Pharynx

The pharynx is a component of the digestive system that lies posterior to the nasal cavity, oral cavity, and larynx. The pharynx can be divided into the oropharynx, nasopharynx, and laryngopharynx. Pharyngeal muscles play an integral role in vital processes such as breathing, swallowing, and speaking. The muscles of the pharynx receive innervation from the vagus and glossopharyngeal nerve to propel food from the oral cavity into the esophagus.

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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.
Pharynx arises from the pharyngeal arches

The pharynx arises from the pharyngeal arches:
Pharyngeal pouches are located on the inside of the pharynx (yellow outline), whereas pharyngeal clefts are located on the outside of the pharynx (green outline). The muscles of the pharynx are derived from the 4th and 6th pharyngeal arches.

Image by Lecturio.

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.
Sagittal view of the head and neck showing the location of the pharynx and its anatomical landmarks

Sagittal view of the head and neck showing the location of the pharynx and its anatomical landmarks

Image: “2303 Anatomy of Nose-Pharynx-Mouth-Larynx” by OpenStax College. License: CC BY 3.0, edited by Lecturio.

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.
Sagittal view of the head and neck displaying the division of the pharynx

Sagittal view of the head and neck showing the division of the pharynx

Image: “2411_Pharynx” by Phil Schatz. License: CC BY 4.0

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
Table: Constrictor muscles of the pharynx
Muscle Origin Insertion Neurovasculature
Superior constrictor muscle
  • Pterygomandibular raphe
  • Medial pterygoid plate
  • Posterior end of the mylohyoid line of mandible
  • Pharyngeal tubercle of the occipital bone
  • Pharyngeal raphe
Blood supply:
  • Ascending pharyngeal artery
  • Tonsillar branch of the facial artery

Innervation:
Pharyngeal plexus of the vagus nerve
Middle constrictor muscle
  • Hyoid bone
  • Stylohyoid ligament
Pharyngeal raphe Blood supply:
Ascending pharyngeal artery

Innervation:
Pharyngeal branch of the vagus nerve (CN X) and pharyngeal plexus
Inferior constrictor muscle
  • Oblique line of the thyroid cartilage
  • Cricoid cartilage
Cricopharyngeal part encircles the pharyngoesophageal junction without forming a raphe. Blood supply:
  • Pharyngeal branch of the ascending thyroid artery
  • Muscular branches of the inferior thyroid artery

Innervation:
Pharyngeal branch of the vagus nerve (CN X) and pharyngeal plexus
CN: cranial nerve
Table: Longitudinal muscles of the pharynx
Muscle Origin Insertion Neurovasculature
Palatopharyngeus
  • Posterior border of the hard palate
  • Palatine aponeurosis
Posterior border of the lamina of the thyroid cartilage and side of the pharynx and esophagus Blood supply:
Facial artery

Innervation:
Pharyngeal branch of the vagus nerve (CN X) and pharyngeal plexus
Stylopharyngeus Styloid process of the temporal bone Posterior border of the thyroid cartilage Blood supply:
Pharyngeal branch of the ascending pharyngeal artery

Innervation:
Glossopharyngeal nerve
Salpingopharyngeus Cartilaginous part of the Eustachian tube Posterior and superior borders of the thyroid cartilage with the palatopharyngeus Blood supply:
Ascending pharyngeal artery
Innervation:
Glossopharyngeal nerve (CN IX)
CN: cranial nerve
The constrictor and longitudinal muscles of the pharynx

Constrictor and longitudinal muscles of the pharynx

Image by Lecturio.

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
The role of the pharynx during the deglutition process

Image showing the role of the pharynx during the deglutition process

Image: “2413 DeglutitionN” by OpenStax College. License: CC BY 3.0

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.

References

  1. Drake, R.L., et al. (2020). Chapter 8: Regional Anatomy, Pharynx. In Gray’s Anatomy for Students, 4th ed. Pages 1029-1041. Churchill Livingstone/Elsevier.
  2. Moore, K.L., Dalley, A.F., Agur, A.M.R. (2014). Chapter 8: Neck. In Clinically Oriented Anatomy, 7th ed. Pages 1032-1038. Lippincott Williams & Wilkins, a Wolters Kluwer business.
  3. Albahout, K. (2021). Anatomy, Head and Neck, Pharynx. Retrieved Sep 19, 2021, from https://www.statpearls.com/ArticleLibrary/viewarticle/36358
  4. Bui, T. (2021). Anatomy, Head and Neck, Pharyngeal Muscles. Retrieved Sep 19, 2021, from https://www.statpearls.com/ArticleLibrary/viewarticle/27102

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