Periods:
When, Who, Why, What ?
When?Puberty begins between 8 and 13. About 2 to 2½ years after a girl's breasts begin to develop she usually gets her first menstrual period. Your first period doesn't happen until all the parts of your reproductive system have matured and are working together.
Why?On average women lose 1 to 3 ounces of fluid over 3-7 days of menstruation. Periods are essential to having a child. A period is the leftover wall of the uterus that is shed if the egg is not fertilized. A period is made of blood, tissue, and the unfertilized egg.
More Info
http://kidshealth.org/teen/sexual_health/girls/menstruation.html#
http://www.bbc.com/earth/story/20150420-why-do-women-have-periods |
Who?All women get periods, some earlier or later then others. Even though all human females go through the menstrual cycle most animals do not menstruate. Of the animals that do menstruate, chimps and gibbons having easily detectable cycles.
What?About once a month, a tiny egg leaves one of the ovaries — a process called ovulation — and travels down one of the fallopian tubes toward the uterus. In the days before ovulation, the hormone estrogen stimulates the uterus to build up its lining with extra blood and tissue, making the walls of the uterus thick and cushioned. This happens to prepare the uterus for pregnancy: If the egg is fertilized by a sperm cell, it travels to the uterus and attaches to the cushiony wall of the uterus, where it slowly develops into a baby.
If the egg isn't fertilized, though — which is the case during most of a woman's monthly cycles — it doesn't attach to the wall of the uterus. When this happens, the uterus sheds the extra tissue lining. The blood, tissue, and unfertilized egg leave the uterus, going through the vagina on the way out of the body. This is a menstrual period. Your first period is called a menarche. |