Alveolar ducts of the lung (100X)

The terminal bronchiole always split into two respiratory bronchioles. As you now might already know, respiratory bronchioles have alveoli as part of the wall.  The epithelium lining the wall consists of a single columnar or cuboidal epithelium with cells with cilia and club cells.

The alveolar duct connects the respiratory bronchioles to the alveolar sacs. The alveolar ducts consist of a series of small tube-like passages that have walls composed of alveoli.