The<unk> s are the first  airway branches that no longer contain cartilage. They are branches of the bronchi, and are smaller than one millimeter in diameter.
There are no glands or cartilage in any of the<unk> s, and the epithelial cells become more cuboidal in shape.
The<unk> s terminate by entering the circular sacs called alveoli.
Control of airflow resistance and air distrubution in the lungs is controlled by the<unk> s.
Bronchiole
Bronchus
Tracheal bronchus
Secondary bronchus
Alveolar duct
Tertiary bronchus
Bronchial veins
Pharynx