The |bronchioles| are the intermediate ~air~ passages within the |lungs|. They branch off of the large bronchii and extend to the smaller branches of the alveolar ducts. Each respiratory |bronchiole| subdivides into five or more alveolar ducts. The structure of the bronchii, |bronchioles|, alveolar ducts, and |alveoli| is often called the "pulmonary tree" because its extensive branching resembles the limbs and leaves of a tall deciduous tree.
