2. Menstruation
  3. Understand the Menstrual Cycle and How Menstruation Works

The Mechanism of Menstruation (Menstrual Cycle, Menstrual Period)

The Mechanism of Menstruation (Menstrual Cycle, Menstrual Period) The Mechanism of Menstruation (Menstrual Cycle, Menstrual Period)

On average, a woman experiences menstruation for 35-40 years in her lifetime. Assuming there is a 5-day menstrual period each month, a woman would be dealing with menstruation for as long as approximately 6 years and 9 months in her lifetime! Now, let us review the mechanism of menstruation, which is indispensable to a woman’s body.

Supervisor: Tokyo Saiseikai Central Hospital Gynecologist, the Japan Society of Obstetrics and Gynecology specialist Dr. Nishiyama Hiroko

Why does menstruation occur?

Menstrual bleeding occurs when the endometrium peels off

Menstrual bleeding occurs when the endometrium peels off

The inside of the uterus is covered with what is called an endometrium. The endometrium grows thicker in proportion to the menstrual cycle. By the time the period just before menstruation comes, the endometrium would have become about 1cm thick.

When we say lining membrane, some people may imagine something like a wall; however, in fact, it is a kind of tissue that includes the cell, capillary, and secretory gland that produces the secretory fluid.

Once menstruation begins, a tissue of the intima’s surface called stratum functionale peels off and starts to bleed. As this endometrium is destroyed, enzyme is produced. This enzyme works to destroy the coagulation factor, which makes the blood harden. As a result, it goes out of the body as menstrual bleeding. However, when there is a lot of bleeding, the function of the enzyme is insufficient; thus part of the blood becomes hardened, and becomes a cause of dysmenorrhea (→Introduced in ”Menstrual pain (Period pain)”).

To put it simply, menstrual bleeding comes from the endometrium as it is peeled off from the uterus and dissolved to flow out. Under the functional layer that came off, there is a part called the basal layer; and when the next month comes, it forms a new tissue and makes the lining membrane thicker. Thus the monthly cycle in which the endometrium peels off and flows out, and then forms a new tissue again is caused by female hormones. This is repeated inside the uterus every month.

When does menstruation start, and when does it end?

Female hormones have a close relationship with their first menstruation and menopause

The average age of first menstruation is 12.3 years old, and menopause is 49.5 years old.

The amount of secretion of female hormones gradually increases from around the age of 7-8 years old and keeps increasing after first menstruation until around the age of 20. When a woman is in her twenties, secretion of female hormones reaches its peak and she becomes physically ready for pregnancy and childbirth. When a woman reaches her late thirties, secretion of female hormones starts to decrease; in time she will come to see a menopause, and secretion of hormones will cease. It takes approximately 10 years before a woman becomes completely apart from female hormones, with menopause coming in between.

The cause of abdominal pressure-induced incontinence is looseness of the pelvic bottom muscle supporting the pelvis of women. Various organs such as the uterus, vagina, ovary, bladder, urethra, rectum, etc. are located inside the pelvis of women. The muscle at the pelvic bottom, the pelvic bottom muscle firmly supports those organs from the bottom. But when the pelvic bottom muscle weakens, the bladder cannot be supported, causing it to go down and thus change the shape of the urethra. In such cases, urine leakage can happen easily.

Female hormones have a close relationship with their first menstruation and menopause Female hormones have a close relationship with their first menstruation and menopause

First menstruation age, menopause age graphs: Japan Society of Obstetrics and Gynecology, “Obstetrics Gynecology Glossary/Term Revised Edition” Revised 3rd Edition

First menstruation precursors

The breasts begin to grow little by little, forming a roundish, feminine build on the whole. At the same time, hair begins to grow in the underarms and pubis, and vaginal discharge begins.

In contrast to the rapid physical changes, the mind cannot keep pace with such changes; causing a gap in the development of the body and mind. Being unable to adapt to the gap, a person in this period of age (adolescence) has various troubles.

Signs of menopause

Menopause does not necessarily mean that you suddenly stop having menstruation. Your menstrual cycle may be delayed by 2-3 months, or become disorderly; for example, your menstruation might come twice a month, or there is increase/decrease in the amount of menstrual bleeding, or you may have small amounts of menstrual bleeding that goes on for 2 weeks. These are all due to instability in the secretion of estrogen. You may be mentally irritated or you may be attacked by a sense of uneasiness. In general, it is said that your menstrual cycle becomes shorter, then longer, and finally comes to a close.

Why does menstrual bleeding go on for days on end?

