The onset of puberty in females triggers the shedding of unfertilised eggs and the LINING OF THE UTERUS. The lining of the uterus is shed each month if the mature egg is not fertilized. This process is called menstruation. The first menstrual period a young girl will have marks menarche.
Specialized hormones such as progesterone and estrogens play a vital role in the development and shedding of the lining of the uterus in each menstrual cycles.