In a section of lung tissue consisting dominantly of alveoli, a tubule about 2mm in diameter is observed that contains smooth muscle and cailage in its wall. The tubule is which one of the following?
Any tubule with cailage in its wall and contained in the parenchyma of the lung is a bronchus. Alveolar ducts, alveolar sacs, and bronchioles do not contain cailage. The trachea lies outside of the lung.
Alveolar duct
Alveolar sac
Bronchiole
Bronchus