Morphology of the distal conducting airways in rhesus monkey lungs.

This study systematically characterizes the organization and nature of epithelial populations in the distal airways of the adult rhesus monkey. Infusion-fixed lungs were evaluated using airway dissection and scanning and transmission electron microscopy. We found that a true bronchiole free of cartilage and alveolar outpockets was not consistently present. Cartilage and alveolar outpocketings were often observed within the same airway generation. The epithelial population of nonalveolarized terminal conducting airways was pseudostratified columnar, consisting of ciliated, mucous, and basal cells. The respiratory bronchiole found immediately distal to the terminal conducting airways had two clearly demarcated zones of distinctly different epithelial populations. Overlying the pulmonary artery was the same pseudostratified ciliated columnar epithelial population observed in nonalveolarized terminal airways. The epithelial population in the remainder of the respiratory bronchiole, not associated with the pulmonary artery, was simple nonciliated cuboidal with a few squamous cells. The cuboidal nonciliated bronchiolar cell differs from the mucous cell by having few small granules and rough and smooth endoplasmic reticulum. The extension of the ciliated, mucous, and basal cells several generations into the respiratory bronchiole in rhesus monkey has not been observed in rodents and other laboratory mammals. Data from studies of human airways, although not explicit, suggest that the rhesus monkey epithelial cell pattern resembles the pattern in the human terminal airways.