Not to be confused with "mensuration", a forestry term meaning measurement.
Menstrual cycle
Menstruation is the shedding of the uterine lining (endometrium). It occurs on a regular basis in reproductive-age females of certain mammal species. Overt menstruation (where there is bleeding from the uterus through the vagina) is found primarily in humans and close evolutionary relatives such as chimpanzees.[1] The females of other placental mammal species have estrous cycles, in which the endometrium is reabsorbed by the animal (covert menstruation) at the end of its reproductive cycle. Many zoologists regard this as different from a "true" menstrual cycle.
Contents">Contents[hide]During pregnancy and for some time after childbirth, menstruation is normally suspended; this state is known as amenorrhoea, i.e. absence of the menstrual cycle. If menstruation has not resumed, fertility is low during lactation. The average length of postpartum amenorrhoea is longer when certain breastfeeding practices are followed; this may be done intentionally as Birth Control (lactational amenorrhea method).
EvolutionAll female placental mammals have a uterine lining that builds up when the animal is fertile, but is dismantled (menstruated) when the animal is infertile. Some anthropologists have questioned the energy cost of rebuilding the endometrium every fertility cycle. However, anthropologist Beverly Strassmann has proposed that the energy savings of not having tocontinuously maintain the uterine lining more than offsets energy cost of having to rebuild the lining in the next fertility cycle, even in species such as humans where much of the lining is lost through bleeding (overt menstruation) rather than reabsorbed (covert menstruation).[1][4] However, even in humans, much of it is re-absorbed.Many have questioned the evolution of overt menstruation in humans and related species, speculating on what advantage there could be to losing blood associated with dismantling the endometrium rather than absorbing it, as most mammals do.
Beginning in 1971, some research suggested that menstrual cycles of co-habiting human females became synchronized. A few anthropologists hypothesized that in hunter-gatherer societies, males would go on hunting journeys whilst the females of the tribe were menstruating, speculating that the females would not have been as receptive to sexual relations while menstruating.[5][6] However, there is currently significant dispute as to whether menstrual synchrony exists.[7]
Humans do, in fact, reabsorb about two-thirds of the endometrium each cycle. Strassmann asserts that overt menstruation occurs not because it is beneficial in itself. Rather, the fetal development of these species requires a more developed endometrium, one which is too thick to completely reabsorb. Strassman correlates species that have overt menstruation to those that have a large uterus relative to the adult female body size.[1]
Culture and menstruationMain article: Culture and menstruationCommon usage refers to menstruation and menses as a period, a contraction of "menstrual period". A woman might say that her "period is late," or simply "I'm late," when an expected menstrual period has not started. Delay or cessation of menstruation is commonly expected to be the first indication to a woman that she may be pregnant. However, this cannot be taken as certainty. Irregular cycles are common in the first few years of menstruation. Regularity of the menstrual cycle may be also be affected by physical or emotional stress. Moreover, continued menstruation in early pregnancy is not uncommon.[8]
Many religions have menstruation-related traditions. These may be bans on certain actions during menstruation (such as intercourse in orthodox Judaism, Hinduism and Islam), or rituals to be performed at the end of each menses (such as the mikvah in Judaism and the ghusl in Islam). Some traditional societies sequester females in residences, "menstrual huts", that are reserved for that exclusive purpose until the end of their menstrual period.
Since the late 1960s, some women have chosen to control the frequency of menstruation with long-acting hormonal birth control. This allows women to plan months in advance when she will menstruate as combined hormone pills are taken in 28 day cycles, 21 hormonal pills with either a 7 day break from pills, or 7 placebo pills during which the woman menstruates. Injections such as depo-provera became available in the 1960s, progestogen implants such as Norplant in the 1980s and extended cycle combined oral contraceptive pills in the early 2000s.
CharacteristicsPhysical_experience">Physical experienceSee also: Premenstrual SyndromeIn many women, various intense sensations brought about by the involved hormones and by cramping of the uterus can precede or accompany menstruation. Stronger sensations may include significant menstrual pain (dysmenorrhea), abdominal pain, migraine headaches, depression, emotional sensitivity, feeling bloated, changes in sex drive and nausea. Breastswelling and discomfort caused by premenstrual water retention or hormone fluctuation is very common. Binge eating occurs in a minority of menstruating women.[9] This may be due to fluctuation in beta-endorphin levels. More severe symptoms may be classified as premenstrual dysphoric disorder (PMDD). The sensations experienced vary from woman to woman and from cycle to cycle.
Emotional_reactions">Emotional reactionsWomen may experience emotional disturbances associated with menstruation. These range from the irritability popularly associated with premenstrual syndrome (PMS), to tiredness, or "weepiness" (i.e. tears of emotional closeness). A similar range of emotional effects and mood swings is associated with pregnancy.[10] Rarely, in individuals susceptible to psychotic episodes, menstruation may be a trigger (menstrual psychosis). Flow">FlowThe normal menstrual flow follows a "crescendo-decrescendo" pattern; that is, it starts at a moderate level, increases somewhat, and then slowly tapers. Sudden heavy flows or amounts in excess of 80 mL (hypermenorrhea or menorrhagia) may stem from hormonal disturbance, uterine abnormalities, including uterine leiomyoma or cancer, and other causes. Doctors call the opposite phenomenon, of bleeding very little, hypomenorrhea. Duration">DurationThe typical woman bleeds for two to seven days at the beginning of each menstrual cycle.[2][11] Prolonged bleeding (metrorrhagia, also meno-metrorrhagia) no longer shows a clear interval pattern. Dysfunctional uterine bleeding is hormonally caused bleeding abnormalities. Dysfunctional uterine bleeding typically occurs in premenopausal women who do not ovulate normally (i.e. are anovulatory). All these bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant patients may bleed, a pregnancy test forms part of the evaluation of abnormal bleeding. Menstrual productsMain article: Menstrual productMost women use something to absorb or catch their menses. There are a number of different methods available.
Disposable items:
Reusable items:
In addition to products to contain the menstrual flow, pharmaceutical companies likewise provide products - commonly non-steroidal anti-inflammatory drugs (NSAIDs) - to relieve menstrual cramps. Some herbs, such as dong quai, raspberry leaf and crampbark, are also claimed to relieve menstrual pain;[12] however there is no documented scientific evidence to prove this.[citation needed]
Further readingHuman physiology and Endocrinology of Sexual reproduction[show] v • d • e
Menstrual cycle
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