Every menstruating woman develops an ovarian cyst every cycle. This is called a follicle cyst and it contains an egg. The ovary is directed by the pituitary gland in the brain. The ovary responds to FSH by maturing an egg. While doing this, the ovary makes the hormone estrogen.
Estrogen stimulates the lining of the uterus to grow.
The ovary matures the egg in a small cyst that eventually grows to be about 2cm in diameter. LH causes the cyst to break and release the egg. This is called ovulation. The remnant of the follicle cyst is called the corpus luteum and begins to produce the other ovarian hormone, progesterone. Progesterone converts the lining of the uterus to accept the pregnancy.