The nostril is the primary entrance for air into the human respiratory system. It acts as a gateway, beginning the process of preparing inhaled air before it reaches the lungs.
The Visible Entrance
The first area inside the nostril is the nasal vestibule, a small, dilated space. This entryway is lined with skin. Coarse hairs, known as vibrissae, are visible within the vestibule and serve as a preliminary filter.
The nasal vestibule also contains sebaceous glands, which produce an oily substance that helps keep the area moist and trap particles. The anterior part of the nasal septum, the wall dividing the two nostrils, is also visible here. This section of the nose initiates the process of air preparation.
Deeper Within the Nasal Cavity
Beyond the vestibule, the nasal cavity is a space divided into two sides by the nasal septum. Curved shelves of bone called turbinates project from the lateral walls. There are three turbinates on each side: the superior, middle, and inferior, which create distinct air passages. These structures are covered by a thick layer of mucous membrane.
The majority of the nasal cavity is lined by specialized respiratory mucosa, which appears pinkish. This mucosa consists of ciliated pseudostratified columnar epithelium, equipped with tiny, hair-like projections called cilia. Interspersed among these ciliated cells are goblet cells, which are shaped like wine goblets and produce mucus. This mucus forms a protective layer, trapping particles.
High within the nasal cavity lies the olfactory mucosa. This specialized tissue appears slightly thicker and yellowish-brown. The olfactory mucosa contains specialized nerve endings that are responsible for the sense of smell. The nasal cavity also has a rich blood supply, which contributes to its functions, and nerve endings for general sensation.
The Essential Functions
The structures within the nostril and nasal cavity work together to perform several functions for respiration and sensation. Air first enters through the nostrils, where the vibrissae in the nasal vestibule act as a coarse filter, trapping larger particles. This initial filtration prevents many foreign substances from reaching deeper into the respiratory tract.
As air moves past the vestibule, it encounters the extensive surface area provided by the turbinates and the lining of the nasal cavity. The rich blood supply within the nasal mucosa helps to warm the inhaled air, bringing it close to body temperature. Simultaneously, moisture evaporates from the mucosal lining, humidifying the air to nearly one hundred percent humidity.
The mucus produced by goblet cells in the respiratory mucosa traps smaller airborne particles, allergens, and microorganisms that bypass the nasal hairs. The cilia on the respiratory epithelial cells then rhythmically sweep this mucus, along with the trapped debris, towards the back of the throat. This mucociliary clearance mechanism directs the contaminated mucus to be swallowed and neutralized by stomach acids, preventing these particles from entering the lungs.
Beyond air conditioning, the specialized olfactory mucosa located high in the nasal cavity detects odor molecules, allowing for the sense of smell. This sensory capability is important for identifying scents and contributes significantly to the perception of taste.