The morphological development of the pulmonary epithelium of human foetuses studied by light- and electron microscopy.

Abstract

The morphological development of pulmonary epithelium of 24 human foetal lungs was studied by light- and electron microscopy in embryos with a crown-rump length between 20 and 160 mm. The glandular and the canalicular period in the development of lungs were identified. In the beginning of the glandular period the epithelium was uniformly of tall columnar type. In the later glandular period the epithelium in most peripheral bronchial tubules diminished in thickness to cuboidal type. In larger bronchial tubules ciliated and non-ciliated cells could be distinguished. The cytoplasmic glycogen was abundant, and increasing in amount from 20 to 70 mm crown-rump length, decreasing during the later glandular period. Junctional complexes, desmosomes and a continuous basement membrane were present at 20 mm crown-rump length. In the canalicular stage the epithelial lining of developing alveoli consisted of two cell types identified as alveolar cells of type I and II. Lamellar bodies characteristics of type II cells were only occasionally observed.