The reason why menstrual bleeding does not come all at once, but takes a few days has something to do with the size of the uterus and the amount of hormones that are secreted each month. It is also concerned with the size of the orifice of the uterus. The entrance of the uterus is a very thin, small hole that is thinner than that of a straw. Thus, it would take a certain amount of time for blood to get through.

During menstrual period, the uterus contracts to squeeze out the blood inside, just as you would do when you squeeze the paint tube to get the paint out.

The position of the uterus affects the way the blood flows out, too. Normally, it is positioned in an angle which would make it easy for blood to flow smoothly; however, if the uterus is tilted a little too much to the front or back, it would make it hard for blood to flow. In that case, bleeding would linger sluggishly, or even take a break before it starts bleeding again in increased amounts in the latter half of the period.

The menstrual cycle and mental and physical changes

What is a favorable menstrual cycle?

A menstrual cycle is the cycle that begins with the first day of menstruation until the day before you get your next menstruation. A normal menstrual cycle is 25-38 days; those with a shorter cycle within 24 days are called polymenorrhagia; and those with 39 days or more before the next period are called oligomenorrhea.

Moreover, a favorable menstrual period is 3-7 days, but the menstrual period that ends within 1-2 days is called a too-short menstruation, and the menstrual period that lasts more than 8 days is called a prolonged menstruation.

Menstrual cycle and fluctuations in endometrium and hormonal secretions

The menstruation period

When the ovulated egg and sperm are united to become a fertilized egg, and the fertilized egg is imbedded in the endometrium, pregnancy is achieved. When pregnancy has not been achieved, secretion of both the progesterone and follicle hormone decreases. The endometrium that is no longer necessary will peel off, and will be discharged outside the body along with blood. (Menstruation)

Proliferative stage (Preovulatory phase)

Due to the function of estrogen, one of the primordial follicles in the ovary starts to develop. As the ovarian follicle develops, estrogen is secreted, and the endometrium becomes gradually thicker.

Ovulatory phase

When secretion of estrogen reaches its peak, luteinizing hormone is secreted, and the ovule pops out of the ovarian follicle (ovulation).

Secretion stage (Luteal phase)

The ovarian follicle after the ovule has popped out becomes a tissue called the corpus luteum, where progesterone is secreted. In preparation for the imbedding of the fertilized egg, the endometrium becomes soft.

A possible ovulatory pain during the ovulation period

Various changes occur in the female mind and body concurrently with the menstrual cycle. The mid-period between menstruations, or the 2-3 days prior to or after ovulation day is a period in which the amount of vaginal discharge is largest in quantity; and this is called the ovulation period.

Some people may have pain called ovulatory pain during the ovulation period. This is thought to occur when the ovarian follicle, which has developed to face ovulation, stimulates the peritoneum; or when there is a wound or bleeding from when the ovule pops out of the ovary.

If the pain is tolerable, there is no need to worry. However, the pain differs by individual, and to some, it is just as painful as menstrual pain. If the pain is strong, you may need treatment. You should measure your basal body temperature and record the period of pain as well as its condition before seeing the gynecologist. Furthermore, in some cases, during the ovulation period, the quantity of estrogen may decrease temporarily, and interval hemorrhage may occur.

Before menstruation begins

This is a period in which both the body and mind become uneasy. Due to premenstrual syndrome (PMS), symptoms may be found easily where the breasts become tense, hurt, the nipples become sensitive, feel headache, shoulder stiffness, low back pain, have diarrhea, acne vulgaris, rough skin, irritation, depression, sleeplessness, sleepiness, overeating.

What are the causes for menstruation being late?

What are the causes for menstruation being late?

If there is no sign of menstruation after 1 week from the expected menstrual date, it’s late

A normal menstrual cycle is supposed to be 25-38 days. Although it varies by individual, the cycle is repeated every month according to a stable cycle. If such menstrual period comes late by a few days, and your physical rhythm is upset, you may feel anxious.

Menstruation tends to be affected by your physical condition. Sometimes, it may start earlier or later than expected for no particular reason. You do not have to worry if it is only a small gap; however, if there is no sign of menstruation about 1 week or more from the expected date, you should consider that your “menstruation is late”.

Moreover, in order for you to recognize that your “menstruation is late”, you would need to know your menstrual cycle. You should have a perception of your menstrual cycle by keeping record of it, whether it is to write down in your calendar or notebook, or to use an apps; whichever way that suits you will be fine.

[Reasons for menstruation delays (other than pregnancy)]

  • Mental stress
  • Irregular lifestyle
  • Unrealistically extreme diet
  • Overweight
  • Unbalanced meals
  • Not enough sleep
  • Not enough exercise

What are the causes for menstruation being late?

