Menstruation << `mehn` stru AY shuhn >> is the loss of blood and cells that occurs about once a month in most women of childbearing age. During each month, blood and cells build up in the lining of a woman’s uterus (womb), a hollow, pear-shaped organ that holds a baby during pregnancy. The thickening of the lining prepares the uterus for pregnancy. If pregnancy does not occur, the lining breaks down. The blood and cells are discharged through the vagina, which is a canal that leads from the uterus to the outside of the body. The process of menstruation lasts from three to seven days, and this period of time is called the menstrual period, or the menses.
Most girls experience their first menstrual period between the ages of 10 and 16. A woman stops having menstrual periods during a time of life called menopause, which occurs between the ages of 45 and 55 in most women.
The menstrual cycle.
Menstruation is part of the menstrual cycle, the process that prepares a woman for pregnancy. This cycle repeats itself every 24 to 32 days during the reproductive years of most women. Several hormones regulate the phases of the menstrual cycle.
During menstruation, some eggs (female sex cells) begin to mature in the ovaries, two organs located near the uterus. As the eggs develop, the surrounding cells release estradiol (one of the estrogen hormones) into the bloodstream. As the estrogen level increases, menstrual bleeding stops and the lining of the uterus thickens in preparation for receiving a fertilized egg. The increase in estrogen also causes the pituitary gland to release a hormone that travels to the ovaries and causes the most mature egg to be released. The release of the egg, called ovulation, occurs about 14 days before the next menstrual period. The egg travels to the uterus through the fallopian tube. After ovulation, the ovary that has just released the egg produces another hormone, progesterone, which prepares the uterine wall so that implantation (attachment) of the fertilized egg may occur (see Progesterone).
Fertilization occurs if the egg unites with a male sex cell called a sperm in the fallopian tube. The fertilized egg attaches to the uterine wall and continues its nine-month development into a baby (see Reproduction, Human). The placenta, an organ that supplies food and oxygen to the baby, secretes hormones that prevent menstruation during pregnancy. If the egg is not fertilized, there is no placenta to secrete hormones. Thus, the uterine lining breaks down and is shed about 14 days after ovulation.
Effects of menstruation.
Some women have mild to moderate abdominal cramps a few days before or during menstruation. This discomfort, called dysmenorrhea, results from contractions of the uterus and is usually normal. During the days before menstruation begins, some women experience emotional or physical symptoms that may include depression, anxiety, fatigue, headache, body swelling, or pain in the breasts. This condition is called premenstrual syndrome (PMS).
Menstruation signifies good health if it occurs regularly and without excessive pain, fatigue, or blood loss. Most women carry on their usual activities. Menstrual discharge can be absorbed either by a sanitary napkin, a disposable pad that covers the vaginal opening, or by a tampon, a roll of absorbent material worn inside the vagina.
The most common reason for a young woman to miss a menstrual period is pregnancy. Other reasons include emotional stress, weight loss, and abnormal hormonal balance. If a woman frequently misses her period or if it occurs less often than every 35 days, she should consult a doctor.
