The pulmonary airway comprises those parts of the respiratory system through which air flows, conceptually beginning (on inhalation from the external environment) at the nose and mouth, and terminating in the alveoli. It is generally used synonymously with respiratory tract, to avoid sounding overly scientific.
From the mouth or nose, inhaled air passes through the pharynx into the trachea, where it separates into the left and right main bronchi at the carina, situated at the level of the second thoracic vertebra. The main bronchi then branch into large bronchioles, one for each lobe of the lung. Within the lobes, the bronchioles further subdivide some twenty times, ending in clusters of alveoli.
The epithelial surfaces of the airway contain cilia. Inhaled particles adhere to mucus secreted by goblet cells, which is continuously driven outwards by the cilia. The epithelium of the airway also secretes a watery fluid upon which the mucus can ride freely. The production of this fluid is impaired by the disease cystic fibrosis. Macrophages in the airways help promote prophylaxis and prevent infection and contamination, by engulfing bacteria and other inhaled particles.
Certain conditions require tracheal intubation (insertion of a tube) to secure the patency (openness) of the airway. Airway devices are used to assist in tracheal intubation.