The Ultrastructural Development of Air-Blood Barrier in Human Fetal Lung

Kim, Bum Soo; Lim, In Seok; Kim, Kyung Yong; Lee, Won Bok

Abstract

The air-blood barrier represents the maturity of developing lung. The development of air-blood barrier in human fetal lung was studied by transmission electron microscopy. The results obtained were as follows. 1. The formation of air-blood barrier started at 16 week of postcoitum, which was the end of pseudoglandular period. The basement membranes began to be fused with each other as the capillaries penetrated between epithelial cells of primitive alveoli. 2. The flattening of the type II alveolar cells was observed only around the site of fused basement membranes, which seemed to be developed not by mechanical force but by induction of the fused basement membrane. 3. The basement membranes of capillaries and alveoli were relatively flat until the fusion occurred, but they showed severe folds with the occurrence of fusion. But with the proceeding of the terminal sac period, the folds greatly decreased. In summary, the air-blood barrier began to develop at the end of pseudoglandular period and was formed as capillaries penetrated the cytoplasms of epithelial cells devoided of the nuclei. The fused basement membranes seems to play an important role in the development of air-blood barrier.