Editing Menstrual cycle (section)

{{Short description|Natural changes in the human female reproductive system}}
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{{About|biological aspects of the reproductive cycle in humans|information specific to monthly periods|menstruation|and|menstruation (mammal)}}
{{Use dmy dates|date=March 2021}}
[[File:Menstrual cycle.svg|thumb|upright=1.8|right|Menstrual cycle]]
The '''menstrual cycle''' is a series of natural changes in [[hormone]] production and the structures of the [[uterus]] and [[ovaries]] of the [[female reproductive system]] that makes [[pregnancy]] possible. The ovarian cycle controls the production and release of [[Egg cell|eggs]] and the cyclic release of [[estrogen]] and [[progesterone]]. The uterine cycle governs the preparation and maintenance of the lining of the uterus (womb) to receive an [[embryo]]. These cycles are concurrent and coordinated, normally last between 21 and 35 days, with a [[median]] length of 28 days. [[Menarche]] (the onset of the first period) usually occurs around the age of 12 years; menstrual cycles continue for about 30–45 years.

Naturally occurring hormones drive the cycles; the cyclical rise and fall of the [[follicle stimulating hormone]] prompts the production and growth of [[oocyte]]s (immature egg cells). The hormone estrogen stimulates the uterus lining ([[endometrium]]) to thicken to accommodate an embryo should [[Human fertilization|fertilization]] occur. The blood supply of the thickened lining provides [[nutrient]]s to a successfully [[Implantation (embryology)|implanted]] embryo. If implantation does not occur, the lining breaks down and blood is released. Triggered by falling progesterone levels, [[menstruation]] (commonly referred to as a "period") is the cyclical shedding of the lining, and is a sign that pregnancy has not occurred.

Each cycle occurs in phases based on events either in the ovary (ovarian cycle) or in the uterus (uterine cycle). The ovarian cycle consists of the [[follicular phase]], [[ovulation]], and the [[luteal phase]]; the uterine cycle consists of the menstrual, proliferative and secretory phases. Day one of the menstrual cycle is the first day of the period, which lasts for about five days. Around day fourteen, an egg is usually released from the ovary.

The menstrual cycle can cause some women to experience [[premenstrual syndrome]] with symptoms that may include  [[Breast tenderness|tender breasts]], and [[Fatigue|tiredness]]. More severe symptoms that affect daily living are classed as [[premenstrual dysphoric disorder]], and are experienced by 3–8% of women. During the first few days of menstruation some women experience [[Dysmenorrhea|period pain]] that can spread from the abdomen to the back and upper thighs. The menstrual cycle can be modified by [[hormonal birth control]].