Terminal and repiratory bronchioles of the lung

The the lower airways that transport air into the lung parenchyme / the alveoli has to terminate somehow, and this happens at the terminal bronchioles, hence the name. After the air passes the terminal bronchioles, it flows through the respiratory bronchioles and finally into the alveoli.

Histologically, the terminal bronchiole primarily lacks alveoli, while the respiratory bronchiole contains scattered alveoli in its walls, facilitating gas exchange. The anatomical differences are easy to see in this image.