Bronchiole

Recommended video: Bronchioles and alveoli [16:32]

Learn the fine structure of the lungs.

The bronchioles are part of conducting zone of the respiratory system. The conducting zone allows air to travel from the trachea into the alveoli, where gaseous exchange occurs.

The bronchioles start off as bronchi. The right and left main bronchi branch off from the trachea into the lungs. Subsequently, they further branch into smaller bronchi. Beyond the terminal segmental bronchi, the branches are referred to as bronchioles. The bronchioles can branch between 20-25 times.

There are two types of bronchioles:

• Conducting bronchioles: conduct air but they lack glands or alveoli
• Respiratory bronchioles: conduct air and also contain alevoli that extend from their lumens. Alveoli are the basic unit for gaseous exchange in the lungs. These bronchioles give rise to alveolar ducts that then give rise to alveolar sacs.

The bronchi contain cartilage plates. However, as they branch into bronchioles, the passageways narrow further. This means that bronchioles do not have cartilage plates within their walls. Instead, bronchioles have a thick layer of smooth muscle within their walls and are lined by cuboidal epithelium. 

Blood supply to the bronchioles is via the bronchial arteries that are distributed along and supply the bronchial tree.