Pharynx

1. Overview

The pharynx is a muscular tube that forms part of both the respiratory and digestive systems. It serves as a shared passageway for air, food, and fluids, connecting the nasal cavity and oral cavity to the larynx and esophagus. Functionally, it plays a critical role in breathing, swallowing, and speech. It is divided into three anatomical regions: the nasopharynx, oropharynx, and laryngopharynx.

2. Location

The pharynx extends from the base of the skull (just posterior to the nasal cavity) to the level of the sixth cervical vertebra (C6), where it bifurcates into the esophagus (posteriorly) and larynx/trachea (anteriorly). It lies:

• Posterior to the nasal and oral cavities

• Anterior to the cervical spine

• Superior to the esophagus and larynx

3. Structure

The pharynx is approximately 12–14 cm long and composed of skeletal muscle layers lined by mucous membrane. It is subdivided into three regions:

Nasopharynx

• Located posterior to the nasal cavity and superior to the soft palate

• Communicates with the nasal cavity via the choanae

• Lined by respiratory epithelium

Oropharynx

• Posterior to the oral cavity, extending from the soft palate to the upper epiglottis

• Shared by the respiratory and digestive tracts

• Lined by non-keratinized stratified squamous epithelium

Laryngopharynx (Hypopharynx)

• Extends from the epiglottis to the cricoid cartilage (C6)

• Connects to the larynx anteriorly and esophagus posteriorly

• Lined by non-keratinized stratified squamous epithelium

Muscular Wall

Formed by:

• Constrictor muscles: Superior, middle, and inferior pharyngeal constrictors

• Longitudinal muscles: Stylopharyngeus, salpingopharyngeus, and palatopharyngeus

These muscles coordinate swallowing and maintain the structure of the pharyngeal wall.

Innervation

Provided via the pharyngeal plexus, formed by:

• Motor: Vagus nerve (CN X), except stylopharyngeus (glossopharyngeal, CN IX)

• Sensory: CN V2 (nasopharynx), CN IX (oropharynx), and CN X (laryngopharynx)

4. Function

The pharynx serves several important functions:

• Air conduction: Transports air from the nasal cavity to the larynx and trachea

• Swallowing: Propels food and liquids from the oral cavity to the esophagus

• Voice resonance: Acts as a resonating chamber contributing to speech sounds

• Protective reflexes: Triggers gag and cough reflexes to prevent aspiration

5. Physiological Role(s)

In addition to its mechanical functions, the pharynx plays roles in:

• Immune defense: Through lymphoid tissue (tonsils) in the naso- and oropharynx, forming Waldeyer’s ring

• Pressure equalization: Via the Eustachian tubes (nasopharynx) during swallowing and yawning

• Breathing coordination: Adjusts muscular tone to allow continuous airflow while preventing aspiration

• Speech modulation: Works with the larynx and oral cavity to produce articulate sounds

6. Clinical Significance

Pharyngitis

Inflammation of the pharynx, commonly caused by viral or bacterial infections (e.g., Group A Streptococcus). Symptoms include sore throat, fever, and dysphagia. Managed with supportive care or antibiotics when bacterial.

Obstructive Sleep Apnea (OSA)

Pharyngeal collapse during sleep leads to airway obstruction. Common in obese individuals or those with enlarged tonsils. Symptoms include snoring, daytime sleepiness, and gasping during sleep. Treated with CPAP, weight loss, or surgery.

Tonsillitis and Adenoid Hypertrophy

Enlarged tonsils (oropharynx) and adenoids (nasopharynx) can obstruct the airway or cause recurrent infections. Severe cases may require tonsillectomy or adenoidectomy.

Dysphagia (Swallowing Disorders)

Neuromuscular dysfunction or anatomical obstruction in the pharynx can impair swallowing, leading to aspiration, malnutrition, or pneumonia. Common in stroke patients and elderly.

Pharyngeal Cancer

Includes nasopharyngeal, oropharyngeal, and hypopharyngeal carcinomas. Risk factors include tobacco, alcohol, and HPV infection. Symptoms vary but may include:

• Sore throat

• Dysphagia

• Voice changes

• Neck lymphadenopathy

Diagnosis is via imaging and biopsy; treatment includes surgery, radiation, and chemotherapy.

Foreign Body Aspiration

Objects lodged in the pharynx may cause choking, pain, or obstruction. Immediate removal is necessary, especially in children.