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Respiratory Bronchiole
Bronchial Tree

Respiratory Bronchiole

Bronchiolus respiratorius

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Quick Facts

The respiratory bronchiole is a short, thinner-walled branch of a terminal bronchiole; it differs from the other bronchioles in that its walls contain alveoli, in which gas exchange occurs. It further subdivides, subsequent branches becoming narrower in diameter and increasing in number of alveoli, with each branch terminating in an alveolar duct (Dorland, 2011).

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Respiratory bronchioles are formed by the branching of the terminal bronchioles. These bronchioles are considered part of the respiratory part of the respiratory tract, while the terminal bronchioles are considered part of the conducting portion of the respiratory tract.

Respiratory bronchioles are extremely thin. They have a similar histological appearance as the terminal bronchioles, however, in the smaller respiratory bronchioles, ciliated cells are absent (Ovalle et al., 2013).

Small out pockets of thin-walled alveoli bud from the respiratory bronchioles, between the smooth muscle fibers. These alveoli have a simple squamous epithelium.

Anatomical Relations

Respiratory bronchioles are located distal to the terminal bronchioles. They give rise to alveolar ducts and alveoli.


Dorland, W. (2011) Dorland's Illustrated Medical Dictionary. 32nd edn. Philadelphia, USA: Elsevier Saunders.

Ovalle, W. K., Nahirney, P. C. and Netter, F. H. (2013) Netter's Essential Histology. ClinicalKey 2012: Elsevier Saunders.

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