Makindo Medical Notes

Anatomy of the Pharynx

The pharynx is a muscular tube that connects the nasal and oral cavities to the larynx and esophagus. It serves as a common pathway for both air and food. The pharynx is approximately 12-14 cm long and is divided into three main sections: the nasopharynx, oropharynx, and laryngopharynx. It plays a vital role in the processes of breathing, swallowing, and vocalization.

Divisions of the Pharynx

• Nasopharynx:
  • Located posterior to the nasal cavity and superior to the soft palate.
  • Serves as a passage for air from the nasal cavity to the oropharynx.
  • Contains the pharyngeal tonsils (adenoids) and the openings of the Eustachian tubes, which connect to the middle ear and help equalize pressure.
• Oropharynx:
  • Located posterior to the oral cavity and extends from the soft palate to the level of the hyoid bone.
  • Acts as a pathway for both air and food. During swallowing, the soft palate rises to prevent food from entering the nasopharynx.
  • Contains the palatine tonsils and the lingual tonsils.
• Laryngopharynx (Hypopharynx):
  • Located posterior to the larynx and extends from the hyoid bone to the esophagus.
  • Functions as a pathway for food and air. Air passes into the larynx, while food is directed toward the esophagus.
  • At the junction of the laryngopharynx, the epiglottis plays a key role in preventing food from entering the airway by covering the laryngeal inlet during swallowing.

Muscles of the Pharynx

The pharynx is made up of several muscles that aid in the processes of swallowing and speech. These muscles can be divided into two main groups: the constrictor muscles and the longitudinal muscles.

• Constrictor Muscles:
  • Superior Constrictor: Helps in constricting the upper part of the pharynx during swallowing.
  • Middle Constrictor: Constricts the middle portion of the pharynx.
  • Inferior Constrictor: Constricts the lower portion of the pharynx and is involved in pushing food into the esophagus.
• Longitudinal Muscles:
  • Stylopharyngeus: Elevates the pharynx during swallowing and speech.
  • Palatopharyngeus: Helps in narrowing the pharyngeal cavity and elevating the larynx during swallowing.
  • Salpingopharyngeus: Assists in elevating the pharynx and opens the Eustachian tube during swallowing.

Blood Supply of the Pharynx

• Arteries:
  • Supplied primarily by branches of the external carotid artery, including the ascending pharyngeal artery, the facial artery, and the maxillary artery.
• Veins:
  • The venous drainage is via the pharyngeal plexus, which drains into the internal jugular vein.

Nerve Supply of the Pharynx

• Motor Innervation:
  • All pharyngeal muscles, except the stylopharyngeus (which is supplied by the glossopharyngeal nerve, CN IX), are innervated by the pharyngeal branch of the vagus nerve (CN X).
• Sensory Innervation:
  • The nasopharynx is innervated by the maxillary branch of the trigeminal nerve (CN V).
  • The oropharynx is innervated by the glossopharyngeal nerve (CN IX).
  • The laryngopharynx is innervated by the vagus nerve (CN X).

Functions of the Pharynx

• Swallowing (Deglutition): The pharynx plays a key role in swallowing by moving food from the mouth to the esophagus. The constrictor muscles contract in a coordinated sequence to propel food downwards.
• Respiration: The pharynx is part of the respiratory system, allowing air to pass from the nasal and oral cavities to the larynx and trachea.
• Speech: It aids in speech production by resonating sound waves that come from the larynx.
• Immune Function: The tonsils, particularly the palatine, pharyngeal, and lingual tonsils, form part of the immune system and help in defending against infections by trapping pathogens entering through the mouth or nose.