The menstrual cycle is the scientific term for the physiological changes that can occur in fertile women for the purposes of sexual reproduction and fertilization. This article focuses on the human menstrual cycle, a "monthly" cycle that takes approximately 28 days to complete.
The menstrual cycle, under the control of the endocrine system, is necessary for reproduction. It is commonly divided into three phases: the follicular phase, ovulation, and the luteal phase. It is also occasionally misclassified using the uterine cycle: menstruation, proliferative phase, and secretory phase. Menstrual cycles are counted from the first day of menstrual bleeding. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction.
Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood (menses) slow then stop, and the lining of the uterus thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two become dominant (non-dominant follicles atrophy and die). Approximately mid-cycle, 24–36 hours after the Luteinizing Hormone (LH) surges, the dominant follicle releases an ovum, or egg in an event called ovulation. After ovulation, the egg only lives for 24 hours or less without fertilization while the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining and egg in a process termed menstruation.
In the menstrual cycle, changes occur in the female reproductive system as well as other systems (which lead to breast tenderness or mood changes, for example). A woman's first menstruation is termed menarche, and occurs typically around age 12-13. The average age of menarche is about 12.5 years in the United States, 12.72 in Canada, 12.9 in the UK and 13.06 ± 0.10 years in Iceland. The end of a woman's reproductive phase is called the menopause, which commonly occurs somewhere between the ages of 45 and 55.
Other articles related to "menstrual cycle, menstrual, cycle, cycles":
... / Stop up th’ access and passage to remorse,” Lady Macbeth asks for her menstrual cycle to stop ... By having her menstrual cycle stop, Lady Macbeth hopes to stop any feelings of sensitivity and caring that is associated with females ... La Belle furthers her argument by connecting the stopping of the menstrual cycle with the persistent infanticide motifs in the play ...
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... as the start of pregnancy the first day of the woman's last normal menstrual period, and the resulting fetal age is called the gestational age the date of conception (about two weeks ... As measured on a reference group of women with a menstrual cycle of exactly 28-days prior to pregnancy, and who had spontaneous onset of labor, the ... woman is a primipara or a multipara, respectively), the mother's race, parental age, length of menstrual cycle, and menstrual regularity), but these ...
... that artificial light at night does influence the menstrual cycle in humans and the estrus cycle in mice (cycles are more regular in the absence of artificial light at night) ... It has also been suggested that bright light exposure in the morning promotes more regular cycles ... has suggested that sensitivity of women's cycles to nightlighting is caused by nutritional deficiencies of certain vitamins and minerals ...
... or proliferative, phase of the thirteenth day of the menstrual cycle, the cumulus oophorus layer of the preovulatory follicle will develop an opening, or stigma, and ... The fully developed oocyte (gamete) is now at the behest of the menstrual cycle ... in their entirety by their respective articles, and placed into perspective by the menstrual cycle article ...
Famous quotes containing the words cycle and/or menstrual:
“Oh, life is a glorious cycle of song,
A medley of extemporanea;
And love is a thing that can never go wrong;
And I am Marie of Roumania.”
—Dorothy Parker (18931967)
“Virginity is now a mere preamble or waiting room to be got out of as soon as possible; it is without significance. Old age is similarly a waiting room, where you go after lifes over and wait for cancer or a stroke. The years before and after the menstrual years are vestigial: the only meaningful condition left to women is that of fruitfulness.”
—Ursula K. Le Guin (b. 1929)