The monthly cycle governing a female's fertility, usually from 21-35 days, and often following the lunar tide. During the bleeding phase of the cycle (3-5 d.) the lining of the uterus is sloughed off. Approx. 2 wks later, ovulation occurs and the period of a female's greatest fertility (3-5 d). Usually beginning at age 13 and ending around age 50, but this varies greatly.

The time when a girl first starts having periods (menstrual cycles) is called menarche. This commonly happens at around 11 +/- one or two years but has been known to happen as early as 8 and as late as 17.

The point at which a woman stops having periods naturally as her ovaries stop releasing eggs is known as menopause. This typically occurs somewhere between 40 and 60 years of age.

What every man should know about a woman's menstrual cycle.

In the years I've spent so far in college, one of the beneficial things I have been able to experience is developing closer relationships with members of the opposite sex as well as living within close proximity of them. This, for me, has meant getting to know guys. ..

and also discovering that most of them are quite ignorant when it comes to the subject of a woman's menstrual cycle. For whatever reason, the junior high school health class and the portion often referred to as "sex ed" seems to have failed to convey even the most basic facts. This may be related to a more general problem in middle school education, but that's another issue. When it comes to the truth about a woman's menstrual cycle, guys who have sisters and girlfriends are sometimes slightly more knowledgeable in this subject. But this is important stuff that everyone ought to be aware of because at some point in your life it is likely to affect in you in some way.

1. the BASIC basic

The root of the words menstruation, menstrual, menopause, etc. is mensis - Latin for month.
see Webster 1913's dictionary entry of menstruation here

At birth, females have all the eggs their bodies will ever use and more, perhaps as many as 450,000. Males produce sperm throughout their lives, but females have what they started out with. The eggs are stored in a woman's ovaries, in sacs called follicles. As a girl approaches puberty, her body produces hormones that cause the eggs to mature. This is where it all begins. etc. etc...

Actually, there are a lot of things that one could learn about menstruation. One could find out about the intricate details of the female reproductive system and the biological functions involved in the process. But I'm going to concentrate on the the most important and practical stuff to know.

a brief anecdote :
This is a true story, an exchange which happened between a couple friends of mine, who will remain nameless.

Girl receives phone call from Guy at 7:30 in the evening. Guy says to girl, "Hey, a bunch of us are going swimming, you wanna go?" Girl: "I can't go, I'm on my period. Guy: "Oh. Alright. Bye." Guy hangs up the phone. End of first conversation. A half an hour later, Girl receives a second phone call. Guy: "Hey, we're supposed to meet at the pool at 8:00, I'll come pick you up, okay?" Girl: "HELLO! I already told you ...___________. Guy responds, "What? Aren't you DONE yet?" ...
What happened later that week was Girl decided to find out what guys know about the menstrual cycle. She decides to ask to see what guys know. Girl asks a guy (different guy from Original Guy) how long he thinks it lasts. His reply? "I dunno.. 15 minutes?"

Grossly uninformed.

A woman's entire menstrual cycle is the process of ovulation, which lasts an average of 28-30 days. This is why menstruation happens about every month (though it may not be so regular for each individual). Average time menstruating for most girls is probably around 4-7 days.

2. the PMS thing

Most guys have probably heard of PMS. PMS stands for premenstrual syndrome. It refers to the changes that a woman's body undergoes in the few days (although it can be up to two weeks prior) before her period begins and lasts through the duration. Hormonal levels and neurochemical changes in the brain can result in a combination of the following: breaking out (skin trouble), bloating (a generally unpleasant feeling), abdominal cramping, headache, migraine, fatigue, constipation, painful joints, backache, cravings for certain foods, heart palpitations and weight gain.

You will probably hear the most complaints about cramps, since it tends to be the most severe symptom in bad cases. For me, cramps mean wanting to curl up in the fetal position and lie on the floor. The intensity and actual experience of cramping varies greatly from person to person. Some girls don't really get cramps and others of my friends are rendered unable to function at all for a day or so. However, like most PMS symptoms, YMMV from one female to another. Emotional and behavioral changes may include anxiety, depression, irritability, panic attacks, tension, lack of coordination, decreased work or social performance and altered libido. Advil or Midol can help relieve some of symptoms and most women do not experience all of them. Thank goodness.

A side note about PMS, it is a GOOD thing to be sympathetic to women and try to understand what she may be going through at that time of the month. I should say, however, that attributing any and all mood swings or emotional highs/lows to PMS is definitely a BAD thing to do. If a woman says something you don't agree with, or you accuse her of being irrational and blame her behavior on PMS or it being that time of the month, you will be inviting all kinds of wrath upon yourself.

