What are the small air passages that lead into the alveolar ducts called?

The small air passages that lead into the alveolar ducts are referred to as respiratory bronchioles. These structures are a part of the respiratory zone of the lungs, responsible for gas exchange. Unlike terminal bronchioles, which are part of the conducting zone and do not contribute to gas exchange, respiratory bronchioles have the capability to facilitate this process due to the presence of alveoli along their walls.

The significance of respiratory bronchioles lies in their transitional role in the respiratory tract. As air flows from the larger bronchi to the terminal bronchioles and then into the respiratory bronchioles, this progression marks the shift from purely conducting airways to areas where respiration occurs. The respiratory bronchioles branch into alveolar ducts, which ultimately lead to the alveolar sacs where the majority of gas exchange happens. This anatomy is essential for the efficient functioning of the respiratory system, enabling oxygen to enter the bloodstream and carbon dioxide to be expelled.