Studies on the cytodynamics of human endometrial regeneration. II. Transmission electron microscopy and histochemistry.

The morphologic observations made in this study indicate that postmenstrual endometrial resurfacing occurs by proliferation of epithelial cells originating from the stumps of residual basal glands and uterine surface lining, bordering the denuded areas, respectively. Endometrial stromal cells or glands of the residual spongiosa are not involved in uterine surface repair. The mechanism whereby the new surface develops, it is proposed, is by endomitotic division. This contention is supported by the accelerated nuclear DNA and intracytoplasmic RNA synthesis, and absence of mitosis in the newly formed surface epithelial cells. The results indicate, furthermore, that uterine surface reconstruction, which is completed by cycle day 5, is independent of ovarian hormonal stimuli, whereas further endometrial growth, connective tissue remodeling, and metabolic enzyme synthesis are influenced by the gradual increase of preovulatory estrogens.