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Why do women have periods?

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Quick Answer

Menstrual periods allow the female body to discharge excess uterine tissue and eggs when fertilization doesn't occur, according to KidsHealth. In preparation for ovulation, the hormone estrogen causes the uterine lining to thicken with extra tissue and blood, creating a cushioned surface for a fertilized egg to attach to. Instead of attaching, an unfertilized egg passes out of the body through the vagina, and the unneeded tissue is shed.

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Why do women have periods?
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Full Answer

The menstrual cycle is the number of days between a menstrual period, and it prepares the body for a potential pregnancy by stimulating changes in estrogen levels. It occurs monthly and lasts an average of 28 days with a menstruation period of 3 to 5 days, according to the U.S. Office on Women's Health. Menstruation is characterized by periodic blood flow that passes from the uterus to the cervix before exiting the vagina.

The cramps associated with menstruation are caused by muscle contractions in the uterus, while premenstrual syndrome, or PMS, is caused by hormonal fluctuations, KidsHealth states. Menstruation begins in childhood when a girl's reproductive organs mature during puberty. Two oval-shaped sacs, known as ovaries, store and produce thousands of ova, or eggs. During ovulation, at least one egg leaves one of the ovaries and passes through a fallopian tube leading to the uterus. If a sperm cell is deposited inside the female body, the sperm has a chance of fertilizing the egg before it exits the uterus.

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