Notes on the structure of the bronchus
In structure, the bronchi (sing bronchus) are similar to trachea; they are surrounded by incomplete hyaline cartilages lined with mucous membrane made up of ciliated columnar epithelium. The walls of the bronchi also have some smooth involuntary muscles. The bronchioles have a structure similar to bronchi but there are no cartilaginous structures; instead they consist of muscle fibres.
Copius mucous covers the epithelial lining and the action of the cilia pushes the mucous up to the larynx and pharynx from where it is either swallowed or thrown out. The mucous is secreted by the goblet cells which are present between the epithelial cells.