Menstruation and the Menstrual Cycle

by Women's Health Information Center

What is menstruation?

Menstruation is a woman's monthly bleeding. It is also called menses, menstrual period, or period. When a woman has her period, she is menstruating. The menstrual blood is partly blood and partly tissue from the inside of the uterus (womb). It 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 helps a woman's body prepare for the possibility of pregnancy each month. A cycle starts on the first day of a period. The average menstrual cycle is 28 days long. However, a cycle can range anywhere from 23 days to 35 days.

The parts of the body involved in the menstrual cycle include the brain, pituitary gland, uterus and cervix, ovaries, fallopian tubes, and vagina. Body chemicals called hormones rise and fall during the month and make the menstrual cycle happen. The ovaries make two important female hormones, estrogen and progesterone. Other hormones involved in the menstrual cycle include follicle-stimulating hormone (FSH) and luteinizing hormone (LH), made by the pituitary gland.

What happens during the menstrual cycle?

In the first half of the menstrual cycle, levels of estrogen rise and make the lining of the uterus grow and thicken. In response to follicle-stimulating hormone, an egg (ovum) in one of the ovaries starts to mature. At about day 14 of a typical 28-day cycle, in response to a surge of luteinizing hormone, the egg leaves the ovary. This is called ovulation.

In the second half of the menstrual cycle, the egg begins to travel through the fallopian tube to the uterus. Progesterone levels rise and help prepare the uterine lining for pregnancy. If the egg becomes fertilized by a sperm cell and attaches itself to the uterine wall, the woman becomes pregnant. If the egg is not fertilized, it either dissolves or is absorbed into the body. If pregnancy does not occur, estrogen and progesterone levels drop, and the thickened lining of the uterus is shed during the menstrual period.

In the illustration below, an egg has left an ovary after ovulation and is on its way through a fallopian tube to the uterus.

What is a typical menstrual period like?

During the menstrual period, the thickened uterine lining and extra blood are shed through the vaginal canal. A woman's period may not be the same every month, and it may not be the same as other women's periods. Periods can be light, moderate, or heavy, and the length of the period also varies. While most menstrual periods last from three to five days, anywhere from two to seven days is considered normal. For the first few years after menstruation begins, periods may be very irregular. They may also become irregular in women approaching menopause. Sometimes birth control pills are prescribed to help with irregular periods or other problems with the menstrual cycle.

Sanitary pads or tampons, which are made of cotton or another absorbent material, are worn to absorb the blood flow. Sanitary pads are placed inside the panties; tampons are inserted into the vagina.

What kinds of problems do women have with their periods?

Women can have various kinds of problems with their periods, including pain, heavy bleeding, and skipped periods.

Amenorrhea - the lack of a menstrual period. This term is used to describe the absence of a period in young women who haven't started menstruating by age 16, or the absence of a period in women who used to have a regular period. Causes of amenorrhea include pregnancy, breastfeeding, and extreme weight loss caused by serious illness, eating disorders, excessive exercising, or stress. Hormonal problems (involving the pituitary, thyroid, ovary, or adrenal glands) or problems with the reproductive organs may be involved.

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