[Submicroscopic changes in the glandular epithelium of the endometrium in cows during the estrous cycle].

During the sexual cycle the structural changes in the cells of the glandular epithelium in the endometrium of a cow are more pronounced than those in the luminal epithelium. Microvilli appear on cell surface during pro-oestrus; in later stages the microvilli disappear and the apical parts penetrate into the lumen. The relative volume of mitochondria increases from pro-oestrus to culminate in oestrus and metoestrus and to drop in dioestrus. The values of the volume and surface area of granular endoplasmic reticulum are also at their highest level in oestrus and metoestrus. The lowest volume and surface area of smooth membranes are recorded in dioestrus, then it markedly increases to culminate in metoestrus. The incidence of lysosomes is variable and their volume culminates in metoestrus. The proliferation of the glandular epithelium has the highest intensity in oestrus and reaches its peak values in metoestrus when the apical parts of cytoplasm contain the largest amounts of smooth-walled vesicles and vacuoles, partly also secretory granules, and when the signs of secretion are observed.