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[L. menstruare, to discharge the menses]
The cyclic, hormonally generated sloughing of the uterine endometrium, which occurs between puberty and menopause and is accompanied by bloody vaginal discharge. The onset of menstruation (menarche) usually occurs during puberty (9 to 17 years of age). When a woman's ovum is not fertilized, the corpus luteum undergoes involution, which causes progesterone levels to drop, which in turn triggers menses.
SYN: SEE: catamenia
SEE: ovary for illus; SEE: lactation amenorrhea method; SEE: menstrual cycle
menstrual (mĕn′stroo-ăl)
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, adj.
The average menstrual period displays the following characteristics: an intermenstrual interval that varies between 18 and 40 days, with an average of 27 to 30 days; and a menstrual flow that lasts between 3 and 7 days, 4 to 5 days average. Menstrual blood contains normal, hemolyzed, and sometimes agglutinated red blood cells; disintegrated endometrial and stromal cells; and glandular secretions. In general, menstrual blood does not coagulate, but passage of occasional clots is not unusual.

Blood loss varies widely among women; however, it usually is consistent from month to month in the same individual. Average monthly blood loss ranges from 44 to 80 mL but may be lessened by the use of oral contraceptives and increased by the presence of an intrauterine device. Menstrual blood loss is the most common single cause of female iron-deficiency anemia. Estimating a patient's blood loss from interviewing is difficult because many women are poor judges of the volume of their flow. A rough estimate of blood loss may be made by querying the number, type, and amount of saturation of tampons or sanitary pads used each day of the period. When noting the number of pads or tampons used daily, the historian should determine the reason for changes; some women may change for reasons other than pad saturation.

Indications of excessive or abnormal menstrual flow include a need to change saturated tampons or pads hourly; passage of clots, esp. when larger than 2 cm in diameter or occurring on other than the first full day of menses; and duration of flow exceeding 7 days in one or more cycles. Menstruation normally ceases during pregnancy, may or may not occur during lactation, and permanently ceases with menopause.
SEE: sanitary napkin; SEE: tampon, menstrual

Menstrual irregularities: Failure to menstruate may be caused by congenital abnormalities; physical disorders, e.g., obesity, malnutrition, or disease; excessive exercise; emotional and hormonal disturbances affecting the ovaries, pituitary, thyroid, or adrenal glands. An absence of flow when normally expected is called amenorrhea;scanty flow is known as oligomenorrhea; painful menstruation is dysmenorrhea. Excessive loss of blood is termed menorrhagia; loss of blood during intermenstrual periods is known as spotting or metrorrhagia.

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