The pharynx, a tubular structure framed by skeletal muscle and lined with mucous membrane, extends continuously from the nasal cavities. It is segmented into three major areas: the nasopharynx, oropharynx, and laryngopharynx.
Nasopharynx
The nasopharynx, bordered by the conchae of the nasal cavity, serves exclusively as an air conduit. In its superior region, the pharyngeal tonsils or adenoids are located. These tonsils are clusters of lymphoid reticular tissue akin to a lymph node. The precise function of the pharyngeal tonsil remains uncertain. Still, it is known to be a reservoir of lymphocytes and is covered with a ciliated epithelium that captures and eliminates pathogens inhaled during breathing. The pharyngeal tonsils are often large in children but tend to shrink or vanish with age. The uvula, a small teardrop-shaped structure at the peak of the soft palate, swings upward during swallowing, along with the soft palate, sealing off the nasopharynx and preventing ingestion of materials into the nasal cavity. In addition, the nasopharynx is linked to each middle ear cavity by auditory (Eustachian) tubes, explaining why common colds frequently lead to ear infections.
Oropharynx
The oropharynx, serving as a pathway for food and air, is bordered above by the nasopharynx and anteriorly by the oral cavity. The link between the oral cavity and the oropharynx is a passage known as the fauces. As the nasopharynx transitions into the oropharynx, the epithelium shifts from pseudostratified ciliated columnar to stratified squamous. The oropharynx houses two sets of tonsils—the palatine and the lingual tonsils—composed of lymphoid tissue that captures and eliminates pathogens entering the body via the oral or nasal cavities.
Laryngopharynx
Finally, the laryngopharynx, positioned below the oropharynx and at the back of the larynx, serves as a passageway for food and air until it reaches its lower end, where the digestive and respiratory systems split. The stratified squamous epithelium of the oropharynx extends into the laryngopharynx. The laryngopharynx opens anteriorly into the larynx, while posteriorly, it leads into the esophagus.
The pharynx or throat is about a 13 cm long tube extending from the internal nares down to the cricoid cartilage of the larynx.
It can be divided into the nasopharynx, oropharynx, and laryngopharynx.
The nasopharynx is the upper segment located behind the nasal cavity, extending to the soft palate.
It is lined with ciliated pseudostratified columnar epithelium, which helps propel the mucus downward.
The posterior wall of the nasopharynx contains the pharyngeal tonsil that traps dust and pathogens from the inhaled air.
The oropharynx, the middle section, is a shared pathway for air, food, and liquid that opens into the throat through the fauces.
It has two palatine tonsils embedded in lateral walls and two lingual tonsils posterior to the oral cavity.
The laryngopharynx, the lowest part, opens into the esophagus posteriorly and the larynx anteriorly at its lower end.
Both the oropharynx and laryngopharynx are lined with nonkeratinized stratified squamous epithelium to avoid abrasion from the food particles.
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