
Menstruation
(Menstrual Cycle)
What is menstruation?
Menstruation is a woman's monthly bleeding, also called a period. When you
menstruate, your body is shedding the lining of the
uterus (womb). Menstrual
blood flows from the uterus through the small opening in the
cervix, and passes
out of the body through the vagina. Most menstrual periods last from three to
five days.
What is the menstrual cycle?
Menstruation is part of the menstrual cycle, which prepares your body for
pregnancy each month. A cycle is counted from the first day of one period to the
first day of the next period. The average menstrual cycle is 28 days long.
Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in
young teens.
Body chemicals called hormones rise and fall during the month to make the
menstrual cycle happen.
What happens during the menstrual cycle?
In the first half of the cycle, levels of estrogen (the "female hormone")
start to rise and make the lining of the uterus (womb) grow and thicken. At the
same time, an egg (ovum) in one of the ovaries starts to mature. At about day 14
of a typical 28-day cycle, the egg leaves the ovary. This is called ovulation.
After the egg has left the ovary it travels through the
Fallopian tube to the
uterus. Hormone levels rise and help prepare the uterine lining for pregnancy. A
woman is most likely to get pregnant during the three days before ovulation or
on the day of ovulation. Keep in mind, women with cycles that are shorter or
longer than average may ovulate earlier or later than day 14.
If the egg is fertilized by a man's
sperm cell and attaches to the uterine
wall, the woman becomes pregnant. If the egg is not fertilized, it will break
apart. If pregnancy does not occur, hormone levels drop, and the thickened
lining of the uterus is shed during the menstrual period.

Next: What is a typical menstrual period like? »
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