Ultrastructural Changes in Human Endometrium at Different Phases of the Menstrual Cycle and Their Functional Significance

Abstract

A review of the ultrastructure of normal human endometrium at different phases of the cycle is presented. The structural changes are correlated to the functional implications in the light of the recent knowledge on the functioning of cell organelles. Relatively undifferentiated cells of the beginning of the menstrual phase become functionally matured, proliferate and later degenerate. The appearance of the nucleolar channel system during the secretory phase coincides with the rise of progesterone level and facilitates the nucleocytoplasmic exchange. The secretion of the endometrial glands consists of glycogen, glycoproteins, lipids and mucopolysaccharides. Large autophagic vacuoles (giant lysosomes) digest various cell components at the end of the cycle. All the lamina functionalis of the endometrium is not shed, a part of it is regressed by focal death (autophagic vacuoles) and by total death (apoptosis) of individual cells.

The Nucleolar Channel System of Human Endometrium Is Related to Endoplasmic Reticulum and R-Rings

“…Similarly, in endometrial biopsies, lead phosphate precipitates in the cytoplasmic ER, the nuclear envelope, and, importantly, the NCS ( Figure 2C). Note the specificity of the labeling of only the ER but not mitochondria (mito), which are surrounded by a single layer of ER, a hallmark of the epithelial cells of this stage of the cycle (Verma, 1983). The presence of lead phosphate precipitates, and therefore glucose-6-phosphatase, in the lumen of the NCS cisternae identifies this organelle as ER derived ( Figure 2D).…”

The autophagosomal–lysosomal compartment in programmed cell death

“…7,8,11,25 Autophagic cell death also has been reported to occur in adulthood of insects and vertebrates including humans; it is often associated with the elimination of (large secretory) cells during adjustment of sexual organs and ancillary tissues to seasonal reproduction. 7,8,11,26,28,31 As to pathophysiology, autophagic cell death has been associated with experimental and human neurological diseases 32 ± 35 as well as cytotoxic drug treatment. 38 In summary, without attempting to force the data, the morphological observations strongly support the concept that autophagic cell death is characterised by features different from apoptosis ( Figure 1) and which is a phenomenon of general importance occurring in a broad spectrum of (patho)physiological conditions.…”

“…Thus, both types of cell death can occur simultaneously in tissues, 7,11,27 ± 29,35,38 but also subsequently as governed by the developmental programme. 31 Moreover, dying cells may share apoptotic and autophagic features (`mixed type'). 7,11,20,21,37,38,40 ± 44 The determinants for the eventual manifestation of either type of programmed cell death are poorly understood.…”

Characteristics of the uterine luminal surface epithelium at preovulatory and preimplantation stages in the marmoset monkey

“…At this stage, the relatively undifferentiated uterine epithelial cells proliferated and appeared to develop luminal cell organelles required for later phases. The large amount of euchromatin contained within uterine luminal epithelium during the proliferative phase suggested that gene transcription activity was occurring (Armstrong et al, 1973;Verma, 1983;Cornillie et al, 1985).…”

“…These large, complex structures have not been described previously in the uterine luminal epithelium of primates. Bearing some resemblance to OCBs, lysosome-like structures, given a variety of names such as "phagolysosomes," "autophagosomes," and "granulated bodies" have been identified in the primate glandular epithelium (Armstrong et al, 1973;Verma, 1983;Smith et al, 1987;Kaiserman-Abramof, 1989;Rune et al, 1992). The OCBs described here differed from these lysosome-like structures in abundance and size.…”