Pharynx

The pharynx (also known as the throat) is a muscular, funnel-shaped organ located behind the oral and nasal cavities. It is about 5 - 5.5 inches (12 - 14 cm) long, depending on body size. 

The pharynx is an anatomical structure where both air and food passages intersect. Therefore it belongs to both the upper respiratory and gastrointestinal tracts.

It may be divided into three parts:

 

Innhaled air through the nose first reaches the nasopharynx, then the oropharynx, further flowing into the larynx via the laryngopharynx. On the other hand, food is transported from the oral cavity via the oropharynx and laryngopharynx into the esophagus.

The nasopharynx is the nasal part of the pharynx and its most upper part or superior division. It is located at the first and second cervical vertebrae level (C1 - C2), posterior and inferior to the nasal cavity. This part extends from the external cranial base to the free edge of the soft palate.

The upper part of the nasopharynx is firmly connected with the body of the sphenoid bone. The connection is known as the vault of the pharynx or pharyngeal fornix.

There is an opening in the wall of the nasopharynx that leads to the auditory tube, which connects the pharynx with the tympanic cavity (middle ear). 

The pharynx also houses lymphatic tissue masses called tonsils, including the:

  • Pharyngeal tonsil - located in the nasopharynx;
  • Two tubal tonsils (right and left) - located in the nasopharynx;
  • Two palatine tonsils (right and left) - located in the oropharynx;
  • Lingual tonsil - in the oropharynx.

 

Muscles of pharynx

The pharynx contains two groups of very well-developed paired skeletal muscles:

  • Circular muscles (constrictors) - muscles constricting the pharynx;
  • Longitudinal muscles (levators) - muscles that lift the pharynx.

Muscles of the pharynx, together with the tongue, soft palate, and larynx help to move and swallow the food as the soft palate elevates and closes the passage to the nasal cavity. The epiglottis depresses and closes the airways, allowing to move the food with the help of tongue and pharynx muscles further into the esophagus.

The circular or constrictor muscles are the following:

  • Superior pharyngeal constrictor
  • Medial pharyngeal constrictor
  • Inferior pharyngeal constrictor

The longitudinal or levator muscles include the following:

  • Stylopharyngeus 
  • Palatopharyngeus
  • Salpingopharyngeus

 

Neurovascular supply

The arterial blood supply for the pharynx is provided by the following vessels:

 

Venous drainage of the pharynx is provided by the pharyngeal (venous) plexus. It carries blood next to the facial and pharyngeal veins that further drain into the internal jugular vein.

 

The innervation of the pharynx is mainly provided by a network of nerves known as the pharyngeal plexus. It is created by the pharyngeal branches of the glossopharyngeal nerve (CN IX), vagus nerve (CN X) with additional fibers from the superior cervical ganglion of the sympathetic trunk.

  • The motor innervation is provided by the two mentioned cranial nerves. All pharyngeal muscles, except the stylopharyngeus muscle, are innervated by the pharyngeal branches of the vagus nerve. The stylopharyngeus muscle gets nerve supply from the same-named branches of the glossopharyngeal nerve.
  • The sensory nerve supply of the pharynx mainly comes from the glossopharyngeal nerve, however, the upper part of the nasopharynx is also innervated by branches of the maxillary nerve (CN V2).

 

Functions

Functions of the pharynx include:

  • Passage for the food and air
  • Peristalsis and food bolus moving, swallowing
  • Speech sound formation
  • Voice production and resonance
  • Participation in taste sensation creation
  • Air conditioning
  • Local immune responses
  • Defense against various harmful antigenes
  • Drainage of secretion from oral and nasal cavities and middle ear
  • Pressure equalization on both sides of the tympanic membrane