Which hormone is primarily responsible for regulating the female reproductive cycle?

The hormone primarily responsible for regulating the female reproductive cycle is estrogen. Estrogen plays a critical role in the development and regulation of the female reproductive system and secondary sexual characteristics. Throughout the menstrual cycle, estrogen levels fluctuate and are pivotal in promoting the maturation of follicles in the ovaries, stimulating the thickening of the endometrial lining, and triggering ovulation.

During the first half of the menstrual cycle, estrogen levels rise, leading to an increase in the thickness of the uterine lining, preparing it for potential implantation of an embryo. Additionally, estrogen has a feedback effect on the hypothalamus and pituitary gland, affecting the secretion of other hormones that are part of the reproductive cycle.

While luteinizing hormone and follicle-stimulating hormone are also important in regulating aspects of the reproductive cycle, such as stimulating ovulation and follicle development, estrogen's central role in orchestrating the overall cycle makes it the primary hormone for regulation. Therefore, its significant influence on the female reproductive system underscores why the answer is estrogen.