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 saucershaped 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.
Greenwood MF, Holland P. Scanning Electron Microscopic Observations of the Human Respiratory Tract. Am J Dis Child. 1975;129(3):289-294. doi:10.1001/archpedi.1975.02120400007002