3. feminine products

There are various options available to women in order to handle the main physical aspect of menstruation -- bleeding. The two most commonly used are the pad and the tampon. Both come in differing sizes, so that women can select one that fits their needs in terms of flow (light to heavy). Pads function sort of like a diaper (a much smaller one) for catching the fluids. They can, however, be bulky and a hassle to move around or play sports in. For this reason, many prefer tampons. Tampons sit in the vaginal cavity and if inserted properly, cannot be felt at all. Otherwise, there may be discomfort. Their function is to absorb menstrual flow before it comes out.

Nevertheless, with both pads and tampons, accidents do happen, products may not do their duty and things may leak. And blood stains. Thus, it is good to keep some hydrogen peroxide around (it helps get out the stains) and leather seats in your car are a bonus! Additionally, if a need should ever arise and you are willing to help a girl out by buying said feminine products for her, it is likely that you will be praised for your valour and confidence in your manhood.

4. a final note

Being considerate and sensitive to underlying things which may be going on within a woman's psyche is a skill worthwhile to learn. It is not required that you constantly discourse with females about everything mentioned above. They will probably find it strange if you do. But feel free to ask any genuine questions you may have, most women will probably answer to the best of their abilities and view the fact that you have thought about woman issues at all as being a good thing. Anyway, good luck!

If women are supposed to be less rational and more emotional at the beginning of our menstrual cycle when the female hormone is at its lowest level, then why isn't it logical to say that, in those few days, women behave the most like the way men behave all month long?

Gloria Steinem

I've always felt sorry for boys, biology-wise. They definitely got the bum end of it in terms of interesting hormonal reflexes. The female menstrual cycle has been constantly revised in my education since I was 8; year after year we'd return to it in Biology and learn a little bit more about its intricacies. Girls, of course, had the upper hand; we get the joy of having to experience this knowledge in a practical setting once a month. Boys just sat there, clueless. And excluded... I didn't get taught about the process of spermatogenesis till I got to my first year of university. If you were to ask the average girl what she knew about her reproductive affairs, she could give you the basic ins and outs of it. Ask your average boy (and I have) what their gonads do, and the best they can (usually) come up with is some sexual innuendo along the lines of "rock your world, baby!" That quote there is courtesy of a long, long ago ex. I tend to pick the cute-but-dumb ones.

So, to redress a balance, in this write-up of the female menstrual cycle, I will drop in occasional pearls about the male gonads, which are a lot more interesting than the secondary school educational system would have you believe.

Menarche

'Gonads' are the primary reproductive organs in the body; ovaries for girls and testes for boys. Whilst boy's testes produce sperm continually from puberty until death, girls are born with their ovaries already containing all the eggs that they'll ever use in their lifetime. Which is quite a whacky concept if you think about it; when your mum was incubating in your grandmother's womb, half of you was in there as well. How cool is that?

As a girl grows, her ovaries gradually mature. They secrete minute amounts of oestrogen all this time to inhibit the release of gonadotropin-releasing hormone (GnRH), which is the hormone that causes the release of other hormones that stimulate ovulation. This state of affairs continues until a girl is around 8 years of age; from this point forward, GnRH levels will gradually start to rise, triggering the development of secondary sexual characteristics. About three years after this, a girl will experience menarche: her first menstrual period. Of course, this isn't set in stone; some girls will have their first period aged 9, some will have it aged 17. If her first period occurs either before or after this age range, then it indicates that there may be something medically wrong that needs further investigation.

The ovarian cycle

The ovarian cycle is different from the menstrual cycle; the ovarian cycle describes the hormonal development of the oocyte (egg cell) and the menstrual cycle describes the development of the lining of the uterus. However it is beneficial to consider one before looking at the other. The ovarian cycle is only complicated if you think of it being complicated. That's what I tell myself come exam time anyway. It's regulated by five hormones: GnRH, luteinizing hormone (LH), follicle-stimulating hormone (FSH), oestrogen and progesterone. Each cycle takes approximately 28 days to complete; the normal range is considered to between 21-35 days. It is a commonly held misconception that a woman's period will coincide with the phases of the moon; not so. If it were that predictable, life would be a lot easier. Not all women are as regular as clockwork; one cycle may take 25 days while the next takes 32. Of course, some women are as regular as clockwork and are guaranteed to come on at 7am every fourth Sunday.

Fun Fact #1: men use exactly the same hormones in the production of sperm, except for a substitution of testosterone for oestrogen and progesterone. It takes men approximately 16 days to work through their hormone cycle, which means they have nearly twice as many 'PMT' episodes per year than women. Stick that in your pipe and smoke it.

