Expansion
Trachea, main, lobar, segmental bronchi, then bronchioles, terminal and respiratory bronchioles, alveolar ducts and sacs
Expansion
- Trachea
- Main (primary) bronchi - one per lung
- Lobar (secondary) bronchi - 3 right, 2 left
- Segmental (tertiary) bronchi - 10 right, 8 to 10 left
- Conducting bronchioles
- Terminal bronchioles - the last purely conducting airway
- Respiratory bronchioles - the first with alveoli in their walls
- Alveolar ducts
- Alveolar sacs and alveoli
Two structural changes happen consistently as you descend: cartilage disappears (gone by the bronchiole), and the epithelium thins from pseudostratified columnar to simple squamous.
The terminal bronchiole is the boundary between the conducting and respiratory zones, and everything distal to a single terminal bronchiole is an acinus, the functional gas-exchanging unit.