What hormone primarily regulates the menstrual cycle?

The hormone that primarily regulates the menstrual cycle is estrogen. Estrogen is essential for the development and regulation of the female reproductive system and secondary sexual characteristics. During the menstrual cycle, estrogen levels rise and fall at specific times, facilitating various phases of the cycle.

In the follicular phase, estrogen is produced by developing ovarian follicles, which leads to the thickening of the endometrium in preparation for a potential pregnancy. A significant estrogen surge occurs just before ovulation, triggering the release of luteinizing hormone, which is crucial for the ovulation process. Following ovulation, estrogen works alongside progesterone to maintain the uterine lining.

While progesterone also plays a critical role during the luteal phase of the menstrual cycle in preparing the endometrium for implantation, it is ultimately estrogen that initiates and regulates the cycle overall. Understanding the interplay of these hormones is vital in grasping how menstrual cycles function, with estrogen emerging as the primary regulator.