The main function of any hormone is to carry chemical messages from one tissue or organ to another tissue or organ in the body. The sex hormones produced by the ovaries allow the reproductive cycle to function in a proper manner.
During the reproductive years, ovaries produce oestrogen and progesterone. These two are the major female sex hormones and are controlled by the pituitary gland in the brain. This gland produces a follicle-stimulating hormone (FSH) which goes via the bloodstream to the ovaries and causes the follicles (that contain the eggs) in the ovaries to mature and to produce oestrogen.
At the time of ovulation, a luteinising hormone (LH) is secreted by the ovaries and also by the pituitary gland when oestrogen reaches a certain level. The most advanced follicle of one of the ovaries releases an egg which enters the Fallopian tube and is available for fertilisation. The follicle changes by becoming a yellow cyst (corpus luteum), which starts producing progesterone as well as oestrogen.
Oestrogen and progesterone
Oestrogen and progesterone play an important part in building up the endometrium (lining of the uterus), which is prepared every month for a possible pregnancy. If the egg is not fertilised, hormone production declines. When the progesterone drops below a certain level, the endometrium sheds over a few days and this is called menstruation.
As the oestrogen and progesterone levels drop, the production of FSH is set in motion again and the whole cycle starts over. When women grow older, the eggs in their ovaries diminish, there are fewer follicles available and hormone levels begin to fluctuate. When this begins to happen, it is usually the start of menopause.
The main female sex hormone is oestrogen. It is made in the ovarian tissue from a number of precursor hormones and plays many roles, including helping your body through the important processes of ovulation, conception and pregnancy, as well as helping to regulate cholesterol and maintaining bone density.
Once menopause has occurred, the oestrogen production from the ovaries declines to about one third of its previous level. Precursor hormones from the ovaries are still circulated through the bloodstream and reach the fat cells where they are converted into oestrogens. This explains why obese women with plenty of fat cells have higher levels of circulating oestrogen after menopause, compared to skinny women.
Osteoporosis and a number of other disorders can be associated with this drop in oestrogen production, which can be alleviated by oestrogen replacement.
Progesterone works with oestrogen to help regulate the menstrual cycle and prepare your body for conception and pregnancy. Oestrogen and progesterone work as a team to prepare the uterus for the coming embryo: oestrogen causes proliferation of the endometrium (“building the house”), and progesterone changes the proliferated endometrium into a secretory phase (“putting the furniture in”).
With the onset of menopause the body’s progesterone levels drop. During the reproductive years, progesterone formed part of the hormonal control of regular menstruation, and its decline in the perimenopause is one of the reasons why your periods may become irregular.
If you opt for hormone therapy in your menopause and your uterus is still intact, your doctor will probably prescribe a drug that contains both oestrogen and progesterone, as oestrogen-only therapy will increase your risk of developing endometrial cancer.
Not only men produce androgens (small amounts of testosterone) – these are also produced in precursor form in the ovaries and adrenal glands. These hormones are partially responsible for the spurt of growth girls experience in early puberty.
During menopause, your androgen production drops by almost 50%. Using androgens as part of hormone therapy could make you feel more energetic, increase your libido and help relieve hot flushes, but androgens also have significant side effects and the doctor will prescribe them only if there is a specific indication.
Reviewed and updated by Dr Alan Alperstein, obestetrician and gynaecologists in Cape Town, in February 2011.
Previously partly reviewed by Dr Mike Davey, President of the South African Menopause Society & Dr Tobie de Villiers, gynaecologist and committee member of both the South African Menopause and International Menopause Societies.