All Journal Entries Journals
 |  Del.icio.usYahoo BookmarksFacebookGoogle Bookmarks

An Attempt to Explain the Menstrual Cycle in Plain Language

Nov 26, 2008 03:30PM - 27 comments
Tags:

menstrual cycle

,

menstrual cycles

,

ovulation

,

normal menstrual cycle

,

fsh

,

lh

,

estrogen

,

progesterone

,

conception

,

ovulation prediction

,

irregular menstrual periods

,

Womens hormones



Period Facts:

Menstruation occurs only in humans and other closely related species (like chimps).  
Other mammals have estrous cycles in which the uterine lining is completely reabsorbed by the animal. (sounds nice!)
The average age of onset of menstruation is age 12.
When counting the cycle, the first day of blood flow is counted as Cycle day 1.  
The average duration of a cycle is 28 days but any cycle length between 21 and 34 days is considered normal.  
The average duration of flow is 4 days but anything from 2 to 7 days is considered normal.
On a typical 28 day cycle, ovulation occurs on day 14.  
The menstrual period is always exactly 14 days after ovulation.  The time from period end to ovulation is variable.
A woman is most likely to get pregnant on the three days preceding or the day of ovulation.

There are four major players involved in regulating a woman's menstrual cycle:

The HYPOTHALAMUS: an area of the brain just above the pituitary gland.
The PITUITARY GLAND: a little gland that hangs from a stalk just behind the eyes.
The OVARIES: a pair of glands, each about the size of a walnut that most typically sit
     behind the uterus in close proximity to the fallopian tubes.
The UTERUS:  a muscular cavity typically the size of a pear that inhabits the space between
     the bladder and the rectum in the female pelvis.

There are five major hormones involved in creating a cycle:
(Hormones are messengers that carry messages/instructions from one tissue to another)

GONADOTROPIN RELEASING HORMONE (GnRH)
FOLLICLE STIMULATING HORMONE (FSH)
LUTEINIZING HORMONE (LH)
ESTROGEN
PROGESTERONE

What Is Happening During a Cycle?

***In the first half of the menstrual cycle--also known as the Follicular Phase:

The HYPOTHALAMUS is signaling the PITUITARY GLAND to produce FSH and LH--it does this by secreting pulses
of GnRH every hour. It also secretes a continuous small amount of GnRH, but the pulses are very  important.
The PITUITARY GLAND is producing LH which instructs the ovaries (theca cells) to produce estrogen.
The PITUITARY also produces FSH which tells the follicles (tiny cysts containing eggs) to start to grow.
Approximately 30 follicles will begin to grow.  By cycle day seven, the dominant follicle is established
and continues to grow while the other follicles degenerate. The dominant follicle will ultimately be the
only egg ovulated in this cycle. (Ocassionally there is more than one).
The OVARIES (in addition to making the follicle) are busy producing estrogen which tells the uterine lining (endometrium) to thicken and grow.
The UTERINE LINING after menstruation is very thin, only about 1-2mm thick, and will look like
a single, thin white line on ultrasound.

***At mid-cycle:

The dominant follicle is producing approximately 500 mcg of estrogen daily, it is also producing a
small amount of progesterone.  The follicle is now about 2.0 cm in diameter, and easily seen on ultrasound.
It has the appearance of a small dark fluid-filled cyst.

When estrogen levels have been this high for two or more days the LH surge is elicited--the pituitary gland
secretes a large bolus of LH. This LH surge is detectable in the urine and is the basis for ovulation predictor kits.  

There is also an FSH surge.  Rapid peaking of these two hormones signals the ovary to initiate rupture of the
follicle and ovulation of the egg.  Ovulation occurs within 24-48 hours after the LH surge.

If sperm are available at this point, now is their chance. If a sperm penetrates the zona pellucida ( a special membrane which surrounds the egg and permits only passage of Human sperm ) then fertilization occurs; if no one gets lucky, the second half of the cycle occurs.

The egg then goes on its merry way down the fallopian tube, while the follicle
from which it was expelled becomes the corpus luteum cyst. This cyst too, like the follicle is visible
on ultrasound, but has a very different appearance.

***In the second half of the cycle--also known as the Luteal Phase:

The HYPOTHALAMUS is sending out pulses more slowly--it is producing a pulse of GnRH about every
2-3 hours. Again, this is signaling to the pituitary gland to produce LH.
The PITUITARY GLAND  continues to produce higher levels of LH in the second half of the cycle than
it did in the first half.  High levels of LH signal to the corpus luteum cyst (the cyst the was produced
when the follicle burst) to produce progesterone.
The OVARY continues to produce progesterone in increasing quantities for about 7 days after ovulation.
It is also producing estrogen in high quantities. If pregnancy has not occurred, these high levels
of progesterone and estrogen signal the pituitary gland to turn off production of FSH and LH.
It is believed that the high levels of progesterone in the ovary which produced the
follicle prevent maturation of new follicles in the same ovary--in other words, if right ovary ovulated this month then left ovary will ovulate next month.
The UTERINE LINING, under the influence of high progesterone levels, has stopped thickening and
started maturing in preparation to receive the embryo (if any). One thing the uterus lining tissue
does is start to store glycogen (sugar) within the lining cells. This sugar will be released into the uterine
cavity to nourish an embryo (if any) until it can implant in the uterine wall. At this stage the uterine lining has a trilaminar (three lines) appearance on ultrasound and is about 12mm thick.

