26.3
Pharynx
The pharynx, a tubular structure framed by skeletal muscle and lined with mucous membrane, extends continuously from the nasal cavities. It is segment…
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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Q1: What are the three main divisions of the pharynx?
The pharynx divides into three sections: the nasopharynx, oropharynx, and laryngopharynx. The nasopharynx is the upper segment behind the nasal cavity, lined with ciliated pseudostratified columnar epithelium. The oropharynx is the middle section serving as a shared pathway for air and food. The laryngopharynx is the lowest part, opening into both the esophagus and larynx.
Q2: How does the nasopharynx protect against pathogens?
The nasopharynx contains pharyngeal tonsils, or adenoids, which trap dust and pathogens from inhaled air. These lymphoid tissue clusters act as a reservoir of lymphocytes and are covered with ciliated epithelium that captures and eliminates pathogens. The ciliated pseudostratified columnar epithelium also propels mucus downward to remove trapped particles.
Q3: Why does the oropharynx and laryngopharynx have different epithelium than the nasopharynx?
The oropharynx and laryngopharynx are lined with nonkeratinized stratified squamous epithelium to withstand abrasion from food particles, unlike the nasopharynx's ciliated columnar epithelium. This epithelial shift occurs as the nasopharynx transitions into the oropharynx at the fauces. The stratified squamous tissue provides protection in areas where food and liquid pass through.
Q4: What role do the tonsils play in the oropharynx?
The oropharynx houses two sets of tonsils—palatine tonsils embedded in lateral walls and lingual tonsils posterior to the oral cavity. Both are composed of lymphoid tissue that captures and eliminates pathogens entering via oral or nasal cavities. These tonsils function as part of the immune system's first line of defense in the respiratory and digestive pathways.
Q5: How does the uvula prevent food from entering the nasal cavity?
The uvula, a small teardrop-shaped structure at the soft palate's peak, swings upward during swallowing along with the soft palate. This movement seals off the nasopharynx, preventing ingestion of materials into the nasal cavity. This reflex action ensures food and liquid travel only into the esophagus rather than the respiratory pathway.
Q6: Why do common colds often lead to ear infections?
The nasopharynx is linked to each middle ear cavity by auditory, or Eustachian, tubes. When pathogens from a common cold infect the nasopharynx, they can travel through these tubes and cause middle ear infections. This anatomical connection explains the frequent association between upper respiratory infections and ear complications.
Q7: Where does the pharynx begin and end in the respiratory tract?
The pharynx is approximately 13 centimeters long and extends from the internal nares, or nasal openings, down to the cricoid cartilage of the larynx. It serves as a continuous conduit from the nasal cavities through the three pharyngeal regions. At its lower end, the laryngopharynx opens anteriorly into the larynx while posteriorly leading into the esophagus.