The fact that menstruation comes periodically means that the female hormones are working normally. On the contrary, when menstruation is delayed, this might mean that female hormones are not being properly secreted due to the various reasons mentioned above.

When significant physical burdens such as overtime work late at night, chronic sleep deprivation, sharp weight loss by going on a diet and unusually hard exercise is imposed on the body, the latter gives priority to its own protection and tries to postpone the functions relating to reproductive functions. As a result, ovarian functioning decreases and menstruation is delayed.

What are the causes for menstruation being late?

Also, if you feel a significant amount of stress while at work or have troubles in relationships with people, an abnormality occurs in the hormonal center inside the brain which causes the orders from the brain not to be properly conveyed to the ovaries. Therefore, the function of the ovaries is reduced, and the menstruation rhythm becomes unbalanced.

If menstruation is delayed, the best thing to do is eliminate possible causes. Just by removing stress factors on the body such as making efforts to have balance and regularity in your life, eating nutritiously and getting enough sleep can help start menstruation that was delayed.

For mental stress, find a way to solve it yourself, such as having a slow and relaxing bath, cover yourself with your favorite aroma or fragrance etc., allowing you to get rid of it little by little.

The Source of Problems during Menstruation, and How to Deal With Them

Lower Abdominal Pain

During menstruation, prostaglandins are secreted from the uterus and act to release the fallen endometrium as menstrual blood leaves the body. If a lot of this substance is secreted, contractions in the uterus tend to become excessive, which leads to increased pain. Also, stress and the cold can also lead to increased pain, since the cold causes blood in the pelvis to stagnate and stress causes blood circulation to deteriorate.

Lower Back Pain

As menstruation begins, a type of ovarian hormone called relaxing is secreted and the pelvis opens up in order so that menstrual blood can flow more easily. Since this hormone affects the muscles around the pelvis and the waist, lower back pain can occur. Also, hormonal imbalances, stress, and cold weather can also cause poor blood circulation in the pelvis. So as mentioned before, an excess of prostaglandin can also lead to lower back pain.

The Source of Problems during Menstruation, and How to Deal With Them


Since prostaglandin acts on the stomach and intestines along with the uterus, nausea may occur when this substance is secreted in high amounts. Nausea may also occur since menstrual cramps can cause a lack of hunger, which then puts a strain on the gastrointestinal tract due to unbalanced eating patterns.

Solutions: If nausea interrupts your daily schedule, please allow yourself to take a medicine that suppresses the secretion of prostaglandins. Generic medicine may be ineffective, so seeing a gynecologist would be better. If your nausea is less severe, consuming foods that prevent this may help: for example, like ginger and mint. If your appetite decreases, drinking hot water with ginger or mint tea may be helpful. An empty stomach can also lead to stronger nausea, so eating something is important. Please consume foods that your stomach can digest and absorb well.


During menstruation, luteinizing hormones are secreted. This leads to suppressed contraction of the uterus from before ovulation starts to after ovulation finishes. The luteinizing hormone also leads to suppressed contraction of the intestines, so constipation is a common side effect. When menstruation begins, constipation is less likely since the luteinizing hormone decreases. However, the secretion of prostaglandin causes the intestines to contract, which makes diarrhea more likely to occur.

Solutions: When experiencing diarrhea due to menstruation, it is vital for the body to stay warm. Please wear warm clothing, especially around the abdomen. Eating certain fruits and beans may also lead to diarrhea since they store moisture in the intestines and contain saccharides. So please do not consume these foods, along with coffee and cold foods and drinks. If diarrhea is a concern when going out, please bring a pill that can control diarrhea and be consumed without drinking water.


From before ovulation to after ovulation, a luteinizing hormone is secreted which has an effect of suppressing the contraction of the uterus. Luteinizing hormone also suppresses the contraction movement of the intestines, so it becomes easy to become constipated at this time. When menstruation begins, luteinizing hormones decrease, so symptoms of constipation are improved, but the secretion of prostaglandin causes the intestines to contract and diarrhea easily occurs.

Feeling Depression

Luteinizing hormones and estrogen affect the heart along with the body. Before menstruation occurs, the secretion of luteinizing hormones can lead to feelings of irritation and depression since this hormone tends to throw emotions off-balance. In addition to this, physiological changes like menstrual pain and discomfort in delicate parts of the body can also lead to depression.

The Source of Problems during Menstruation, and How to Deal With Them

Solutions: When feeling irritation and depression, please do not put more mental or physical stress on your body than necessary. Get plenty of sleep, eat balanced meals and keep your body warm so that the hormonal rhythm of your body isn’t disrupted. Make an attempt to remove any sources of stress in your daily life. Some strategies for doing this are going to karaoke and singing loudly (which can get rid of irritation), listening to music you like, drinking herbal tea, and relaxing. To avoid stress and recover from mental and physical fatigue, relaxation is important. 


