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Respiratory Mucosa
Bronchial Tree

Respiratory Mucosa

Tunica mucosa respiratoria

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Quick Facts

The mucosa is the mucous lining of various hollow structures, facing the lumen, comprising, in many locations, the epithelium, basement membrane, lamina propria mucosae, and lamina muscularis mucosae (Dorland, 2011).

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The mucosa of the bronchioles is composed of epithelium with a variety of cellular populations. As segmental bronchi branch into terminal bronchioles, there is a gradual change in the epithelium from a pseudostratified ciliated epithelium with goblet cells to a simple cuboidal epithelium that may be ciliated. The number of ciliated and goblet cells decline in numbers and goblet cells end up being replaced by the Clara cells (Ovalle et al., 2013).

As the mucosal layer of the terminal bronchioles extends into the respiratory bronchioles, the cellular composition remains similar, primarily consisting of ciliated cuboidal cells with a reduced number of Clara cells. The respiratory mucosal layer is thrown into folds due to the constriction of the overlying smooth muscle fibers.

Anatomical Relations

The mucosa of the intrapulmonary bronchial tree forms the inner layer on the bronchiole. From deep to superficial, it is composed of its outer epithelium resting on a basement membrane and a lamina propria. The mucosa is surrounded by a submucosa, containing smooth muscle that surrounds it in a spiraled fashion.


The mucosa is vital in protecting the lungs from environmental insults and maintaining homeostasis.

The ciliated cells are responsible for beating synchronously, sending foreign particles and mucus back up to the bronchi.

Clara cells are described as a bronchiolar-specific stem cell population paramount to protecting the airways from environmental hazards and are involved in maintaining lung homeostasis.

Brush cells (tuft, caveolated, multivesicular or fibrillovesicular) have also been identified in the bronchioles. These brush cells present microvilli on their apical surfaces and are responsible for absorption, chemosensing, and repair after mucosal injury (Reid et al., 2005).


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.

Reid, L., Meyrick, B., Antony, V. B., Chang, L. Y., Crapo, J. D. and Reynolds, H. Y. (2005) 'The mysterious pulmonary brush cell: a cell in search of a function', Am J Respir Crit Care Med, 172(1), pp. 136-9.

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