Now, as estrogen increases, that causes the initiation of the thickening of the endometrium. And so as estrogen increases, the endometrium begins to thicken as a result. So the developing follicle begins to release estrogen, which stimulates the thickening and formation of the endometrium in preparation for the implantation. And this is what is described by the cycle. So GnRH released by the Hypothalamus stimulates FSH and LH to also release and that causes estrogen to increase in concentration as a result. Now eventually what happens is Ovulation.