At birth, the ovary is packed full of potential egg cells (around 2 million), only a fraction of which will ever see the light of day; a lot die off before puberty, with only 400,000 primary oocytes remaining at menarche, and only about 500 ever completing the ovarian cycle. The number of viable ova continue to diminish as a woman ages, by 30yrs there's only 100,000 left, and by the age of 50, it's down to just 3 (Marieb, 2001). At the beginning of the ovarian cycle, the primary oocytes are stimulated by GnRH, FSH and LH to begin developing from a primary oocyte into a primary follicle, which begin secreting oestrogen. The follicle then further develops into becoming a granulosa cell, and then into a theca folliculi. By this point it's secreting enough oestrogen to initiate a negative feedback cycle on LH and FSH, inhibiting their production. The folliculi continues to develop, and begins to bulge out of the side of the ovary. It is around this time that meiosis I occurs, which results in the formation of a secondary oocyte, and a polar body (the 'junk' potion of meiosis I).

Fun Fact #2: In males, meiosis produces four gamete cells (sperm), in contrast to female meiosis, which only produces one gamete (egg).

By now, the folliculi is producing so much oestrogen that a positive feedback cycle is initiated for LH and FSH; remember, a little oestrogen has a negative feedback, a lot of oestrogen has a positive feedback. Craziness. This occurs around day 14, and this sudden surge of LH, FSH and oestrogen causes the folliculi to burst, releasing the secondary oocyte into the fallopian tubes. Some women experience pain when the folliculi bursts; in German, this pain is call mittelschmerz, or "middle pain", and is caused by the stretching of the ovarian wall during ovulation. Only 1-2% of ovulations produce more than one egg (which, if both are fertilised, will produce fraternal twins). Secondary meiosis (meiosis II) will only occur if a sperm fertilises the secondary oocyte; the sperm only have a 12-24hr window to reach their target, so it's quite a tight schedule. The more I discover about the process of procreation, the more shocked I am that the human race still exists.

Fun Fact #3: Women usually produce only one gamete every ~28 days. Men produce 400million a day. That's 4,700 a second. I often present this fact to a member of the opposite sex, and this is the point where I start counting: 4,700 mississippi; 9,400 mississippi; 14,100 mississippi; 18,800 mississippi; 23,500 mississippi... Poor boys. You must feel permanently drained by all that genetic division.

The ruptured folliculi left in the ovary is now stimulated by the LH surge to collapse down and form the corpus luteum, a "yellow body" in the ovary that secretes oestrogen and progesterone to maintain the lining of the uterus in preparation for implantation of an embryo. FH and LH secretion is once again inhibited by the lower levels of oestrogen until the end of the cycle, when the whole merry dance starts again. If implantation does not occur, then the corpus luteum dies, causing the lining of the uterus to shed, which brings us very nicely around to...

The menstrual cycle

The menstrual cycle describes the monthly preparation of the uterus for implantation of a fertilised ovum. The uterine endometrium in its normal state is not, in itself, all that hospitable to receiving an egg, so it has to develop a lining that is. Like the primary follicles, the uterine endometrium responds to changing levels of hormones, and so is coordinated with the phases of the ovarian cycle. Assuming a 28-day menstrual cycle, it goes something like this:

Days 1-5 – This is the menstrual phase; the portion of the cycle where the lining of the uterus sloughs off, resulting in a menstrual period, or menses, where a woman bleeds for 3-5 days. By day 5, the growing primary follicle is starting to produce oestrogen. Days 6-14 – This is the proliferative phase; the portion of the cycle where the uterine endometrium starts to rebuild itself, stimulated by the rising levels of oestrogen being released by the primary follicle. The basal layer of the endometrium generates a glandular layer that slowly thickens. This new layer is supplied by spiral arteries, which gradually increase in number. They are literally shaped like spirals, which allows them to grow with the new lining as it thickens. By day 14, the lining is thick and velvety, and very well vascularised; the perfect place to grow an egg. The steadily growing levels of oestrogen have stimulated the receptor cells of the endometrial lining to produce receptors for progesterone. When ovulation occurs on day 14, the corpus luteum develops and starts to produce large amounts of progesterone and oestrogen, preparing the lining for implantation. Days 15-28 – This is the secretory phase; this is where the endometrium prepares itself for the implantation of an embryo. The progesterone acts on the endometrial lining, causing further proliferation of the spiral arteries, and for a secretory mucosa to develop that releases nutritious glycoproteins that'll keep the embryo fed until full implantation has occurred. If fertilisation has failed to occur, the corpus luteum will slowly begin to die off, causing a drop in the release of progesterone. Since progesterone is the hormone that maintains the endometrial lining, as the progesterone decreases, the lining will start to degrade and self-digest. On day 1, it will start to slough off, and the cycle starts again. However, if fertilisation does occur, the embryo will release human chorionic gonadotropin (hCG), which maintains the corpus luteum, thus also maintaining the endometrial lining.

