Firstly, it initiates the thickening of the lining of the uterus. It basically thickens the endometrium in preparation for a potential implantation by a zygote if fertilization actually takes place. And what estrogen also does is it goes up to the hypothalamus and via a positive feedback loop it stimulates more GnRH to actually be released. And because we have more going onotrop and releasing hormone in the blood system we have more LH and FSH because this positively stimulates the interior pituitary gland. Now, the estrogen also actually directly affects the interior pituitary gland and as a result it releases more LH and FSH into our blood. So we see that more estrogen means more LH and FSH.