Which hormone is primarily responsible for the changes during the menstrual cycle?

The primary hormone responsible for the changes during the menstrual cycle is estrogen. Throughout the menstrual cycle, estrogen plays a crucial role in regulating the growth and maturation of the ovarian follicles and preparing the uterine lining for potential implantation of a fertilized egg.

During the follicular phase of the menstrual cycle, rising levels of estrogen lead to the thickening of the endometrium, the lining of the uterus, making it more receptive to a fertilized ovum. This hormone also is involved in the feedback loop that triggers the surge of luteinizing hormone, which is essential for the ovulation process.

Estrogen levels fluctuate throughout the cycle, peaking just before ovulation and then decreasing if fertilization does not occur, followed by a rise again during the luteal phase. This cyclical rise and fall of estrogen is fundamental for the menstrual cycle's regularity and physiological changes.