A woman’s reproductive organs include the vagina, uterus, two fallopian tubes and two ovaries. The female reproductive cycle (menstrual cycle) is a highly coordinated process involving hormones produced by the hypothalamus and pituitary gland (in the brain) and by the ovaries.
Women are born with more than one million eggs, which are stored in the ovaries. These eggs will be depleted over the course of a woman’s reproductive life span. To mature an egg, a woman’s hypothalamus releases a hormone called gonadotropin-releasing hormone (GnRH). GnRH stimulates the release of two other hormones – follicle stimulating hormone (FSH) and luteinizing hormone (LH) – from the pituitary gland. These hormones, in turn, stimulate the woman’s ovary to produce a follicle. The follicle is a fluid-filled sac that contains an egg (oocyte). The follicle also produces estrogen, which helps to regulate the release of FSH and LH and stimulates the lining of the uterus (the endometrium) to thicken to prepare to receive an embryo.
A follicle matures and reaches a point where it is ready to release the egg at about day 14 of a woman’s ovulatory cycle. A surge of LH from the pituitary gland causes the follicle to release the egg in a process known as ovulation. When this occurs, the egg is released from the ovary and travels down one of the fallopian tubes. The egg is now in position to be fertilized by a man’s sperm following intercourse. The hormone progesterone is made by the ovary after ovulation to provide the proper environment for implantation and to support an early pregnancy. If an egg is fertilized, it must travel down the fallopian tube to the uterus where it will implant itself in the endometrium about six days later. If the egg is not fertilized, the uterus sheds the endometrium about two weeks later and a woman menstruates.