The ovarian cycle is a series of events in

the ovaries that occur during and after the

maturation of the oocyte (egg or ovum).

During their reproductive years,

nonpregnant females usually experience a

cyclical sequence of changes in their ovaries

and uterus. Each cycle takes about one

month and involves both oogenesis, the

process of formation and development of

oocyte, and preparation of the uterus to

receive a fertilized ovum. Hormones secreted

by the hypothalamus, anterior pituitary

gland, and ovaries control the principal

events.

The uterine (menstrual) cycle is a

concurrent series of changes in the

endometrium of the uterus to prepare it for

the arrival of a fertilized ovum that will

develop in the uterus until birth. If

fertilization does not occur, the lining

(stratum functionalis) of the endometrium is

shed during menstruation.

Name of phase Days

menstrual phase 1–4

follicular phase (also known as proliferative phase)

5–13

ovulation (not a phase, but an event dividing phases)

14

luteal phase (also known as secretory phase)

15–26

ischemic phase (some sources group this with secretory phase)

27–28

Menstruation is also called menstrual bleeding, menses, a period or catamenia. The flow of menses normally serves as a sign that a woman has

not become pregnant.A woman's first menstruation is termed menarche, and is one of the later

stages of puberty in girls. The average age of menarche in humans is 12 years, but is normal anywhere between ages 8 and 16. Factors such as

heredity, diet and overall health can accelerate or delay menarche

The cessation of menstrual cycles at the end of a woman's reproductive life is termed menopause. The average age of

menopause in women is 51 years, 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).[6] The average blood loss during menstruation is 35 millitres with 10–80 ml

considered normal;[7] many women 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 than do males to prevent iron deficiency. Many women experience uterine cramps during this time (severe cramps or other symptoms are called dysmenorrhea).

Through the influence of a rise in follicle stimulating hormone (FSH), five to seven tertiary-stage ovarian follicles are recruited for entry into the next menstrual cycle.

These follicles, that have been growing for the better part of a year in a process known as folliculogenesis, compete with each other for dominance. Under the influence of several hormones, all but one of these follicles will undergo atresia, while one (or occasionally two) dominant follicles will continue to maturity. As they mature, the follicles secrete increasing amounts of estradiol , an estrogen.

The estrogens that follicles secrete, initiate the formation of a new layer of endometrium in the uterus, histologically identified as the proliferative endometrium.

During the follicular phase the lining of the uterus thickens, stimulated by gradually increasing amounts of estrogen.

Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two follicles become dominant (non-dominant follicles atrophy and die). The dominant follicle releases an ovum or egg in an event called ovulation.

. (An egg that is fertilized by a spermatozoon will become a zygote, taking one to two weeks to travel down the fallopian tubes to the uterus. If the egg is not fertilized within about a day of ovulation, it will die and be absorbed by the woman's body.[5])When the egg has matured, it secretes enough estradiol to trigger the acute release of luteinizing hormone (LH).In the average cycle this LH surge starts around cycle day 12 and may last 48 hours. The release of LH matures the egg and weakens the wall of the follicle in the ovary.

• The egg is swept into the fallopian tube by the fimbria - a fringe of tissue at the end of each fallopian tube. If fertilization occurs, it will happen in the fallopian tube.

• In some women, ovulation features a characteristic pain called mittelschmerz

• The sudden change in hormones at the time of ovulation also causes light mid-cycle bleeding for some women. An unfertilized egg will eventually disintegrate or dissolve.

The corpus luteum is the solid body formed in the ovaries after the egg has been released into the fallopian tube which continues to grow and divide for a while.After ovulation, the residual follicle transforms into the corpus luteum under the support of the pituitary hormones. This corpus luteum will produce progesterone in addition to estrogens for approximately the next 2 weeks. Progesterone plays a vital role in converting the proliferative endometrium into a secretory lining receptive for implantation and supportive of the early pregnancy.

It raises the body temperature by one-half to one degree Fahrenheit

If fertilization of an egg has occurred, it will travel as an early blastocyst through the fallopian tube to the uterine cavity and implant itself 6 to 12 days after ovulationOne very early signal consists of human chorionic gonadotropin (hCG), a hormone that pregnancy tests can measure. This signal has an important role in maintaining the corpus luteum and enabling it to continue to produce progesterone.In the absence of a pregnancy and without hCG, the corpus luteum demises and inhibin and progesterone levels fall. This will set the stage for the next cycle. Progesterone withdrawal leads to menstrual shedding (progesterone withdrawal bleeding), and falling inhibin levels allow FSH levels to rise to raise a new crop of follicles.

Two sex hormones play a role in the control of the menstrual cycle: estrogen and progesterone:Estradiol peaks twice, during follicular growth and during the luteal phase. Progesterone remains virtually absent prior to ovulation, but becomes critical in the luteal phase and during pregnancy. Many tests for ovulation check for the presence of progesterone. After ovulation the corpus luteum — which develops from the burst follicle and remains in the ovary — secretes both estradiol and progesterone. Only if pregnancy occurs do hormones appear in order to suspend the menstrual cycle, while production of estradiol and progesterone continues. Abnormal hormonal regulation leads to disturbance in the menstrual cycle

These sex hormones come under the influence of the pituitary gland, and both FSH and LH play necessary roles:FSH stimulates immature follicles in the ovaries to grow. LH triggers ovulation. The gonadotropin-releasing hormone of the hypothalamus controls the pituitary, yet both the pituitary and the hypothalamus receive feedback from the follicle.

