So theca cells use cholesterol to form androgens and then they release those androgens and give the androgens to granulosa cells. And the granalosa cells contain a special enzyme that is capable of transforming the androgens produced by FECA cells into estrogen. Now once they produce estrogen the estrogen basically does several things. 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.