The nose is the most prominent feature of the human face and serves as the primary entrance to the respiratory tract. Beyond its aesthetic role, it acts as a sophisticated processing unit for incoming air. It warms, humidifies, and filters air before it reaches the delicate tissues of the lungs. Additionally, the nose houses the peripheral organs for the sense of smell, contributing significantly to taste perception and environmental hazard detection. Structurally, it is divided into an external portion projecting from the face and an internal nasal cavity separated into two halves by the nasal septum.
The external nose is framed by bone and cartilage, giving it both rigidity and flexibility. The upper bony bridge is formed by the nasal bones, while the lower flexible portion relies on various hyaline cartilages, including the lateral processes and the major alar cartilages. Inside, the nasal cavity opens anteriorly through the nares and communicates posteriorly with the nasopharynx via the choanae. The lateral walls feature three bony shelves known as nasal conchae or turbinates (superior, middle, and inferior), which create turbulent airflow to maximize contact between the air and the mucosal surface.
The paranasal sinuses are air-filled cavities located in the bones surrounding the nasal cavity: the frontal, sphenoid, ethmoid, and maxillary bones. They all drain into the nasal cavity through small openings called ostia. These sinuses lighten the weight of the skull, resonate the voice, and produce mucus that helps keep the nasal passages moist. Because their drainage pathways are narrow, they are prone to blockage during upper respiratory infections, leading to painful pressure and inflammation known as sinusitis.
As air enters the nasal cavity, rapid physical changes occur to protect the lower respiratory system. The rich vascular network in the lamina propria acts like a radiator, warming cold air close to body temperature. Simultaneously, moisture evaporating from the mucous lining humidifies the air, preventing the delicate alveolar membranes from drying out. Large dust particles and foreign debris are filtered out by coarse hairs in the vestibule, while smaller particles stick to the sticky mucus blanket and are cleared away by ciliary action.
Olfaction begins in the roof of the nasal cavity within a specialized area of epithelium. Specialized bipolar olfactory receptor neurons possess cilia that extend into the mucous layer, where odorant molecules dissolve and bind to specific receptor proteins. When stimulated, these receptors send electrical signals along their axons, which pass upward through the cribriform plate of the ethmoid bone to synapse in the olfactory bulb. From there, neural pathways project directly to the limbic system and cortex, linking smells deeply to memory and emotion.
The nose is frequent site of clinical conditions ranging from minor annoyances to life-threatening emergencies. Epistaxis, or nosebleed, most commonly originates from Kiesselbach's plexus on the anterior nasal septum, a fragile vascular network easily traumatized by picking or dry air. Allergic rhinitis causes sneezing, congestion, and clear rhinorrhea due to an IgE-mediated immune response to environmental allergens. Furthermore, nasal polyps—noncancerous growths resulting from chronic inflammation—can obstruct airflow and diminish the sense of smell.