Mucosa of bronchus

The bronchial mucosa is the innermost lining of the bronchi, composed of two principal layers: the surface epithelium and the underlying lamina propria, separated by a basement membrane.

Epithelial Layer

The bronchial epithelium is a pseudostratified, ciliated columnar epithelium containing multiple cell types:

• Ciliated cells the most abundant luminal cell type (~61% of epithelial volume along with nonsecretory luminal cells), responsible for mucociliary clearance

• Goblet (mucous) cells secrete mucus glycoproteins (mucins) that trap inhaled particles and pathogens; comprise approximately 6% of epithelial volume in healthy individuals

• Basal cells progenitor cells that rest on the basement membrane and do not reach the lumen; account for roughly 32% of epithelial volume and serve as stem cells for epithelial renewal

• Neuroendocrine (Kulchitsky) cells rare, basally located cells containing densecore granules with neuroactive substances

• Clara (club) cells found predominantly in the smaller bronchioles, contributing to secretory and detoxification functions

Basement Membrane

Beneath the epithelium lies the basement membrane, which includes a lamina reticularis (reticular basement membrane) with a median thickness of approximately 8.5 μm in healthy individuals. This layer is composed of collagen fibrils and is clinically significant because it thickens in diseases such as asthma.

Lamina Propria

The subepithelial connective tissue (lamina propria) contains blood vessels (occupying ~2.8% of subepithelial tissue in health), lymphocytes, scattered inflammatory cells, smooth muscle, and submucosal glands composed of mucous and serous acinar cells that contribute to airway secretions.

Functional Significance

The bronchial mucosa serves as a critical barrier and immune interface. It provides mucociliary clearance (the "mucociliary escalator"), secretes protective mucus and antimicrobial substances, and actively participates in innate and adaptive immune responses through the release of cytokines, chemokines, and interferons. Epithelial cells also modulate underlying smooth muscle tone through the release of bronchoactive mediators.