How do chemicals in cigarettes affect the cilia in the trachea?

Cigarette smoke irritates cells in the bronchi and this irritation triggers special cells to produce a layer of mucus designed to trap the foreign particles irritating the cells. This layer of mucus is then suppose to be swept away by the Cilia, though the tar found in cigarette smoke slows the action of the cilia. This tar accumulates in the mucus layer, because the cilia are not able to respond due to the presence of this tar. In conclusion, the mucus layer will gradually grow over time because the cilia will not be able to sweep away the accumulated foreign particles.