

• The tonsil sits against a fibrous capsule, external to which lies loose areolar tissue, then the superior constrictor muscle: this capsule/loose tissue plane is the surgical plane of dissection used in tonsillectomy.

Blood supply:

• Multiple contributors converge here too, though the dominant supply is the tonsillar branch of the facial artery, piercing the superior constrictor to reach the tonsil's lower pole, with additional contributions from the ascending pharyngeal artery, ascending palatine artery (facial artery branch), lingual artery (dorsal lingual branches), and the descending palatine artery (via its lesser palatine branch, maxillary artery), this rich, multi-source supply is directly relevant to the risk of significant post-tonsillectomy haemorrhage (see Applied Anatomy).

Venous drainage:

• Via the paratonsillar vein, which descends alongside the tonsil's capsule (closely related to the tonsil, notable as a structure that must be carefully identified/avoided or controlled during tonsillectomy) to join the pharyngeal venous plexus/facial vein.

Innervation:

• Sensory supply from both the glossopharyngeal nerve (CN IX, the dominant contributor, explaining why tonsillitis commonly causes referred otalgia via CN IX's shared innervation of the middle ear region) and the lesser palatine nerve (branch of the maxillary division, CN V2, via the pterygopalatine ganglion pathway), this dual sensory innervation from two different cranial nerves is the anatomical basis for the ear pain commonly associated with tonsillitis/pharyngitis.

• A ring of lymphoid tissue encircling the entrance to the pharynx (nasopharynx/oropharynx junction region), providing immune surveillance for inhaled/ingested antigens at this critical entry point, composed of four named components:

• Pharyngeal tonsil (adenoid): Nasopharynx, posterosuperior wall, a single, midline structure (unlike the paired palatine tonsils).
• Tubal tonsils: Paired, surrounding the auditory tube openings in the lateral nasopharyngeal wall.
• Palatine tonsils: Paired, within the oropharyngeal tonsillar fossae (the largest, most clinically prominent component).
• Lingual tonsil: Single, on the posterior one-third (pharyngeal part) of the tongue's dorsal surface.

• Together these four components form an anatomically continuous (or near-continuous) ring of lymphoid tissue at the pharyngeal inlet, a unifying immunological/anatomical concept worth visualising as a genuine "ring" even though the individual named tonsils are anatomically discrete structures in different specific locations.

Tonsillectomy bleeding:

• Given the tonsil's rich, multi-source arterial supply, post-tonsillectomy haemorrhage is a well-recognised complication, occurring either in the immediate postoperative period (primary haemorrhage, from inadequate intraoperative haemostasis) or, notably, 5-10 days postoperatively (secondary haemorrhage, related to sloughing of the healing tonsillar bed's fibrinous coating as infection/inflammation resolves), both scenarios requiring prompt recognition given the airway proximity and potential for significant blood loss.

Glossopharyngeal nerve relationship:

• The close anatomical relationship between the tonsillar bed and the glossopharyngeal nerve's course (running just deep/lateral to the tonsillar fossa, within the loose areolar tissue plane before it passes between the superior and middle constrictors, see Pharyngeal Gaps above) creates a risk of iatrogenic CN IX injury during tonsillectomy if dissection extends too deeply/laterally beyond the correct capsular plane.

Peritonsillar abscess (quinsy):

• A collection of pus in the peritonsillar space (between the tonsillar capsule and the superior constrictor muscle), typically arising as a complication of acute tonsillitis, presenting with severe unilateral throat pain, trismus (from adjacent muscle irritation/spasm, given the pterygoid muscles' proximity), and a characteristic "hot potato" muffled voice, with visible displacement of the affected tonsil and uvula toward the contralateral side, managed by needle aspiration or incision and drainage, guided by the same tonsillar bed anatomy relevant to tonsillectomy.

Pharyngeal foreign bodies:

• Commonly lodge in the piriform recess (laryngopharynx) or, less commonly, within the tonsillar crypts/lingual tonsil region, the piriform recess's close relationship to the internal laryngeal nerve (running just beneath its mucosa) means a lodged sharp foreign body (e.g., a fish bone) here can cause localised sensory disturbance or, if it perforates deeply, risk injury to this nerve or the adjacent great vessels of the neck.