Normal human endometrium. An ultrastructural survey.

An ultrastructural review of the cyclic changes of endometrial surface and glandular epithelial cells, stromal cells and the stromal microvasculature is presented. Endometrial biopsies were collected from infertile patients with endometriosis or tubal dysfunction. During the proliferative phase, the ergastoplasm and Golgi apparatus of surface and glandular epithelial cells become well-developed, while increasing numbers of mitochondria are seen. In the early secretory phase, the postovulatory triad composed of glycogen accumulation, nuclear channel system and giant mitochondria is described and its functional significance is discussed. Premenstrual cellular involution due to enhanced lysosomal activity such as apoptosis and lysosomal wrapping is detailed. Before ovulation, the endometrial stromal cells are primarily involved in the secretion and remodelling of the extracellular connective tissue fibers and ground substance. After predecidual change, the stromal cells exhibit marked macropinocytotic and phagocytotic properties. We suggest that these proteolytic activities of the stromal cells, together with the presence of blood-derived phagocytes, may account for endometrial clearance, since there are no lymphatic channels in the superficial endometrium. According to this hypothesis, tissue fluid may be drained via the fenestrated (venous) endometrial blood capillaries.