Respiratory part of nasal mucosa

The respiratory part of nasal mucosa (Respiratory mucosa; Schneiderian membrane) lines the majority of the nasal cavity and is the principal functional lining of the respiratory portion of the nose. It is a pseudostratified ciliated columnar epithelium interspersed with goblet cells, resting on a basement membrane and a lamina propria rich in seromucinous glands, blood vessels, and immune cells.

Histological Composition

The respiratory nasal mucosa is composed of several key cell types:

• Ciliated columnar cells the most abundant cell type, each bearing approximately 50-200 motile cilia on its apical surface. These cilia beat in a coordinated metachronal wave pattern to propel the overlying mucus blanket toward the nasopharynx (mucociliary clearance).

• Goblet cells unicellular mucous glands scattered among the columnar cells that secrete mucin, contributing to the gel layer of the mucus blanket.

• Basal cells small, pyramidal progenitor cells that rest on the basement membrane and serve as stem cells for epithelial renewal and repair.

• Club cells (Clara-like cells) non-ciliated secretory cells that contribute to the periciliary sol layer and produce protective proteins.

Lamina Propria

Beneath the epithelium lies a highly vascular lamina propria containing:

• Seromucinous glands (Bowman-type mixed glands) that produce the majority of the nasal secretions, including lysozyme, lactoferrin, and secretory IgA.

• A rich vascular plexus including capacitance vessels (venous sinusoids), particularly prominent over the inferior and middle turbinates. These sinusoids can rapidly engorge or shrink, regulating airflow resistance and contributing to the nasal cycle.

• Immune cells including mast cells, lymphocytes, macrophages, and dendritic cells, forming part of the nasal-associated lymphoid tissue (NALT).

Functional Roles

The respiratory mucosa serves three primary physiological functions:

• Air conditioning warming and humidifying inspired air via the extensive subepithelial vascular network and glandular secretions. Inspired air is brought to near body temperature (37 °C) and close to 100% relative humidity before reaching the lower airways.

• Mucociliary clearance trapping inhaled particulate matter, pathogens, and allergens in the mucus blanket and transporting them posteriorly toward the nasopharynx at a rate of approximately 610 mm/min for swallowing or expectoration.

• Innate and adaptive immune defense through secretory IgA, antimicrobial peptides (defensins, lysozyme, lactoferrin), and resident immune cells that provide a first line of defense against inhaled pathogens.

Mucus Blanket

The mucus blanket overlying the respiratory epithelium has a biphasic structure:

• A deeper sol (periciliary) layer of low viscosity in which the cilia beat freely.

• A superficial gel layer of higher viscosity that traps particles and is propelled by the tips of the cilia during their effective stroke.

Clinical Relevance

Dysfunction of the respiratory nasal mucosa underlies numerous clinical conditions, including allergic rhinitis (goblet cell hyperplasia and eosinophilic infiltration), chronic rhinosinusitis (epithelial remodeling and impaired mucociliary clearance), and primary ciliary dyskinesia (congenital ciliary motility defects leading to recurrent sinonasal and pulmonary infections). The mucosa is also the primary target of topical intranasal corticosteroids and the site of entry for many respiratory viruses