What marks the end of the conducting zone in the respiratory system?

The conducting zone of the respiratory system refers to the parts of the respiratory tract that are responsible for transporting air to the respiratory portions where gas exchange occurs, but do not participate in the actual exchange of gases. The terminal bronchioles are the last structures in this zone. They are the smallest air passages that still function solely to conduct air without involvement in gas exchange.

At the terminal bronchioles, the structure transitions into the respiratory zone, which begins with the respiratory bronchioles and includes the alveolar sacs where gas exchange takes place. This delineation is crucial because it highlights the functional differences between conducting airways that only facilitate airflow and the regions that enable the critical process of oxygen and carbon dioxide exchange. By understanding this, one can appreciate the organization of the respiratory system and its role in effective breathing and respiration.