The menstrual cycle is exactly that; a cycle. This will keep on repeating itself until either pregnancy, where it takes a break for nine months; or until the ovaries run out of eggs. This point is called menopause, and will usually occur around the ages of 45-55.

Menstrual abnormalities

There are many, many different problems that can affect a woman's menstrual cycle; this is why gynaecologists earn so much. It's pointless to go through each one (not least because there's so many of the damn things), but a list of medical terminologies that are used to describe abnormal menstrual cycles is:

• Menorrhagia – a prolonged and increased menses
• Metrorrhagia – regular intermenstrual bleeding, i.e., bleeding that occurs outside of menses
• Polymenorrhoea – menses occuring with <21day intervals
• Oligomenorrhoea – menses occuring with >35day intervals
• Hypermenorrhoea – excessive regular intermenstrual bleeding
• Menometrorrhagia – prolonged menses and intermenstrual bleeding
• Amenorrhoea – absence of menses for >6mths.

Reference

• Marieb E N, 2001,"Human Anatomy and Physiology", 5th edition, Addison Wesley Longman

The nodes above give a detailed classic view of how the menstrual cycle works. Something to add to this, however, would be how the hormones released during the menstrual cycle are the driving force within itself.

Hormonal Control of the Menstrual Cycle:

• Follicular phase—several follicles in the ovaries grow and secrete extra estrogen due to follicle-stimulating hormone (FSH) from the anterior pituitary.
• Ovulation—secondary Oocyte ruptures out of the ovaries due to luteinizing hormone (period).
• Luteal phase—is when the corpus luteum forms from the follicles left behind and secretes estrogen and progesterone, thickening the endometrium of the uterus.
• Menstruation—is the monthly shedding of lining of uterus when implantation of an embryo doesn't happen.
• FSH—synthesized and secreted by gonad tropes, promotes the maturation of germ cells into sperm cells and eggs.
• Gonad tropes—cells in anterior pituitary which produce LH and FSH.
• Anterior Pituitary—is controlled by the hypothalamus in how much of which hormone it produces (is a hormone producing gland).
• Oocyte—is an egg before maturation.
• Oogenesis—is the process of producing oocytes which can then become either spermatozoa or an ovum depending upon the sex of the organism, through meiosis.
• Luteinizing Hormone (LH)—hormone synthesized and secreted by gonad tropes in the anterior pituitary gland. An acute rise in LH triggers ovulation.
• Corpus Luteum—is produced during luteal phase of the menstrual cycle from an ovarian follicle, secretes progesterone and estrogen to thicken the endometrium after shedding.
• Estrogen—produced by follicles in the ovaries, corpus luteum, FSH and LH, thicken the wall of the endometrium and other regulatory methods during the menstrual cycle.
• Progesterone—causes the endometrium to switch to secretion stage to prepare the uterus for implantation. If pregnancy does not happen, progesterone levels will decrease and lead to menstruation.
• Endometrium—is the lining for the uterus which prevents adhesion between different walls in the uterus.
• GnRH—triggers the release of FSH and LH from the anterior pituitary as synthesized and released by the hypothalamus.
• Hypothalamus—regulates some metabolic processes and synthesizes and secretes neurohormones, which signal the anterior pituitary gland to secrete certain hormones.

Overall, the menstrual cycle as controlled by hormones is as follows. The hypothalamus controls the secretion of hormones by certain cells throughout the body. Specifically during the menstrual cycle, the hypothalamus produces "messenger hormones," or neurohormones, which trigger the secretion of luteneizing hormone and follicle stimulating hormone, each of which are important chemicals controlling the feedback loop that is the menstrual cycle.

The menstrual cycle has 2 phases, the follicular phase and luteal phase. During the follicular phase, estrogen is released by follicles in the ovaries, which in turn stimulates the secretion of LH from the anterior pituitary. This will happen until the follicle fully matures and ovulation happens. At this point, the luteal phase occurs, in which LH causes the corpus luteum to release progesterone and estrogen. The levels of these two hormones will then reach a point at which the hypothalamus and pituitary gland will turn off, lowering the amounts of LH and FSH present.

Estrogen and progesterone secretion are caused by a rise in follicle stimulating and luteneizing hormone. The rise in FSH and LH are caused by the decrease in estrogen and progesterone. This coincides with the menstrual cycle, in which at ovulation, FSH and LH are at a high and estrogen and progesterone are at a low. The turning being ovulation, is the point at which FSH and LH decrease and estrogen and progesterone increase.