9.7. Airways

Types of Airway

The respiratory tract can be divided into two parts: the respiratory airways and the conductive airways.

Respiratory airways
This is where gas exchange occurs. Specifically, these are the respiratory bronchioles, alveolar ducts and alveolar sacs.

Conducting airways
These provide a passageway to the alveoli. The components of the conducting airways are the trachea, bronchi, bronchioles and terminal bronchioles. The accompanying notes and diagram show the structure of the alveoli and their relationship with the bronchioles.

A trip through the airways
Trachea >> Primary bronchi >> Secondary bronchi >> Tertiary bronchi >> Bronchioles >> Terminal bronchioles >> Respiratory bronchioles >> Alveolar ducts >> Alveoli, grouped together to form an alveolar sac.

Additional Notes

  • The bronchioles do not contain cartilage. However, they contain smooth muscle fibres (arranged in circles), allowing constriction and dilation depending on the oxygen requirement of the body.
  • The bronchioles are less than 1mm in diameter.
  • Respiratory bronchioles give rise to alveolar ducts, which open into clusters of alveoli called alveolar sacs. Each alveolus is surrounded by a dense network of capillaries where gas exchange occurs. Oxygen diffuses from the alveolar lumen into the capillary blood, while carbon dioxide diffuses from the capillary blood into the alveolar lumen (where it will be removed during expiration).