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.
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.