Airway Mucosa

Overview – Airway Mucosa

The airway mucosa is a specialised lining of the respiratory tract that protects the lungs by filtering, humidifying, and clearing inhaled particles. Through mechanisms such as the mucociliary escalator and alveolar macrophages, the mucosa forms a critical barrier against pathogens and environmental debris. A clear understanding of airway mucosa is essential for interpreting respiratory physiology and pathologies like chronic bronchitis, asthma, and infections.

Clearance of Inhaled Particles

  • Cilia in the nasopharynx:
    • Beat backwards towards the pharynx
    • Particles are swallowed
Inhaled particles swallowed
cilia mucous dust particles
  • Mucociliary escalator:
    • Ciliated epithelium lines the conducting zone
    • Goblet cells and submucosal glands produce mucus to trap particles
    • Cilia beat upwards towards pharynx → swallowed or coughed out
    • Ciliary beat cycle: power stroke + recovery stroke
    • Mucus transport rate ≈ 1–2 mm/min
    • Airway surface liquid layer (sol layer) critical for ciliary function
Airway mucosa - respiratory epithelium
Blausen.com staff (2014). “Medical gallery of Blausen Medical 2014”. WikiJournal of Medicine 1 (2). via Wikimedia Commons
  • Alveolar macrophages:
    • Phagocytose particles and pathogens in alveoli
    • Release destructive enzymes to degrade foreign material
    • Dead macrophages may release enzymes → tissue damage
    • Debris cleared via:
      • Lymphatics
      • Mucociliary escalator
Airway mucosa - Alveolar macrophages
Delmalani18, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Mucosal Histology

Oropharynx & Laryngopharynx

  • Lined with protective epithelium (mainly stratified squamous, suited for food passage).
airway mucosa - pharynx histology
Courtesy of Prof. Hunter, Unit of Oral Pathology, University of Sheffield

Trachea

  • Mucosa:
    • Ciliated pseudostratified epithelium
    • Goblet cells (mucus secretion)
    • Lamina propria (dense elastic fibres, high elasticity)
  • Submucosa: seromucous glands
  • Adventitia: connective tissue, C-shaped cartilage rings, trachealis muscle (constricts trachea during coughing)
  • Clinical note: trachea at highest risk of infection; many pathogens grow best at 33–35 °C
airway mucosa - trachea
PBrieux, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Bronchi

  • Mucosa:
    • Ciliated pseudostratified → ciliated columnar epithelium (in lower bronchi)
    • Goblet cells produce mucus
    • Progressive reduction in cilia
  • Submucosa: seromucous glands
  • Adventitia: irregular cartilage rings → cartilage plates; increasing smooth muscle content
bronchi - mucosa
Creative Commons: https://guides.hostos.cuny.edu/bio140/7-29

Bronchioles

  • Sparsely ciliated simple cuboidal epithelium
  • No goblet cells
  • No submucosal mucous glands
  • No cartilage support (maintained by elastic fibres providing radial traction)
  • Increased smooth muscle proportion
Bronchioles
Source: Unattributable

Summary – Airway Mucosa

The airway mucosa provides a defence system that filters, humidifies, and clears inhaled particles. Through the mucociliary escalator and alveolar macrophages, it protects the alveoli from debris and infection. Histological changes along the trachea, bronchi, and bronchioles adapt the airway to differing functional demands. For a broader context, see our Respiratory Overview page.

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