Menstruation Totally Explained

Everything about Menstruation totally explained

See also "Mensuration", a term sometimes used to describe Measurement. 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's bleeding from the vagina) is found primarily in humans and close evolutionary relatives such as chimpanzees. The females of other species of placental mammal have estrous cycles, in which the endometrium is reabsorbed by the animal (covert menstruation) at the end of its reproductive cycle.

Overview

Eumenorrhea denotes normal, regular menstruation that lasts for a few days (usually 3 to 5 days, but anywhere from 2 to 7 days is considered normal). The average blood loss during menstruation is 35 millilitres with 10-80 mL considered normal; many females also notice shedding of the endometrium lining that appears as tissue mixed with the blood. An enzyme called plasmin — contained in the endometrium — tends to inhibit the blood from clotting. Because of this blood loss, women have higher dietary requirements for iron to prevent iron deficiency. Many women experience uterine cramps, also referred to as dysmenorrhea, during this time. A vast industry has grown to provide drugs to aid in these cramps, as well as sanitary products to help manage menses.

As part of the menstrual cycle

Menstruation is the most visible phase of the menstrual cycle. Menstrual cycles are counted from the first day of menstrual bleeding, because the onset of menstruation corresponds closely with the hormonal cycle.
During pregnancy and for some time after childbirth, menstruation doesn't normally take place — this state is known as amenorrhoea, for example absence of the menstrual cycle.

Evolution

All 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 posited that the energy savings of not having to continuously 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).
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 wouldn't have been as receptive to sexual relations while menstruating. However, there's currently significant dispute as to whether menstrual synchrony exists.
Humans do, in fact, reabsorb about two-thirds of the endometrium each cycle. Strassmann asserts that overt menstruation occurs not because it's 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.

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