Corpus: Pharynx

The pharynx is a shared pathway for the respiratory and digestive tracts. It is located behind the oral and nasal cavities and extends from the base of the skull to the esophagus and trachea. Structurally, it is a fibromuscular tube measuring approximately 12 to 15 cm in length.

The pharynx starts just below the sphenoid bone at the base of the skull and extends as a tube posterior to the nasal and oral cavities, reaching the level of the cricoid cartilage. It is divided into three sections, though their boundaries are not sharply defined:

• Nasopharynx (Epipharynx): The upper part, extending to about the level of the soft palate (velum).
• Oropharynx (Mesopharynx): The middle part, reaching down to the tip of the epiglottis.
• Laryngopharynx (Hypopharynx): The lower part, located behind the larynx and extending to the cricoid cartilage.

The lateral and posterior walls of the pharynx are composed of pharyngeal muscles, including the superior, middle, and inferior pharyngeal constrictor muscles. These muscles, collectively called the pharyngeal constrictor muscle, connect caudally with the esophagus. Clinically important regions, such as Killian's triangle and Laimer's triangle, are located where the pharyngeal muscles transition to the esophageal muscles. These areas are structurally weaker and may allow the formation of Zenker's diverticulum.

2.1. Nasopharynx (Epipharynx)

The roof of the nasopharynx houses the pharyngeal tonsil, part of the Waldeyer’s pharyngeal ring. Additionally, lymphatic tissue located in the lateral walls is referred to as the lateral cord.

The auditory tube (Eustachian tube) opens into the nasopharynx via the ostium of the tube, surrounded by a raised structure called the tubal protuberance. This opening plays a role in equalizing pressure between the middle ear and the nasopharynx. Below the tubal protuberance, another elevation called the levator cushin is formed by fibers of the levator veli palatini muscle. The paired tubal tonsils are located near the tube opening. Behind the torus tubarius is a blind-ending space called the pharyngeal recess (Rosenmüller’s fossa), which serves as an important landmark for medical procedures involving the auditory tube.

2.2. Oropharynx (Mesopharynx)

The oropharynx is open to the oral cavity and begins at the level of the soft palate. It includes structures such as the uvula and the edges of the soft palate, which form the boundary between the oral cavity and the pharynx. The constrictor muscles of the pharynx begin in this region and are anchored to the atlantooccipital membrane. On its dorsal side, these muscles are joined by a connective tissue seam known as the pharyngeal raphe.

2.3. Laryngopharynx (Hypopharynx)

The laryngopharynx is located above and behind the larynx, extending down to the upper edge of the cricoid cartilage, where it transitions into the esophagus. Below the epiglottis, the respiratory and digestive pathways diverge: the airway continues into the larynx and trachea, while the digestive pathway leads into the esophagus.

2.4. Vascular supply

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

• Ascending pharyngeal artery (from the external carotid artery)
• Superior thyroid artery (from the external carotid artery)
• Inferior thyroid artery (from the thyrocervical trunk of the subclavian artery)
• Ascending palatine artery (from the facial artery)
• Descending palatine artery (from the maxillary artery)

Venous drainage occurs through the pharyngeal venous plexus, which empties directly or indirectly into the internal jugular vein.

2.5. Innervation

The pharynx is richly innervated, with sensory and motor fibers derived from the cranial nerves and the autonomic nervous system. The glossopharyngeal nerve (cranial nerve IX) predominantly innervates the upper pharynx, while the vagus nerve (cranial nerve X) supplies the lower portions. Sympathetic innervation is provided by fibers from the superior cervical ganglion.

The upper part of the nasopharynx is lined with ciliated pseudostratified columnar epithelium (respiratory epithelium) that includes goblet cells and kinocilia. In contrast, the mucosa of the oropharynx and laryngopharynx is lined with non-keratinized stratified squamous epithelium. This epithelium transitions seamlessly into the esophageal mucosa without a distinct boundary.

Beneath the epithelial layer lies a thin layer of connective tissue, which is surrounded by striated muscle. These muscles are primarily derived from the embryonic pharyngeal arches and are under visceromotor control, meaning they are not entirely subject to voluntary control.

The pharynx is the connection between the nasal cavity and the trachea, as well as between the oral cavity and the esophagus. In this region, the respiratory and digestive pathways intersect.

During swallowing, the pharyngeal muscles contract to transport chewed food downward toward the esophagus. At the same time, these contractions pull the epiglottis over the opening of the larynx, effectively sealing it off and preventing food or liquid from entering the airway. This coordination helps prevent aspiration of food particles into the respiratory tract.

The pharynx is a site of origin for different diseases. Common conditions include pharyngitis and tonsillitis, while more severe diseases, such as diphtheria, can obstruct the airway and pose a life-threatening risk. Additionally, structural abnormalities like Zenker’s diverticulum or congenital cysts (e.g., Tornwaldt cyst) can affect the pharynx. The pharynx also serves as an entry point for pathogens, making it susceptible to infectious diseases.

• 3D model brachial plexus - anatomical site; Dr Claudia Krebs (Faculty Lead) University of British Columbia