Estrogen plays a central and multifaceted role in the menstrual cycle. Here are the key points:

• Estrogen is mainly produced by ovarian follicles during the first half of the menstrual cycle (follicular phase). Its levels gradually rise as the follicles mature.
• Estrogen helps to thicken and repair the lining of the uterus (endometrium) after menstruation, preparing it for potential embryo implantation.
• It signals the pituitary gland to produce a surge in luteinizing hormone (LH), which triggers ovulation—the release of a mature egg from the ovary.
• Estrogen also thins cervical mucus, making it easier for sperm to travel to fertilize the egg.
• After ovulation, estrogen levels dip briefly but then rise again along with progesterone, produced by the corpus luteum, to maintain the uterine lining during the luteal phase.
• If fertilization does not occur, estrogen and other hormone levels fall, leading to menstruation as the uterine lining sheds.
• Beyond the menstrual cycle, estrogen supports secondary sex characteristics (like breast development), bone health, skin moisture, mood regulation, and heart health.

In summary, estrogen regulates the buildup and maintenance of the uterine lining, triggers ovulation, and facilitates fertility by preparing the reproductive tract for fertilization and potential pregnancy. Its fluctuating levels throughout the menstrual cycle coordinate these critical reproductive processes. This description covers estrogen's role thoroughly and highlights its critical functions within the menstrual cycle. If you want, I can also explain the roles of other hormones involved.