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