Which hormone is primarily responsible for the development of the female reproductive system during the menstrual cycle?

Estrogen plays a crucial role in the development and regulation of the female reproductive system during the menstrual cycle. This hormone is primarily responsible for promoting the growth and maintenance of the female reproductive organs, including the ovaries, uterus, and breasts.

During the menstrual cycle, estrogen levels fluctuate and follow a specific pattern, particularly rising during the follicular phase. This increase in estrogen leads to the thickening of the endometrial lining in preparation for potential implantation of a fertilized egg. Additionally, estrogen is involved in the regulation of other hormones that influence ovulation and menstrual cycling.

In contrast, while progesterone—which is also important in the menstrual cycle—primarily enhances the endometrial lining for possible pregnancy and maintains it after fertilization, it does not lead to the initial development of the female reproductive structures. Testosterone is more associated with male characteristics, and cortisol is a glucocorticoid that plays a role in stress response but is not directly involved in the menstrual cycle's reproductive processes.