Scanning electron microscopic observations of the human respiratory tract.

As viewed by scanning electron microscopy, the luminal surface of the human trachea at 12 weeks' gestation shows a predominance of microvillous-covered, nonciliated cells, in contrast to the heavily ciliated tracheobronchial surface seen at 34 weeks' gestation. Hyaline membrane disease produces a confluent lining material in the lung periphery that obscures the bronchiolar and alveolar surface architecture. Large saucer-shaped alveoli, numerous alveolar pores, and an abundance of in situ alveolar macrophages are observed in chronic bronchitis and in emphysematous lungs; The scanning electron microscope offers an additional tool for the study of developmental and pathological processes in the human respiratory tract.