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Menstrual Cycle


The expulsion of tissue and blood from the uterus lasts from three to eight days, with much variation among women. Some women experience painful cramps during menstruation, which are the result of uterine contractions that expel the endometrium. Hormones known as prostaglandins are produced by uterine cells during menstruation, and the excessive production of prostaglandins is associated with stronger uterine contractions and more intense cramps. Menstrual cramps can be treated by drugs that inhibit the production of prostaglandins in uterine cells. Aspirin, ibuprofin, and naproxin sodium are all effective anti-prostaglandin drugs. It is important to take these medications at the onset of the menstrual flow, otherwise prostaglandin production can proceed for several hours unchecked, and the drugs will not be effective in reducing pain.

Some women also experience premenstrual syndrome (PMS), a condition occurring some time in the secretory phase prior to menstruation. Symptoms of PMS include mood changes, water retention and bloating, increase in appetite and cravings, cramps, breast pain, and headaches. Researchers are not sure what causes PMS, but the sharp drop in progesterone that occurs at about day 22 may be involved in triggering these physical and emotional symptoms. While no cure for PMS exists, experts recommend that women who experience PMS reduce their salt intake, engage in more exercise, and maintain a healthy diet during this time. The B vitamins may also be effective in reducing PMS symptoms. Some women have found relief in taking the medications prescribed for menstrual cramps, while lowering caffeine intake can be useful in reducing premenstrual breast pain.

Girls begin menstruating at the onset of puberty, at about the age of 12 or 13, although the onset of menstruation may be earlier or later, depending on the amount of body fat. The first menstrual period is called the menarche; during the first few cycles, ovulation may be absent.

Menopause is the cessation of the menstrual cycle, when ovulation and menstruation cease. The cessation of menstruation is gradual and is preceded by menstrual cycles in which ovulation does not occur. The menstrual cycle becomes irregular before finally stopping completely. The onset of menopause is individually variable, occurring between the ages of 45 to the late fifties.



Ferin, Michel, et al. The Menstrual Cycle: Physiology, Reproductive Disorders, and Infertility. New York: Oxford University Press, 1993.

Sloane, Ethel. Biology of Women. 3rd ed. Albany, NY: Delmar, 1993.


Mestel, Rosie. "Are Periods a Protection Against Men?" New Scientist 140, no. 1893 (October 2, 1993): 8.

Quadagno, David, et al. "The Menstrual Cycle: Does It Affect Athletic Performance?" The Physician and Sportsmedicine 19, no. 3 (March 1991): 121.

Segal, Marion. "A Balanced Look at the Menstrual Cycle." FDA Consumer 27, no. 1 (December 1993): 32.

Kathleen Scogna



—The front portion, or neck, of the uterus.

Corpus luteum

—The site on the ovary from where the ovum was released; the corpus luteum then releases hormones to prepare the endometrium for implantation of the fertilized ovum.


—The blood-rich interior lining of the uterus.


—A female reproductive hormone secreted by the follicles.


—The structure in which eggs develop within the ovary.

Follicle-stimulating hormone (FSH)

—A hormone released by the pituitary gland that stimulates ovum production and maturation.

Graafian follicles

—Maturing ovarian follicles.

Human chorionic gonadotropin

—Hormone secreted by the embryo that maintains the corpus luteum.

Luteinizing hormone

—Hormone that acts with LH to stimulate the maturation of follicles.


—First menstrual period.


—Cessation of the menstrual cycle.


—Sloughing off the lining of the uterus.


—Female reproductive organ that contains the eggs.


—Process in which an egg is ejected from an ovarian follicle.


—Hormone secreted by the corpus luteum; maintains the endometrium.


—Complex fatty acids occurring in most human tissues.


—Organ in female mammals in which embryo and fetus grow to maturity.


—Passage from the uterus to outside the female body.

Additional topics

Science EncyclopediaScience & Philosophy: Mathematics to Methanal trimerMenstrual Cycle - Proliferative Phase, Secretory Phase, Menstruation