FSH: FSH is released into the blood from the pituitary gland. It is triggered by a fall in progesterone at the end of the previous cycle. It acts upon the ovary, causing development of a follicle (eggs to mature) in the ovary. The maturing follicles release oestrogen. Oestrogen: Oestrogen is released into the blood by the follicles in the ovaries. It causes repair and proliferation (growth/thickening) of the uterus lining (endometrium). It also inhibits the release of FSH so that only one egg matures during one cycle.LH: As more oestrogen is released, it stimulates a surge of LH to be released from the pituitary gland. This causes ovulation (the release of an egg from the ovarian follicle/ovary)