respiratory bronchiole

The respiratory bronchiole is where the airway tree stops being mere plumbing and starts doing its real job. Lying just beyond the terminal bronchiole, its walls are dotted with occasional alveoli, so air passing through can already begin trading oxygen and carbon dioxide with blood.

This makes it the first part of the respiratory zone — the gas-exchanging territory of the lung. From here onward the airways branch into alveolar ducts and clusters of alveoli, and the wall becomes progressively more devoted to exchange and less to conduction.

Because gas exchange begins here, damage centred on the respiratory bronchiole has outsized consequences. Centrilobular (centriacinar) emphysema, the form most linked to cigarette smoking, characteristically destroys tissue around these airways first.