What is a menstrual period? Important Information

what is a menstrual period?

what is a menstrual period?

The menstrual cycle (cycle) is a chain of events that lasts from the first menstruation (menarche) to the last menstruation (menopause), characterized by menstrual bleeding, the purpose of which is the continuation of the lineage with reproduction and affects the whole body. When the menstrual cycle or menstrual period is mentioned, what is meant is the period from the first day of one menstrual bleeding to the first day of the next menstrual bleeding. When the menstrual period is mentioned, the period with bleeding or the period without bleeding is not understood.

What is the normal cycle (cycle)?

The normal cycle is a period of 21-35 days (mean 28 days), bleeding between 2-8 days and characterized by 20-80 ml of bleeding.

The menstrual cycle is a complex cycle controlled by the brain-ovaries-uterus system.

How many periods is the menstrual cycle (cycle) divided into?

To understand this, first of all, it is necessary to examine the events in the body during the menstrual cycle.

Starting from the moment of adulthood, a hormone called GnRH is secreted from the hypothalamus region of the brain. This hormone stimulates the pituitary gland in the brain, and the hormones FSH and LH are secreted from there.

These hormones mix with the blood in different ways at different times of the menstrual period and start the development of egg cells by stimulating the ovaries.

Again, under the influence of these and some other hormones, hormones called estrogen and progesterone are secreted from the ovaries. Estrogen secreted more than these two hormones causes the endometrium, which is the inner membrane of the uterus, to thicken.

Only 1 of the developing egg cells (follicle) reaches full maturity and when the appropriate hormonal environment is formed, it cracks and ovulation occurs.

This is called ovulation.

After ovulation

After ovulation, more progesterone hormone begins to be secreted from the ovaries. Progesterone stops the endometrium from thickening but allows it to mature. The egg cell released as a result of ovulation is snatched by the tuba and begins its journey towards the uterus. In the meantime, if fertilization occurs, the resulting embryo attaches to the endometrium prepared by the hormones and pregnancy occurs.

If fertilization, that is, pregnancy, does not occur, the amount of hormones gradually decreases, and as a result, when it falls below the level that protects the endometrium, the thickened endometrium begins to shed with bleeding and is thrown out into the vagina. This is menstrual bleeding. Then this cycle continues until menopause, that is, until the egg cell is depleted in the ovaries.

The part of the menstrual period until ovulation is called the “follicular phase” because the follicles develop in the ovaries, or the “proliferative phase” because the endometrium thickens. The period after ovulation is called the “luteal phase” or “secretory phase”.

What are the necessary conditions to see menstruation?

Hormones must be secreted from the brain

In response to the hormones secreted from the brain, hormones must be secreted from the pituitary gland.

There should be follicles in the ovaries and these follicles should be capable of secreting hormones.

Endometrium must be present and sensitive to these hormones

There should be no anomaly that would prevent the resulting blood from flowing out.

At what age does the first menstruation occur?

It is not possible to know for sure at what age the first menstruation, which is the last stage of the transition from childhood to adolescence, will occur. This may vary according to breeds and environmental factors. The first menstruation is usually between the ages of 11-14 in our country.

If menstruation has not been seen until the age of 16 and there are no signs such as breast enlargement, pubic and armpit hair growth, which are called secondary sex characters, it would be beneficial to contact a gynecologist.

Some authors say that in cases where secondary sexual characteristics develop, it is possible to wait until the age of 19 for the first menstruation. In the period after the first menstruation, the cycles become irregular. In these cycles, there is usually no ovulation (anovulatory cycle). Sometimes bleeding occurs twice a month, sometimes every 3-4 months. These are all normal. It may take up to 2 years for menstruation and ovulation to settle down.

Events in the ovary during the menstrual cycle

At the beginning of each menstrual cycle, one of the ovarian cells located close to the outer surface of the ovary in one of the ovaries enters the maturation process with the effect of the FSH hormone secreted from the brain.

During this process, the maturing egg cell is in a sac filled with a clear fluid, called a follicle.

Initially a few millimeters, the follicle reaches a diameter of 16-20 millimeters near the middle of the menstrual cycle.

The estrogen hormone, which is secreted in increasing amounts from the first days of the menstrual cycle in the follicle,

is produced in greater amounts as the follicle matures and grows and passes into the blood. When estrogen in the blood reaches its highest level, it stimulates the secretion of luteinizing hormone (LH) in the brain.

