Menstrual Cycle Overview
Menstruation, or having a period, occurs every month that an egg is not fertilized in a woman's reproductive system. A menstrual cycle lasts from the first day of one period to the first day of the next period. The average length of a menstrual cycle is 28 days, although a cycle can be as short as 21 days or as long as 35 days, according to the National Women's Health Information Center (NWHIC).
Pre-Menstruation
The ovaries, two small oval-shaped organs containing a woman's eggs, are located on either side of the uterus in the lower abdomen. A fallopian tube connects each ovary to the uterus, the muscular organ that contains a fetus during pregnancy. During the first half of the menstrual cycle, levels of the female hormone estrogen begin to rise in the body, spurring the uterus to produce a thick lining of blood and tissue to support an embryo, or fertilized egg, according to Kids Health. While the uterine lining is thickening, an egg is maturing in one of the ovaries. At the midpoint of the menstrual cycle, ovulation occurs and the egg travels from the ovary through the fallopian tube to the uterus.
Menstruation
Menstruation occurs if an egg remains unfertilized by a man's sperm. When an egg is not fertilized, hormone levels begin to drop, causing the uterus to shed the uterine lining. The remnants of the unfertilized egg and the blood and tissue that formed the uterine lining exit the body through the vagina. The menstrual period begins a few days after the hormone levels drop. Most periods last from three to five days, although periods that last from two to seven days are also normal, according to the NWHIC.
While menstruation usually occurs every month, a missed period can occur occasionally and does not have to be related to pregnancy. Periods may be skipped or delayed due to a variety of factors, including illness, stress, starting a hormonal birth-control method, too much exercise, weight gain or loss or poor nutrition.
Menstruation usually first occurs between the ages of 9 and 16 and continues until a woman reaches menopause between the ages of 45 to 55, according to Planned Parenthood. When a woman enters menopause, she stops producing eggs, no longer has a menstrual cycle and is unable to become pregnant.
Symptoms
In addition to normal blood flow from the vagina, women may experience heavy bleeding, pain and cramps in the abdominal area during a period. Cramps are caused by the uterine contractions that help the uterine lining separate from the uterus and leave the body, according to Planned Parenthood. Over-the-counter pain relievers can be helpful in easing cramps.
Some women experience the symptoms of premenstrual syndrome (PMS) one or two weeks before menstruation occurs, due to changing hormone levels. Symptoms of PMS may include depression, crying, tender breasts, increase in acne, fatigue, headaches, mood swings, difficulty sleeping, diarrhea, constipation, bloating, food cravings and achy joints or muscles. Most women experience at least one PMS symptom, according to Planned Parenthood.
