because your uterus lining is disintegrating. the lining of your uterus and blood capillaries present in your uterus to accommodate a baby in case of fertilization is now detaching from your uterus and falling as your period.
Girls
Menstruation
The muscles of the uterus called the myometrium are cramping from the constant movement to shed the uterus' lining.
No, girls don't need to have menstruated to get pregnant. Ovulation occurs BEFORE menstruation so you can get pregnant before menstruation.
Mensturation has nothing to do with virginity.
It is 12.
Well, the menstruation starts at the age of 12-13 in girls. The term for onset of menstruation is menarche .
Oh God, is this normal. Am i dying?
Because only women have the required body parts.
There are some rare cases where girls never have menstruation at 19 years due to a illness.
Yes, monthly menstruation effects hormone levels which can slightly affect a girls mood.
Boys don't have babies, girls do. A period is the lining of the uterus after it is no longer needed when a girl doesn't get pregnant.