Why do girls have their periods?

Answer 1

A woman's period comes at the end of her menstrual cycle. The average length of a woman's menstrual cycle is 28 days (one month, which is why a woman's period is sometimes called "her monthlies"), but the cycle can be as short as 22 days or so, and as long as 35 days or so.

About a week or two into the cycle, one of her ovaries releases an egg into her uterus (see the Related Link below for a diagram). The ovaries are two almond-shaped egg sacs, on either side of the uterus (where the baby grows and is birthed from), and are connected to the uterus by tubes called fallopian tubes. Every month, one of the ovaries releases an egg into the uterus. This is called "ovulation." The walls of the uterus then develop a sort of protective layer of blood and tissue, to cushion the egg.

If, by the end of the month, the egg has not been fertilized by a man's sperm, the woman's body will dispose of the egg and the protective tissue that cushions it. This is what's known as a period. The blood, tissue, and egg are flushed out of the woman's body, and come out of her vagina.

When the period is over -- when the egg and all the tissue and blood have been flushed out -- the cycle begins again.

If a sperm cell does, in fact, fertilize the egg, then a baby will begin to grow and develop in the uterus (also known as the womb). Once a woman becomes pregnant, she will cease to have a monthly period until after the baby is born.

Answer 2

The menstrual period, this is the time that the woman's uterus sheds the endometrial layer of the uterus that wasn't needed (since no ovum was fertilized and no embryo was implanted in it) and prepares for a new one the following month. During the menstrual cycle, the uterus prepares for the implantation of a "baby" by developing a thick, richly vascular (lots of blood vessels) endometrium or lining of the uterus. If it is not used, the endometrium is sloughed off (shed) (menstruation or bleeding) and the process starts again.

Girls have periods to get rid of the uterus lining that is developed in case of fertilisation of the egg