What is the anatomy and function of the pharynx, larynx, and trachea?

Anatomy and Function of the Pharynx, Larynx, and Trachea

The pharynx, larynx, and trachea form a critical anatomical pathway that serves dual functions of respiration and deglutition, with specialized structures that protect the airway during swallowing while maintaining an open passage for breathing.

Pharynx Anatomy and Function

The pharynx is a U-shaped fibromuscular tube extending from the base of the skull to the cricoid cartilage, serving as a common aerodigestive tract 1. It is divided into three distinct regions:

1. Nasopharynx: The superior portion that connects to the nasal cavity
2. Oropharynx: The middle portion that connects to the oral cavity
3. Laryngopharynx (Hypopharynx): The inferior portion that connects to the larynx

The pharynx functions as:

• A passageway for air during respiration
• A food channel during swallowing
• A resonating chamber for speech production
• A protective structure with specialized reflexes

During swallowing, the pharynx undergoes a complex sequence of events lasting 1-2 seconds that protect the airway 2:

• The soft palate lifts to close off the nasopharynx
• The pharyngeal walls contract in a progressive wave to propel the bolus
• The tongue pushes backward and downward to provide positive pressure

Larynx Anatomy and Function

The larynx serves as the gateway between the upper and lower respiratory tracts 3 and consists of:

• Cartilaginous framework:

  • Thyroid cartilage (largest, forms the "Adam's apple")
  • Cricoid cartilage (forms a complete ring at the base)
  • Epiglottis (leaf-shaped cartilage that covers the laryngeal inlet during swallowing)
  • Paired arytenoid cartilages (control vocal fold movement)

• Vocal folds: Form the glottis, which is the narrowest part of the larynx

The larynx has three primary functions 1:

1. Airway protection: Acts as a protective valve to prevent aspiration
2. Respiration: Functions as an open valve during breathing
3. Phonation: Functions as a partially closed valve for voice production

The most sensitive regions of the airways for mechanically eliciting cough are the larynx and the tracheal and bronchial bifurcations 2, highlighting the protective role of these structures.

Trachea Anatomy and Function

The trachea extends from the lower edge of the cricoid cartilage to the carina where it divides into the mainstem bronchi 1, 4. Its key features include:

• Length of approximately 10-12 cm in adults
• Diameter of about 2-2.5 cm
• Composed of 16-20 U-shaped cartilaginous rings that provide structural support
• Posterior wall formed by the trachealis muscle (smooth muscle)

The trachea functions as:

• A conduit for air movement between the larynx and bronchi
• A protective structure with specialized mucociliary clearance mechanisms
• A flexible yet stable airway that accommodates neck movements

Integrated Function During Swallowing

During swallowing, these structures work in coordinated sequence 2:

1. The hyoid bone and larynx move upward and forward
2. The vocal folds adduct (move to midline)
3. The epiglottis folds over the arytenoid cartilages
4. The upper esophageal sphincter opens to allow passage of food
5. After the bolus passes, the sphincter closes to prevent regurgitation

This precise coordination prevents aspiration, which can lead to serious respiratory conditions including pneumonia 2.

Clinical Significance

Understanding the anatomy and function of these structures is critical for:

• Airway management: Proper placement of endotracheal tubes requires knowledge of the anatomical relationships 1
• Swallowing disorders: Dysphagia can result from impaired coordination of these structures 2
• Cough reflex: The cough reflex is mediated by sensory nerves in these structures and serves a vital protective function 2

Developmental Considerations

The anatomy of these structures changes significantly during development 2:

• Infants have a more superior laryngeal position
• The infant pharynx is shorter
• Infants can breathe and swallow simultaneously, an ability lost with maturity
• The adult pattern of swallowing muscle activation develops by ages 5-8 years

Understanding these anatomical and functional relationships is essential for clinicians managing patients with respiratory and swallowing disorders, as well as for performing procedures involving these structures.