During the follicular stage of the menstrual cycle, both FSH and estrogen are high, but aren't estrogen and FSH on a negative feedback loop?
Is it just because FSH is not directly involved in the increase of estrogen (it is the follicle that increases estrogen) that both of them remain high?
Since this is not my area of expertise, I searched Google under the key words "FSH estrogen relationship" to get this:
http://www.google.com/search?client=safari&rls=en&q=FSH+estrogen+relationship&ie=UTF-8&oe=UTF-8
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
Yes, you are correct that follicle-stimulating hormone (FSH) and estrogen are on a negative feedback loop. Normally, FSH stimulates the development of a follicle in the ovaries, which then produces estrogen. As estrogen levels rise, it exerts a negative feedback effect on the pituitary gland, reducing the secretion of FSH.
However, during the follicular stage of the menstrual cycle, FSH and estrogen both remain high because of a specific mechanism in the body. At the beginning of the menstrual cycle, the level of FSH rises, stimulating the growth and development of multiple follicles in the ovaries. As the follicles grow, they start producing increasing amounts of estrogen.
In response to increasing levels of estrogen, the pituitary gland receives a signal to decrease the secretion of FSH. This reduction in FSH prevents multiple follicles from continuing to grow and promotes the dominance of a single, mature follicle. However, this feedback mechanism takes some time to fully take effect.
So, in the early stages of the follicular phase, both FSH and estrogen can remain high. FSH stimulates the growth of multiple follicles, leading to an increase in estrogen production by these developing follicles. As the cycle progresses, the dominant follicle releases more estrogen, which eventually leads to a decrease in FSH levels and the selection of a single mature follicle for ovulation.
Overall, it is because FSH is not directly involved in the increase of estrogen, and there is a time lag in the negative feedback loop, that both FSH and estrogen can be high during the early stages of the follicular phase of the menstrual cycle.