The main function of any hormone is to carry chemical messages from one tissue or organ to another tissue or organ in the body. Regarding the sex hormones of the ovaries and their control by higher centres in the brain, this message system is responsible for the reproductive cycle to function in a proper manner.
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During the reproductive years, ovaries produce oestrogen and progesterone. These two are the major female sex hormones which 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 (containing the eggs) in the ovaries, to mature and to produce oestrogen.
At the time of ovulation, a luteinising hormone(LH) is secreted, 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 – this is called menstruation.
As the oestrogen and progesterone levels drop, the production of FSH is set into motion again, thereby starting the whole cycle over again. When women grow older, the eggs in their ovaries diminish, there are less follicles available and hormone levels begin to fluctuate. When this starts happening, it is usually the start of menopause.
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