The human nose serves as the primary entry point for air into the respiratory system. Among these components, the external nares represent the visible, outermost openings of the nasal cavity. These paired openings initiate the pathway for air to enter the body, setting the stage for further processing within the nasal passages.
Defining the External Nares
External nares, commonly recognized as nostrils, are the two distinct, symmetrical openings positioned at the base of the nose, directly above the upper lip. These openings serve as the visible gateway to the intricate nasal cavity. Each nare is precisely formed by the alar cartilages, which provide structural support and define their characteristic shape and flexibility.
The internal surfaces of the nares are initially lined with skin containing sebaceous glands and hair follicles, before smoothly transitioning into the specialized respiratory epithelium of the nasal mucosa deeper within the cavity. A cartilaginous and bony partition, known as the nasal septum, centrally divides the two external nares, ensuring separate and independent air pathways into each side of the nasal cavity.
The surrounding soft tissues, including small muscles, allow for subtle, involuntary movements of the external nares. These muscles can slightly adjust the diameter of the openings, optimizing airflow during different respiratory demands. Their prominent location on the face is strategically advantageous, enabling the efficient capture of air from the surrounding environment while also serving as a protective barrier for the internal nasal passages.
Key Functions of the External Nares
The external nares serve as the primary gateway for air to enter the human respiratory system. Through these openings, atmospheric air is drawn into the nasal cavity during inhalation.
Beyond simply allowing air passage, the external nares also play a significant role in the sense of smell, or olfaction. As air enters, it carries volatile odorant molecules that travel upwards towards the olfactory epithelium located in the superior part of the nasal cavity. There, these molecules dissolve in the moist mucus, stimulating specialized olfactory receptors and transmitting signals to the brain for interpretation. This initial entry point is therefore indispensable for the perception of scents, which profoundly influences taste perception, aids in identifying potential dangers, and provides important information about the surrounding environment.
The external nares further contribute to the initial conditioning of inhaled air, preparing it for the sensitive tissues of the lower respiratory tract. Hairs, known as vibrissae, are located just inside the openings and act as a coarse filter, physically trapping larger dust particles, pollen, and other airborne debris before they can proceed deeper into the respiratory system. This preliminary mechanical filtration helps protect the delicate respiratory tract from potentially harmful foreign matter and irritants.
Furthermore, as air passes through the narrow passages created by the external nares and into the nasal cavity, it immediately begins to be warmed and humidified. The extensive vascular network and moist mucous membranes lining the internal surfaces just beyond the nares contribute significantly to this process. This conditioning ensures that air reaching the delicate lung tissues is closer to body temperature and saturated with water vapor, preventing desiccation and facilitating efficient gas exchange across the alveolar membranes.