LH secretion

LH secretion increases rapidly in as little as 12 hours and reaches its peak. With this rapid increase in the level of LH hormone, the mature follicle structure cracks at its thinnest point and releases the egg cell inside. This event, which takes place on the 14th day in a woman with a 28-day menstrual cycle, is called ovulation.

The released egg cell is caught by the fringes of the adjacent Fallopian tube and taken into the tube.

The fallopian tube is in contact with the abdominal cavity at the fringes and with the intrauterine cavity at the other end.

The active movements of the fringes prevent the egg cell from falling into the abdominal cavity,

and the egg cell entering the tube moves towards the intrauterine cavity inside the Fallopian tube with the help of special “hairs” that allow movement in one direction, called cilia in the tube.

After the follicle cracks, a structure called the Yellow Body (lat: Corpus Luteum) is formed in the “fracture zone”

and this structure begins to produce the hormone progesterone.


When pregnancy occurs, the Yellow Body continues to secrete progesterone hormone until about the 10th week of pregnancy in order to provide hormone support to the baby.

From the 10th week, the baby becomes able to produce its own progesterone hormone and takes over the task.

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If pregnancy does not occur, the function of the Yellow Body ends in 14 days and the yellow body regresses.

With the cessation of the hormone secretion of the Yellow Body, the level of progesterone hormone in the blood drops in a short time, and this causes the “destruction” of the inner layer of the uterus by losing its support. This “breakdown” happens with menstruation, and the “destroyed” tissue is expelled from the body along with the bleeding.

A new menstrual cycle begins with menstrual bleeding.

​ ​Follicular maturation in the ovarian tissue, which takes place under the dominance of estrogen hormone in the first half of the menstrual cycle,

is called the follicular stage, and in the second half,

the stage that occurs under the dominance of progesterone hormone secreted by the Yellow Body (Corpus Luteum) is called the luteal stage.

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Events that take place in the inner layer of the uterus

The inner layer of the uterus thickens with the effect of the estrogen hormone secreted from the first day of the menstrual cycle.

The progesterone hormone secreted when ovulation occurs, on the one hand, brakes this thickening effect of the estrogen hormone,

on the other hand, it directs the inner layer of the uterus to secrete some special substances,

making it suitable for the implantation of an egg cell that is likely to be fertilized and the start of pregnancy.

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In the inner clearing of the uterus, the thickening under the dominance of estrogen hormone in the first half of the menstrual cycle is called the proliferative phase (proliferation = thickening).

and the secretion under the dominance of progesterone hormone in the second half of the menstrual cycle is called the secretion phase (secretion = secretion).

Why does it bleed?

The lifespan of the Yellow Body formed in the ovary after ovulation is 14 days. As the Yellow Body “ages”, the hormone progesterone it secretes decreases.

When the progesterone hormone in the blood drops below a certain level, the inner layer of the uterus loses its support and begins to “break down”.

Because this “breakdown” is associated with bleeding, it is called menstrual bleeding.

The constant 14 days of the Yellow Body’s lifespan has a special meaning:

in a woman who has a menstrual period every 28 days, ovulation occurs on the 14th day,

whereas in a woman who has a menstrual period every 30 days, the day of ovulation is 30-14=16. day.

On the contrary, in a woman who has menstrual bleeding every 26 days, the day of ovulation is 26-14=12. day.

The picture above shows schematically the thickening process in the inner layer of the uterus,

which starts from the first day of the menstrual cycle.

The chart below shows the hormone levels formed in the body according to the days of the menstrual cycle.

Note that immediately after the estrogen hormone increases in the blood, the LH hormone also increases significantly.

It can also be observed in the diagram that the secretion of progesterone hormone is quite low before ovulation,

and increases significantly after ovulation.

Menstrual Cycle Length

The duration of the menstrual cycle, that is, the time from the first day of menstruation to the first day of the next menstruation,

is 28 days on average. While 15% of women see menstrual bleeding every 28 days, 0.5% see bleeding in less than 21 days and 1% in more than 35 days.

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The menstrual cycle is usually longer in the 5-7 year period following the first onset of menstrual bleeding. When the hormone-secreting systems mature, a regular bleeding pattern characteristic of reproductive age occurs.

Periods and fertility in the menstrual cycle :