Why does the lining of the uterus break?

I don't really feel like researching but..

The lining of the uterus breaking is a sign of menstration.. During the cycle, a woman's ovaries stick to the uteran walls waiting for a potential candidate (sperm) to fertalize it.. if the egg is not fertalized, our body no longer has use for the egg or the uteran wall, so our body sheds or "breaks" the wall, thus the period happens...it breaks because the body no longer needs that sticky wall holding the egg. and if the egg is fertalized then the wall will thicken (I think) in order to keep the egg stable for the development of the fetus.