Neuroendocrine Cross-Talk and Axial Regulation of Embryonic Implantation: Impact of Climate Change

Endometrium And Menstrual Cycle

The endometrium is made up of two layers viz, functionalis and basalis layers, both of these layers undergoes a sequence of changes during each ovulatory cycle that makes it momentarily capable to implantation. The functionalis layer makes the upper two thirds of the endometrium in which proliferation, secretion, and degradation occurs, however the basalis layer encompasses the lower one third and acts as site for the regeneration and renewal of tissues. In the proliferative phase during which the ovarian follicles grow and produces estrogen in higher quantity, which helps in the regeneration of the functionalis layer and hence the new growth of glands, stroma, and endothelial cells occurs. Next process is ciliogenesis during which the cells becomes ciliated present around the opening of glands, estradiol also helps in this process and starts on Day 7 or 8 of an ideal 28-day menstrual cycle (Ludwig and Spornitz et al., 1991). During the preovulatory17b-estradiol increases which leads to more proliferation and differentiation of epithelial cells of uterus (Norwitz et al., 2001). When ovulation occurs, the corpus luteum gets formed and secretion of progesterone starts. The progesterone acts on the endometrium which in turn increases the secretion of glycoproteins and peptides into the endometrial cavity in actively promotive fashion. Endometrial epithelial tissue proliferation ceases during this phase, because progesterone-helps in the blockade of receptor expression of estrogen and stimulation of 17b-hydroxysteroid dehydrogenase and sulfotransferase actions, which helps in the conversion of potent estradiol into estrone and then excreted out (Gurpide et al. 1976, Falany and Falany, 1996). About 7 days following the secretion of luteinizing hormone (LH) surge occurs, the secretory activity reaches upto the peak, the stroma of endometrial becomes tremendously edematous, and proliferation of blood vessels occurs in response to the sex steroids and secretion of prostaglandins (local factors).