Anatomy of the Nasal Cavity
The nasal passages are aerodynamic structures that function as a filter and air-conditioner to protect the lower airways. This functionality is achieved by the complex, narrow geometry of the nose. Large particles are efficiently filtered out and infective agents are presented to the abundant nasal immune system. The nose is specialized to warn and protect us against dangers, but it is also a delicate sensory organ designed to provide us with the greatest pleasures in life.
The inside of the nose is lined with highly vascularized mucosa, which provides a first line of defense against harmful particles. Between the anterior third of the nose – roughly the externally visible part – and the posterior two thirds – deep inside the head above the roof of the mouth – the nasal valve disrupts inhaled airflow to trap airborne particles in the nasal secretions. Particles are deposited on the mucosa in the valve from where the mucociliary transport mechanism carries them backwards to eventually be swallowed.
Beyond the nasal valve, the nasal cavity is divided into slit-like passages by the nasal turbinates and lined by a single cell-thick columnar epithelium. Slowing of the airflow as it passes over the turbinates allows time for inhaled air to be warmed and moistened, within fractions of a second, before reaching the lungs.