Describe the anatomy and physiology of the pharynx.

Divisions and Structure

• The pharynx is a musculomembranous tube extending from the skull base to the lower border of the cricoid cartilage (the level of C6), where it becomes the oesophagus.
• It is 12 to 14 cm long and is divided into nasopharynx, oropharynx and hypopharynx.
• The nasopharynx extends from the skull base to the level of the soft palate; it is a respiratory passage, lined largely by ciliated columnar epithelium, and contains the adenoid, the eustachian tube openings and the fossa of rosenmuller
• The oropharynx extends from the soft palate to the level of the hyoid (the tip of the epiglottis); it is a shared food and air passage, lined by stratified squamous epithelium, and contains the palatine tonsils, the base of tongue with the lingual tonsil, the soft palate and the posterior pharyngeal wall
• The hypopharynx (laryngopharynx) extends from the hyoid to the lower border of the cricoid, and has three subsites — the pyriform fossae, the postcricoid region and the posterior pharyngeal wall
• The wall has four layers — mucosa, a fibrous pharyngobasilar fascia, a muscular layer, and the buccopharyngeal fascia
• The muscles are the three constrictors (superior, middle and inferior).
• The longitudinal muscles are the stylopharyngeus, salpingopharyngeus and palatopharyngeus.
• The inferior constrictor has two parts.
• Cricopharyngeus is the upper oesophageal sphincter — tonically contracted at rest and relaxing during swallowing
• Killian’S dehiscence is the potential gap between thyropharyngeus and cricopharyngeus on the posterior wall — an area of relative weakness through which a pharyngeal pouch herniates. It is the "gateway of tears" for the endoscopist, being the commonest site of perforation during rigid oesophagoscopy
• Nerve supply — the pharyngeal plexus, formed by the glossopharyngeal (IX), vagus (X) and sympathetic contributions
• Motor supply is from the vagus (through the cranial accessory) to all muscles except stylopharyngeus.
• Sensory supply — the nasopharynx by the maxillary nerve (V2); the oropharynx by the glossopharyngeal; and the hypopharynx by the vagus (internal laryngeal branch)
• The gag reflex has a glossopharyngeal afferent and a vagal efferent
• Blood supply is from branches of the external carotid — the ascending pharyngeal, ascending palatine and tonsillar branches of the facial, the greater palatine, and the dorsal lingual arteries

Waldeyer Ring, Swallowing and Applied Anatomy

• Waldeyer’S ring is the ring of subepithelial lymphoid tissue guarding the entrance to the aerodigestive tract, comprising the adenoid (nasopharyngeal tonsil) above, the tubal tonsils, the palatine tonsils laterally, the lingual tonsil below, and lateral pharyngeal bands
• It is part of mucosa-associated lymphoid tissue (malt), sampling inhaled and ingested antigen and producing secretory IgA; it is most active between 4 and 10 years and involutes thereafter
• The palatine tonsil is worth describing in detail, since it is the commonest object of surgery in the chapter
• It lies in the tonsillar fossa, bounded by the palatoglossal arch anteriorly, the palatopharyngeal arch posteriorly, and the superior constrictor laterally
• It has a capsule of condensed pharyngobasilar fascia, and a loose peritonsillar space between capsule and superior constrictor — which is the plane of surgical dissection and the space in which a quinsy forms
• It has 12 to 15 crypts.
• Its blood supply is chiefly from the tonsillar branch of the facial artery, entering at the lower pole, with the ascending pharyngeal, ascending palatine, dorsal lingual and greater palatine arteries. The lower pole is the site of the main bleeding at tonsillectomy
• Venous drainage is to the paratonsillar vein, a further source of bleeding
• Nerve supply is by the glossopharyngeal nerve and the lesser palatine branches — which explains referred otalgia after tonsillectomy and in tonsillar disease, through the tympanic branch of IX (jacobson’S nerve)
• Lymphatic drainage is to the jugulodigastric (tonsillar) node, at the angle of the mandible