Anatomy of Respiratory System I: Upper Respiratory Tract

The upper respiratory tract comprises the nose, nasal cavity, oral cavity, paranasal sinuses, and pharynx. The nose and nasal cavity form the external opening for the respiratory tract, while the paranasal sinuses are four air-filled cavities surrounding the nasal cavity. The pharynx, or throat, connects the nasal cavity to the larynx and serves as a pathway for air and food.

Turbinates are three bony projections inside the nasal cavity that significantly increase the surface area of the nasal mucosa. This expanded surface area enhances the cavity's ability to warm and moisten incoming air before it reaches the lungs. The turbinates also help trap dust, pathogens, and other particles, preventing them from entering the lower respiratory tract.

The four paranasal sinuses are the frontal sinuses above the eyebrows, ethmoid sinuses between the eyes, sphenoid sinuses deep in the skull, and maxillary sinuses under the eyes in the cheekbones. These air-filled cavities are lined with ciliated pseudostratified columnar epithelium that warms, moistens, and filters air. They also lighten the skull and contribute to voice resonance.

The pharynx acts as a crossroads for the respiratory and digestive tracts, efficiently managing the passage of air and food to their respective destinations. It comprises three regions: the nasopharynx, oropharynx, and laryngopharynx. The laryngopharynx extends from the hyoid bone to the cricoid cartilage, directing air toward the larynx and food toward the esophagus.

The oral cavity acts as an alternative entry point for air, especially during intense physical activity or when the nasal passage is obstructed. Although it does not filter, warm, or humidify air as effectively as the nasal cavity, it remains an important secondary pathway for respiration when needed.

The pharynx contains lymphoid tissue, including the tonsils and pharyngeal tonsils, which help protect the body from pathogens entering through the mouth and nose. The oropharynx plays an essential role in the initial immune response to inhaled or ingested pathogens. This strategic location and lymphoid tissue involvement make the pharynx a critical first line of defense.

Sinusitis, an inflammation or infection of the paranasal sinuses, can cause pain, congestion, and impaired breathing. This condition highlights the importance of these sinuses in respiratory health and facial structure integrity. When sinusitis occurs, the normal filtration and humidification functions of the sinuses are compromised, affecting overall respiratory function.