***Menstruation:

If no conception has occurred, exactly 14 days after ovulation the menstrual period will begin.
During menstruation, the uterine lining is sloughed and comes out as the menstrual flow.  
The uterus in effect, cleans itself down to the "roots" and the whole process begins again.
If pregnancy occurs, menstruation does not, but that is another story!

So, to simplify even further and summarize:

The cycle starts with menstruation. In the first half of the cycle, the ovaries are producing
estrogen which tells the uterine lining to grow.  The follicle is developing.  
At mid cycle ovulation occurs.
In the second half of the cycle the egg is sent down the fallopian tube while the cyst cavity left behind
begins to produce progesterone.  Progesterone tells the uterine lining to stop growing and start
storing up sugar for the embryo. If no conception occurs hormone production decreases and
the uterine lining is shed in the form of the next period.
Next month the follicle develops within the oposite ovary and the whole process starts over.  

Of note the whole process falls apart if no ovulation occurs, but that is another story too!

Lots more information is available at:

http://www.womenshealth.gov/faq/menstruation.cfm
http://en.wikipedia.org/wiki/Menstrual_cycle





Comments
Post a Comment
by peekawho, Nov 26, 2008 10:34PM
THANK YOU SO MUCH for this.  

by zazza, Nov 28, 2008 05:16PM
"Other mammals have estrous cycles in which the uterine lining is completely reabsorbed by the animal. (sounds nice!)"

I was expecting twins and had a miscarriage of one of the twins. I had much pain but almost no bleeding. On ultrasound afterwards one could see an empty sac where one of the twins should have been. I was told this can happen when you are expecting twins: one baby is miscarried but the other is perfectly healthy so your body does all it can in its power to release as little blood and such as possible, so as not to jeopordize the healthy baby. It reabsorbs the blood instead. I found this astonishing.

by JoyRenee, Nov 29, 2008 08:36PM
Bravo! On the pregnancy forums many women keep saying, "You'll ovulate 14 days after your period" which is NOT always true! THANK YOU!!!

by JoyRenee, Nov 29, 2008 08:38PM
Doctor, would it be possible (if you haven't already) to post this in the HEALTH PAGES in the pregnancy communities?! Or if you could give me permission to copy and paste it for you (all credit will go to you, of course). Send me a private message if you'd like for me to copy and paste it and I'll get it up. I think this is important information to have, especially from a doctor who is active on MedHelp. Thanks!

by MJIthewriter, Nov 29, 2008 09:58PM
zazza, that is really interesting what the body can do.

by LIL_LADY24, Nov 30, 2008 01:21AM
This is the best explanation ever of PMS!!!!!!!!!!!!!!!!!!!!!!!!!!

by kiaragirl, Nov 30, 2008 06:46AM
Zazza, that is what happened to me 20yrs ago when I was carrying my son....I was originally carrying twins but around week six had what I thought to be a miscarraige (well it was but only of one baby) I had contractions and small amount of bleeding on and off for 2wks...preg tests kept coming up negative but eventually had a dr test and got a bfp. When Daniel was born tho, I also "gave birth" to an empty sac which had grown to the same size as if there were still a baby in it!!!

Thank you so much for that fabulous detail of what is going on in the body during a cycle. I`m going to copy and paste it. Any chance of what happens if the egg DOES get fertilised???

by zazza, Nov 30, 2008 12:13PM
Kiaragirl,
Nice to know I have a "sister" in Ireland then! My daughter's name is Sandra and she is now in a relationship with an identical twin!
Zazza

by Texas_Bell, Dec 01, 2008 09:25AM
Thanks Dr. B.  I wish you were here in Texas.

by mg30, Dec 01, 2008 11:18AM
I had a question, I'm 29 years old and my husband and I have been trying to get pregnant but I have a very irregular period.  I get a period every 4 to 5 months if I'm lucky, but every month I get this discharge that starts off very light and ends up a little heavy where I need to use a panty liner. It's clear and at times it's egg white.   Can I still get pregnant even if I'm just discharging and what does this mean. We have a daughter so I know I can get pregnant pleast help me!!!

by se_hunnygurl_xy, Dec 05, 2008 12:26AM
Well what happens when a woman is irregular? I personally don't get my period for 5 months and then once I do I have it for a week or two. However recently I have had my period for over a month. Is there something wrong? Should I be worried?

by TammyPo, Dec 21, 2008 03:39AM
Outstanding! As you have always been.. And I agree I wish you were here in Texas Too!!!!  Tammy P

by whathell, Mar 14, 2009 04:41PM
Hey. I would ask my question n one of your forums but I'm broke and I've already paid twenty bucks to have my doctor give me a useless answer. I got the deprovera (not sure about the spelling) about three and a half months ago and I was normal for a bit but now I've been on my period for seven weeks and two days now.

