Airways

Overview

• Conducting Airways
  • “conducting zone” includes:
    • nose
    • nasopharynx
    • larynx
    • trachea
      • contains a cartilaginous layer composed of C-shaped hyaline cartilages
        • prevent collapse of tracheal lumen, especially during expiration
    • bronchi
      • contain a cartilaginous layer composed of discontinuous cartilage plates
      • distal most extent of mucous producing goblet cells 
    • bronchioles
    • terminal bronchioles
  • bring air into and out of lungs
  • warm, humidify, and filter air
  • anatomic dead space
    • do not participate in gas exchange
  • walls contain smooth muscle
    • sympathetic and parasympathetic innervation regulates airway diameter
      • mechanism for altering airway resistance and airflow
• Respiratory Airways
  • “respiratory zone” includes:
    • respiratory bronchioles 
      • lined by simple cuboidal cells
    • alveolar ducts
    • alveolar sacs 
      • alveolar wall lined by type I and type II pneumocytes 
        • type II pneumocytes proliferate after alveolar damage and secrete surfactant 
  • participate in gas exchange
    • structures are lined with alveoli
    • exchange of oxygen and carbon dioxide between alveoli and pulmonary capillary blood occurs rapidly and efficiently across alveoli
      • alveolar walls are thin and have large surface area for diffusion
      • blood-gas barrier = alveolar type I cell – interstitium – capillary endothelial cell