The menstrual cycle is a cycle of physiological
changes that can occur in fertile females. Overt menstruation (where
there is blood flow
from the uterus
through the vagina) occurs primarily in humans and
close evolutionary relatives such as chimpanzees.[1]
Females of other species of placental mammal undergo estrous
cycles, in which the endometrium
is completely reabsorbed by the animal (covert
menstruation) at the end of its reproductive
cycle. This article focuses on the human menstrual cycle.
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; although some sources use a different set of
phases: menstruation, proliferative phase, and
secretory phase.[2]
The length of each phase varies from woman to woman and cycle to
cycle, though the average menstrual cycle is 28 days.[3]
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, 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
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. The end of a woman's reproductive
phase is called the menopause, which commonly occurs
somewhere between the ages of 45 and 55.
Menstruation is also called menstrual bleeding,
menses, catamenia or a
period. The flow of menses normally serves as a
sign that a woman has not become pregnant. (However, this cannot be
taken as certainty, as a number of factors can cause bleeding during
pregnancy; some factors are specific to early pregnancy, and some can cause
heavy
flow.)[8][9][10]
During the reproductive years, failure to menstruate may provide
the first indication to a woman that she may have become
pregnant.
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).[11][12]
The average blood loss during menstruation is 35
milliliters with 10–80 ml considered normal.[13]
(Because of this blood loss, women are more susceptible to iron
deficiency than men are.)[14]
An enzyme called
plasmin inhibits
clotting in the menstrual
fluid.[15]
Painful cramping in the abdomen, back, or upper thighs is common
during the first few days of menstruation (most women experience
some pain during menstruation). Severe uterine pain during
menstruation is known as dysmenorrhea, and it is most common
among adolescents and younger women (affecting about 67.2% of
adolescent females).[16]
When menstruation begins, symptoms of premenstrual
syndrome (PMS) such as breast tenderness and irritability
generally decrease.[12]
Many sanitary
products are marketed to women for use during their
menstruation.
IN OTHER WORDS.... GIRL WITH MENSES GO SWIMMING POOL FOR
FUCK?
ei thanks for summarizing the wall of text
