Pharynx

Development

Formation of the pharyngeal (branchial) apparatus is during the 4th and 5th weeks of development.

The pharyngeal apparatus consists of:

• Arches
• Pouches
• Clefts
• Membranes that contribute to the development of the head and neck

Pharyngeal musculature develops from the 3rd, 4th, and 6th arches:

• The 3rd pharyngeal arch gives rise to the stylopharyngeus muscle.
• The remaining muscles (constrictor and longitudinal groups) emerge from the 4th and 6th arches.
• Of note, the 5th pharyngeal arch involutes early in development and does not contribute to fetal development.

Gross Anatomy

Characteristics

• 5 inches (12 cm) long
• Extends from the cranial base to the inferior border of the cricoid cartilage anteriorly and to the inferior border of the C6 vertebra posteriorly
• The pharynx is widest (approximately 5 cm) opposite the hyoid and narrowest (approximately 1.5 cm) at its inferior end, where it is continuous with the esophagus.

Divisions

• Nasopharynx:
  • From the base of the skull to the upper surface of the soft palate
  • Contains adenoids in the posterior wall
  • Has a respiratory function as it is the posterior extension of the nasal cavities
  • The nose opens into the nasopharynx through 2 choanae.
• Oropharynx:
  • Has a digestive function
  • Extends from the soft palate to the superior border of the epiglottis
  • Contains the palatine tonsils in the lateral walls
  • Boundaries:
    • Soft palate superiorly
    • Base of the tongue inferiorly
    • Palatoglossal and palatopharyngeal arches laterally
• Laryngopharynx:
  • Caudal region of the pharynx
    • Starts: superior border of the epiglottis
    • Ends: inferior portion of the cricoid cartilage
    • Leads to the esophagus
  • Lies posterior to the larynx → connects via the laryngeal inlet on the anterior wall
  • Piriform recesses (also called sinuses) are small cavities on either side of the laryngeal inlet.

Muscles of the pharynx

Constrictor muscles constitute the outer circular layer of muscle. During swallowing, constrictor muscles constrict to propel the food bolus downward.

• Superior constrictor muscle
• Middle constrictor muscle
• Inferior constrictor muscle

Longitudinal muscles constitute the inner muscular layer and play a role in elevating the pharynx and larynx during swallowing and speaking.

• Palatopharyngeus
• Stylopharyngeus
• Salpingopharyngeus

Fascia

There are 2 layers to the pharyngeal fascia:

• Buccopharyngeal fascia:
  • Thin
  • Overlays the outside of the muscle wall
• Pharyngobasilar fascia:
  • Thick
  • Lines the inner side of the muscle wall
  • Provides structure → helps maintain airway patency

Neurovasculature

• Arterial blood supply:
  • Tonsillar artery (branch of the facial artery)
  • Lingual artery
  • Ascending palatine artery
  • Descending palatine artery
  • Ascending pharyngeal artery
• Pharyngeal veins join to form a plexus that drains:
  • Superiorly → pterygoid plexus (infratemporal fossa)
  • Inferiorly → facial and internal jugular veins
• Lymph drains into the deep cervical nodes, which include:
  • Retropharyngeal nodes
  • Paratracheal nodes
  • Infrahyoid nodes
• Innervation from branches off of:
  • Vagus nerve (cranial nerve (CN) X)
  • Glossopharyngeal nerve (CN IX)

Microscopic Anatomy and Function

• Stratified squamous nonkeratinizing epithelium
• Lacks muscularis mucosa and submucosa
• The epithelium rests on the lamina propria containing a thick layer of longitudinally oriented elastic fibers (a useful diagnostic feature).
• The muscularis externa is composed of irregularly arranged skeletal muscle, which represents the longitudinal and constrictor muscles of the pharynx.
• Function and role in deglutition: swallowing → elevator skeletal muscles of the pharynx contract → pharynx raises and expands → receives bolus of food → elevator skeletal muscles of the pharynx relax → constrictor muscles of the pharynx contract → bolus is forced into the esophagus → initiation of peristalsis

Clinical Relevance

• Pharyngitis: inflammation of the pharynx. Affected individuals present with pain, irritation, discomfort, and dysphagia of the throat. Pharyngitis can result from bacterial or viral infections. If a viral infection is suspected, the treatment is often supportive with hydration and with the use of NSAIDs for pain. If a bacterial infection is suspected, antibiotics are used as 1st-line therapy.
• Diphtheria: a bacterial infection caused by Corynebacterium diphtheriae. A sheet of thick, gray material covering the posterior pharyngeal wall is the hallmark of diphtheria. Erythromycin is the 1st-line therapy for diphtheria; however, the infection can be prevented by vaccination.
• Zenker diverticulum: The inferior pharyngeal constrictor muscle subdivides into the thyropharyngeus and cricopharyngeus muscles. Intrapharyngeal pressure can increase and form a diverticulum if there is incoordination between the contraction and relaxation of these 2 muscles. The diverticulum serves as a reservoir for the accumulation of food and can lead to dysphagia. Other complications include gurgling, aspiration, foul breath, and the presence of a neck mass.
• Pharyngeal cancer: cancer of the tissues of the pharynx. Pharyngeal cancer includes cancer of the nasopharynx, oropharynx, and hypopharynx. Most pharyngeal cancers are squamous cell carcinomas. Common symptoms include sore throat, pain or difficulty swallowing, persistent ear pain, lump in the neck or throat, hoarseness or changes in voice, nosebleeds, headaches, coughing up of blood, unexplained weight loss, constant bad breath, and jaw stiffness. Pharyngeal cancer is treated with surgical resection.