Endometrial shedding and regeneration: an electron microscopic study in the human being

Whether the stroma of the endometrium, the spongy layer or the deeper parts of the endometrial glands is the origin of the postmenstrual surface epithelium is a matter of different opinions. The endometrium was examined during the second day of the menstrual bleeding in 20 fertile females using the scanning electron microscope (SEM). Proliferative and secretory endometrium were present denoting the onset of regeneration by that time. The superficial parts of the endometrial glands in some areas were projecting on the surface of the remaining spongy layer like worms having nipple like heads and an opening like a mouth. Endometrial regeneration began in the deeper parts of the endometrial glands as columns of rounded cells with central cavities which had everted thick edges on reaching the surface. These everted edges were growing in all directions to cover the remaining spongy layer with surface epithelium containing ciliated and non-ciliated cells. Exposure of the deeper parts of the glands is essential for regeneration. The delay in shedding the superficial parts of the glands may play an important role in dysfunctional uterine bleeding.