Respiratory bronchioles
Bronchioli respiratorii
Transitional airways (generations ≈17–19) whose walls are interrupted by scattered alveoli — the first site where gas exchange occurs.
Overview
Each terminal bronchiole divides into two or more respiratory bronchioles. Their walls are lined by cuboidal epithelium with club cells and occasional ciliated cells, interrupted by an increasing number of alveolar outpouchings along their length; the alveolar openings are lined by type I and II pneumocytes. Sparse smooth muscle and elastic fibres remain.
Respiratory bronchioles are where inhaled particles of ≈1–5 µm tend to deposit (by sedimentation), and they are the initial site of damage in smokers (respiratory bronchiolitis with pigmented macrophages) and coal workers.
- Location
Within the pulmonary acinus, between terminal bronchioles and alveolar ducts.
Anatomy
- Histology
Cuboidal epithelium (club cells, few ciliated cells) alternating with alveolar epithelium; sparse smooth muscle.
Function
- Conduct air into the alveolar ducts.
- Begin gas exchange through alveoli in their walls.
Clinical significance
Centriacinar emphysema
Smoking-related emphysema starts in the respiratory bronchioles at the centre of the acinus, sparing distal alveoli, and is most severe in the upper lobes. Coal workers' pneumoconiosis produces coal macules around respiratory bronchioles.
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.