For example, in humans, only a few cell types have motile cilia, namely sperm, epithelia cells in the bronchi and oviducts, and ependymal cells that line brain vesicles. But virtually all other ...

Cilia are small hairs which beat to push the mucus back up the trachea so it can be swallowed and destroyed in the stomach. Clean air then enters the two bronchi, one bronchus going to each lung.