Studies on the cytodynamics of human endometrial regeneration. I. Scanning electron microscopy.

Stereoscopic morphologic studies on regenerating cyclic endometrium indicate that endometrial repair lasts 48 hours, beginning between cycle Days 2 to 3 and ending between cycle Days 4 to 5. During this period, endometrial repair is focused on the neoformation of surface epithelium and is initiated only when and where the zona basalis is denuded from the overlying secretory spongiosa. The surface epithelium is derived from a simultaneous proliferation of dual origin: first from the exposed ends of basal glands and second from the persistent and intact surface lining of cornual and isthmic regions, bordering the denuded areas. The lack of estrogen-dependent morphologic alterations (mitosis and ciliogenesis) in the uterine mucosa during the regenerative period suggests that the initial factors and cellular processes operating in endometrial reconstruction are purely a reflection of tissue repair and are independent of cyclic hormonal stimuli.