Unlike almost all other species, the external physical changes of a human female near ovulation

are very subtle. In contrast, other species often signal receptivity through heat, swellings, and/or changes in color in the genital area. Humans are

the only mammal to lack obvious, visible manifestations of ovulation, although some argue

that the extended estrus period of the bonobo (reproductive-age females are in heat for 75% of

their menstrual cycle)[14] has a similar effect to the lack of a "heat" in human females.[15] While women

can be taught to recognize their own ovulation (fertility awareness), whether men can detect

ovulation in women is highly debated. At least one recent study has argued that men are more likely

to initiate sex with fertile women[16], while another has found male-initiated sex to occur at a constant

rate throughout the menstrual cycle.[17]

Evidence suggests that eggs are formed from germ cells early in fetal life. The number is reduced to an estimated 400,000 to 450,000 immature ova

residing in each ovary at puberty. The menstrual cycle, as a biologic event, allows for ovulation of

one egg typically each month. Thus over her reproductive lifetime a woman will ovulate

approximately 400 to 450 times. All the other eggs dissolve by a process called atresia. As a woman's

total egg supply is formed in fetal life,[18] to be ovulated decades later, it has been suggested that

this long lifetime may make the chromatin of eggs more vulnerable to division problems, breakage,

and mutation than the chromatin of sperm, which are produced continuously during a man's

reproductive life.

High ovarian volume and high antral follicle countsUltrasound image of an ovary at the beginning of a menstrual cycle. No medications are being given.The ovary is outlined in blue. There are numerous antral follicles visible - marked with red spots16 are seen in this image, this ovary had a total of 35 antrals (only 1 plane is shown above)This is a polycystic ovary, with a higher than average antral count and volume (ovary = 37 by 19.5mm)This woman had very irregular periods and was a "high responder" to injectable FSH medication

Normal ovarian volume and "normal" antral follicle counts

Ultrasound image of an ovary at the beginning of a menstrual cycle. No medications are being given.The ovary is outlined in blue. 9 antral follicles are seen - marked with red spotsThe ovary has normal volume (cursors measuring ovary = 30 by 17.8mm)This woman had regular periods and a normal response to injectable FSH drugs

Low ovarian volume and low antral follicle counts

The left ovary is outlined in blue and is small (low volume)Only 1 antral follicle is seenThis woman had regular periods and a normal day 3 FSH test

The right ovary from the same womanThis ovary is also small with only 2 antral folliclesShe only had 3 antrals total - from both ovariesAttempts to stimulate her ovaries for IVF were not successfu

Apparently normal menstrual flow can occur without ovulation preceding it.In some women, follicular development may start but not be completed; nevertheless, estrogens will form and will stimulate the uterine lining.Anovulatory flow resulting from a very thick endometrium caused by prolonged, continued high estrogen levels is called estrogen breakthrough bleeding.Anovulatory bleeding triggered by a sudden drop in estrogen levels is called estrogen withdrawal bleeding.[19]Anovulatory flow commonly occurs prior to menopause (premenopause) or in women with polycystic ovary syndrome

Sudden heavy flows or amounts in excess of 80 ml (hypermenorrhea or menorrhagia) are not normal.Very little flow (less than 10ml) is called hypomenorrheaProlonged flow (metrorrhagia, also meno-metrorrhagia) no longer shows a clear interval pattern. Dysfunctional uterine bleeding refers to hormonally caused flow abnormalities, typically anovulation.All 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 abnormalAmenorrhea refers to a prolonged absence of menses during the reproductive years of a woman. For example, women with very low body fat, such as athletes, may cease to menstruate. Amenorrhea also occurs during pregancy.

The condition precocious puberty has caused menstruation to occur in girls as young as eight months old.[20]

is any collection of fluid, surrounded by a very thin wall, within an ovary. Any

ovarian follicle that is larger than about two centimeters is

termed an ovarian cyst. An ovarian cyst can be as small

as a pea, or as large as a grapefruit.

Ovarian cancer cell

is a malignant tumor, of any histology, on or within an ovary.

(abbreviated PCOS or PCO), also known clinically as Stein-Leventhal syndrome, is an endocrine disorder that affects approximately one in ten women.[1] It occurs amongst all races and nationalities, is the

most common hormonal disorder among women of reproductive age, and is a leading cause of infertility.[citation needed] The principal

features are weight problems, lack of regular ovulation and/or menstruation, and excessive amounts or effects of androgenic

(masculinizing) hormones

Laparoscopic oophorectomy

In the case of humans, oophorectomies are most often performed due to diseases such as ovarian cysts or cancer; prophylactially to

reduce the chances of developing ovarian cancer or breast cancer; or in conjunction with removal of the uterus.