There are two different types of headaches that can occur due to menstruation. One type can be characterized by a sort of throbbing and pulsating pain, and the other can be characterized by muscle tension in the neck and shoulders that leads to a migraine. These headaches can occur due to the stress and fatigue brought on by menstruation.

Solutions: When experiencing a headache due to menstruation, expanding blood vessels in the brain are causing that pain, so applying something cool to the temple and holding it there will help to soothe the flow of blood vessels. Exposure to light or sound may also increase pain, so closing your eyes and lying down in a dark, quiet room may help. Headaches that occur due to muscle tension should be treated by heating the back of the head, neck, and shoulders – along with any other sensitive parts of the body – with a steamed towel or by lightly stretching your neck and arms while moving them around. This helps to improve blood circulation by loosening the muscles. 


During menstruation, anemia can occur due to a lack of blood heading to the brain. Instead, it heads to the uterus, and as the supply of blood heading to the brain decreases, the amount of hemoglobin – which carries oxygen to the whole body – also lessens.

The Source of Problems during Menstruation, and How to Deal With Them

Solutions: The recommended amount of iron for an adult woman is 10 to 12 milligrams. Iron, which is contained in hemoglobin, decreases by about 20 milligrams even during regular menstruation. Therefore, more iron should be consumed during this time. There are generally two types of iron: heme iron and non-heme iron. When it comes to non-heme iron, which is absorbed at lower rates into the body, taking vitamin C is a good idea since it boosts absorption.


Luteinizing hormones are secreted during the period from when ovulation ends to menstruation. One characteristic of luteinizing hormones is that they store moisture in the body to prepare for pregnancy. This can cause the body to swell.

The Source of Problems during Menstruation, and How to Deal With Them

Skin Issues

Before menstruation occurs, more luteinizing hormones are secreted. This, in turn, promotes the secretion of more sebum. Due to the increase in sebum, acne and pimples are more likely to come about. Menstruation is also a period when the skin is more sensitive and is more likely to be damaged, so having skin issues during this time is more common.

Solutions: During menstruation, take care to remove dirt, waste, and any extra sebum from the skin in order to keep it clean. Rich creams and oily skin products may cause further skin issues to occur, so please wash your face and maintain a moderate amount of moisture through products. Just eating more vegetables may be enough to solve any skin problems. The skin is also especially sensitive to ultraviolet rays during this time, so please take care to block any UV rays. If your normal makeup or sunscreen causes your skin to feel irritated, switching to less aggressive products may be a good idea. 


Between menstruation and the next cycle of ovulation, the estrogen is secreted, and the body enters a low temperature phase. The body enters a high temperature phase during the period from ovulation to menstruation, and more luteinizing hormones are secreted. When a person’s body temperature becomes lower, they become drowsier, and they become more alert when their body temperature rises. However, during months when even the evenings are hot, a person’s body temperature doesn’t lower that much. As a result, it can be difficult to sleep well. When a person is unable to sleep well at night, they tend to become drowsy during the day.

Solutions: Please try to increase the amount of high-quality sleep that you get. For example, go to sleep at the same time every day and do not stay up all night, exercise in moderation, take a long bath, and avoid using your TV, laptop, or smartphone before sleeping. There may be other factors to be analyzed if this drowsiness is interrupting your daily life, so if this is the case, please go see a doctor. 


During the beginning stages of menstruation and right before it starts, fatigue can occur along with swelling, chills, and poor blood circulation. Since more luteinizing hormones are secreted right before menstruation, the amount of serotonin decreases. Because serotonin has the effect of calming and regulating functions in the brain, a lack of serotonin can lead to fatigue.

The Source of Problems during Menstruation, and How to Deal With Them

Solutions: During menstruation, fatigue can be remedied by improving blood circulation, which also reduces swelling. In order to keep the lower half of your body from dropping to a lower temperature, please exercise and stretch in moderation. Be careful in regards to consuming too much sodium as well, since this can also lead to further swelling and fatigue. Eating foods that have a lot of potassium such as natto, spinach, and bananas will help to improve the metabolism and get rid of extra salt in the body. 

Under supervision of: Tokyo Saiseikai Central Hospital, Gynecologist Division; Specialist Practitioner and Professor Hiroko Nishiyama of the Obstetrics and Gynecology Society of Japan

The scientifically correct term for menstruation is referred to as “menstrual period.” However, the term menstruation will be used here for ease of comprehension.

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