Fig 13. Lung (NO-6-b)
The respiratory bronchiole (RB) has a wall composed of two
portions of different thickness. The most distal component of
the respiratory passage is the alveolus. Groups of alveoli are
clustered together sharing a common opening and are
referred to as the alveolar sac (AS). Alveoli that form a tube
are referred to as alveolar ducts (AD).