•In medicine and (clinical) genetics preimplantation genetic diagnosis (PGD) (or also known as Embryo Screening) refers to procedures that are performed on embryos prior to implantation, sometimes even on oocytes prior to fertilization. PGD is considered an alternative to prenatal diagnosis. Its main advantage is that it avoids selective pregnancy termination as the method makes it highly likely that the baby will be free of the disease under consideration.

PGD thus is an adjunct to assisted reproductive technology, and requires

in vitro fertilization (IVF) to obtain oocytes or embryos for evaluation. The term preimplantation genetic

screening (PGS) is used to denote procedures that do not look for a specific disease but use PGD

techniques to identify embryos at risk. PGD is a poorly chosen phrase because, in medicine, to

"diagnose" means to identify an illness or determine its cause. An oocyte or early-stage

embryo has no symptoms of disease. They are not ill. Rather, they may have a genetic condition that

could lead to disease. To "screen" means to test for anatomical, physiological, or genetic conditions in

the absence of symptoms of disease. So, both PGD and PGS should, be referred to as types of embryo

screening.

(IVF) is a technique in which egg cells are fertilised by sperm outside the woman's womb

The most fertile period (the time with the highest likelihood of pregnancy resulting

from sexual intercourse) covers the time from some 5 days before ovulation until 1–2 days after ovulation. In an average 28 day cycle

with a 14-day luteal phase, this corresponds to the second and the beginning of the third week of the cycle. Fertility awareness methods

of birth control attempt to determine the precise time of ovulation in order to find the

relatively fertile and the relatively infertile days in the cycle.

If a woman wants to conceive, the most fertile time occurs between 19 and 10 days prior to the expected menses. Many women use ovulation detection kits that detect the

presence of the LH surge in the urine to indicate the most fertile time. Other ovulation detection systems rely on

observation of one or more of the three primary fertility signs (

basal body temperature, cervical fluid, and cervical position).

Among women living closely together, the onsets of menstruation may tend to synchronise

somewhat. This McClintock effect was first described in 1971, and possibly explained by the

action of pheromones in 1998.[11] However, subsequent research has called this conclusion

into question.[12]

Estrogens and progesterone-like hormones make up the main active ingredients of hormonal birth control methods such as the pill. Typically they cause regular monthly flow that roughly mimics a menstrual cycle in appearance, but suppresses ovulation. With most pills, a woman takes hormone pills for 21 days, followed by 7 days of non-functional placebo pills or no pills at all, then the cycle starts again.

During the 7 placebo days, a withdrawal bleeding occurs; this differs from ordinary menstruation, and skipping the placebos

and continuing with the next batch of hormone pills maysuppress it. (There are two main versions of the pill:

monophasic and triphasic. With triphasic pills, skipping placebos and continuing with the next month's dose can make

a woman more likely to experience spotting or breakthrough bleeding.) In 2003, the U.S. Food and Drug Administration

(FDA) approved low-dose monophasic birth control pills that induce withdrawal bleeding every 3 months. Yet another

version of the pill is the Loestrin Fe, which has only a four-day placebo "week" (the placebos are actually iron supplements

intended to replenish iron lost by uterine shedding); the other three placebos are replaced with active hormone pills. This

system is intended to help shorten periods. Mircette contains several days of estrogen-only pills in addition to the usual

combination estrogen/progestin pills, in the case of women who may have problems with low estrogen during the placebo

days with other pills.

Other types of hormonal birth control which affect menstruation include the vaginal Nuvaring and the transdermal patch (like the standard pill pack, active hormones are given for three weeks,

followed by a one-week break for bleeding) and the injection (which can eliminate all flow as long

as the injections are taken every twelve weeks, although spotting is a common side effect).

All such methods are designed to regulate monthly bleeding. Because of this, they are often chosen by

females who wish to regulate the frequency and length of their period, often for basic convenience and

especially when such factors are irregular and problematic on their own. Hormonal contraception has also been shown to improve menstrual factors such as cramping, heavy flow, and other bothersome physical

and emotional issues related to periods.

Hormonal methods which are controlled by the user day-to-day, including pills, the ring, and the patch, need not always be used according to the standard

cycle/calendar. Their use can be rescheduled and altered in various ways to postpone or skip periods

when desired for reasons of convenience (e.g., traveling or scheduled gynecological exams), personal

enjoyment (such as expected sexual encounters or events like a wedding or dance), or health (including

very painful periods or sensitivity to hormone fluctuations). Similarly, abrupt cessation of use can

induce a breakthrough period mid-cycle.

Books

Adashi, E.Y. Ovulation: Evolving Scientific and Clinical Concepts. New York: Springer Verlag, 2000.

Grudzinskas, J.G., and J. Yovich, eds. Gametes: The Oocyte. Cambridge: Cambridge University Press, 1995.

Heffner, Linda G. Human Reproduction at a Glance. Oxford: Blackwell Science, 2001

http://science.jrank.org/pages/4950/Ovarian-Cycle-Hormonal-Regulation.html

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