noses

The nose is the protruding facial feature that serves as the primary passage for air entering the respiratory system and houses the sense of smell. The external nose is composed of bone and cartilage and directs air into the nasal cavities.

Structurally, the external nose includes nasal bones at the upper part, paired cartilages shaping the tip and sides, and a midline septal cartilage. The internal nose consists of the nasal cavities separated by the nasal septum and lined with mucous membranes and ciliated epithelium. Turbinates (conchae) project into the airflow to increase surface area, aiding filtration, warming, and humidification. The roof houses the olfactory epithelium, where smell receptors reside.

Functions include respiration, filtration, humidification, and warming of inspired air; olfaction by sensory receptors in the olfactory epithelium; and voice resonance influenced by nasal cavities. Mucus traps particles and cilia move debris toward the pharynx for clearance.

Developmentally, the nose forms from the frontonasal prominence during embryogenesis; growth continues through childhood and puberty. Variation in size, shape, and septal alignment is common. Septal deviation can affect airflow and may be treated surgically or conservatively; nasal injuries are frequent.

Clinically, common nasal conditions include allergic rhinitis, sinusitis, and nasal polyps. Rhinoplasty and other procedures alter appearance or function. Across species, noses vary widely and underpin different olfactory capabilities, from highly sensitive noses in many mammals to comparatively subtler ones in humans.