A mature follicle is produced when rising levels of estrogen in the bloodstream causes the hypothalamus to produce luteinizing hormone (LH). This causes one of the follicles to burst and release an ovum for possible fertilization, the escape being known as ovulation. The remains of the follicle stay in the ovary, secreting estrogen and a second hormone, progesterone, which prepares the uterus liningmycontentbreak (endometrium) to receive and nourish a fertilized egg.