The Female reproductive system consists of the uterus (womb), a muscular pear-shaped expandable organ about 3in/7.5cm long and 2in/5cm wide, two ovaries (connected to the uterus by the Fallopian tubes), and the cervix, which joins the lower end of the uterus to the top end of the vagina.

The system is activated by hormones in the bloodstream. These are produced by the pituitary, a tiny gland at the base of the brain. Their output is controlled by a different part of the brain, the hypothalamus. During a woman's menstrual cycle the ovaries produce the sex hormones estrogen and progesterone in varying amounts, and small amounts of testosterone and other male hormones. These hormones do not work in isolation: estrogen, for example, works with testosterone to give a woman her sex drive. Estrogen and progesterone are responsible for the regulation of the menstrual cycle during a woman's reproductive life, her female characteristics, and her sex drive and fertility. If she becomes pregnant, these hormones enable the womb to support the growing baby by making the endometrium (lining of the womb) thick and rich with tiny blood vessels.

Hormones enable the ovaries to release an egg each month for possible fertilization. If sperm are present, the egg is fertilized in the Fallopian tube and passes down into the uterus, where it attaches itself to the endometrium and grows. If the egg is not fertilized. the levels of estrogen and progesterone fall, the endometrium shrinks because there are no hormones to support it, and the uterus expels this and the unfertilized egg as a menstrual period. The whole cycle then starts up all over again.

Most women have around 400 menstrual periods throughout their lives. Although the level of hormones fluctuates throughout each cycle, it is essential that the balance is correct, for even the smallest imbalance can cause menstrual disorders, or even infertility. Many problems associated with the menopause are due to the diminishing levels of hormones.