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.