[Electron microscopic observations of alveoli development and epithelial differentiation in the fetal lung of the Chinese].

OBJECTIVE

To observe the development of the alveoli and the differentiation of the epithelium in the fetal lung of Chinese.

METHODS

Chinese human lung tissues were obtained from 20 fetuses of 10 to 34 weeks old, and the ultrastructural changes of the alveolar epithelial cells were observed using both optical and transmission electron microscope.

RESULTS

At the first 10 to 16 weeks of development, the lung showed a tubular structure, the epithelial cells were columnar and poorly differentiated. At weeks 17 to 24, the bronchioles increased and the epithelial cells were differentiated to approach maturity. A few lamellar bodies were observed in the cuboidal lining cells with the majority being type II alveolar cells at 25 weeks, when the primitive alveolar was formed. In this stage many primitive epithelial cells could be seen, which appeared primordial in form before evolving into type II and type I cells and perhaps served as epithelial stem cells or progenitor cells. From about 26 weeks, type I cells were observed but most of the epithelial cells were type II cells. Type I cells began to increase in the alveolar epithelium until 32 weeks.

CONCLUSIONS

The alveolar type II cells and type I cells are probably both derived from the same precursor cells or stem cells, and no evidence has shown that type II cells may differentiate into type I cells during the development of the fetal lung.