I talked to my doctor and talked to a nurse a nurse at the clinic near my college, and both of them said that "irregular bleeding is normal with deprovera." First of all I think it has surpassed "irregular" bleeding. Second, even if it is a normal symptom, that doesn't make it any less terrible.

I'm anemic and I'm sleeping like all the fricking time. I can't remember anything. I caught the stove on fire this morning and I don't even have the energy to go to the gym anymore. I have Anthem insurance. How can I get them to pay for a hysterectomy? Or if you have some advice on how to stop this that would be awesome as well. Thanks

by aupinosenior, Mar 27, 2009 04:01PM
hey there doc. well im 18 yrs old and i was wondering if its normal when a person like me has her Menstrual Cycle but when i do it comes out in clots and i was woundering what i could be doing wrong because i know its not normal ..... it happened to my mom about a couple of weeks ago but she got tested and they said she had a miscarrage but i dont think that happened too me cause i proud to say im safe and i was woudering if it werent that what could it be...

by freakshow83, Jun 10, 2009 02:55PM
Hello I am 25 years old and started Ortho Tri Pills in Feb. I do have unprotected sex with my boyfriend who I live with and I have no insurance and no job so can not afford to go to the doctor unless it is an emergency. I have been having this dark brown clumpy discharge in the past week and have tried all the drug store remedies to balance out my PH and it is not working. I am not do for my period for another two weeks. Is there some cause for this discharge and how can I make it stop.

by ann925, Jun 30, 2009 07:12AM
hello everyone. my case would be familiar for all of you doctors. but i still have question that to be answerd. to beghin with, im only 27 yrs. old. i was only 19 when i give birth for my first child. a year after giving birth my menstration was abnormal, i could have no menstration in 4,6 to 8 months and 1 year. i am merried with a swiss and we was traying to get a baby. i was in doctros for almost 4yrs and still we dont have a baby. we even go trough injectable baby. we did all things that possible to get a baby. but my husband also have a problem hi sperm is weak. please help answer my quetion i am realy concern about my health. my 1st question is: why my mentration is soo abnormal, even now still the same. 2nd: what is wrong with me?? is it something wrong when i give birt form my son? 3rd: what should i do to make my mentraion back into normal. 4th: what should do to make it back into normal?. 5th: could i get still pregnant in normal way? without any help from doctors/medicine?
please any one help me with my problem. looking forward for some answer.
thank you!

by grrrnesss, Jul 02, 2009 10:12PM
So what would cause you to break through the depot shot and start bleeding after an orgasm?

by james_brown, Aug 05, 2009 06:05AM
what's the percentage chance of getting pregnant during cycle day 7 without ejaculating inside the vagina??

by frel82, Aug 09, 2009 06:55AM

Hi Elaine
I am 24 years old and I  was disgnosed with pcos early 2008 and was placed on contraceptive pills and my period beacame regular,after 3months I stoped taking the pills and my period has been regular through out this year up until this month.
I missed my period and went for a test which was negative, I also went for an ultrasound which i do not understand,here is what the results look like.

(The bladder,uterus are normal)now check this out.

OVARIES:Both Ovaried are at the Upper Limits of normal size and have dense stroma,The left ovary contains degenerating remnants of a large Follicle,The right ovary contains tiny peripherally arranged Follicles.

I'm really freaking out now and I need to have an idea before my next visit to the gyna.

Thank u.

by Nieka, Aug 14, 2009 08:45PM
Hi Elaine,

I have an irregular period. I didn't get it in may and june. But in July I started bleeding on the 16th and it started off light pink. It just ended August 10th and it was heavier. Do you think this was my period and it went so long because I didn't get it in may and june? Or is there something else wrong with me?

by Sandra137, Aug 30, 2009 07:35PM
Hi Nieka i would recommend that u should go and check it out......Right now i have same situation and advised to do to my doctor.
Also check this out....womenshealth.gov/menstrual cycle



by pms118, Oct 05, 2009 08:21PM
It's okay neika! It is probably something to do with your birth control & or diet. You really should go talk to a doctor ASAP!


Menstrual Cramp Remedies

by confusedaboutme, Oct 19, 2009 02:05PM
(IN ADVANCE, I APOLOGIZE FOR THE LENGTH OF THIS COMMENT, I'M JUST DESPERATE FOR SOME ANSWERS.)

For some reason I've always been a women's health enigma (albeit unexplained abdominal pain where I’m told I’ve just got cysts & everybody has them; multiple false-positive pregnancy tests; faux PCOS; etc.)…but, THIS truly takes the cake...

Normally, my cycles have ALWAYS been irregular (so its hard to know when what's happening to me is irregular)...that being said, normally (for me) there's quite a bit of time between cycles....often as many as 45-60 days between and they last approx 4-5 days.  Last period was 9/17-25.  Current cycle started 10/3...today is 10/18 and its still going strong, with no signs of tapering off like normal.  Most cycles there is clotting at the beginning, then no clots from midway until the end.  Clots have been present since day 1.  What do I do?  

I don’t trust my doctor-she never listens to me, otherwise I'd call her.  In April she ran a ton of blood tests, and she said I’m perfectly fine on all my levels (then why am I experiencing all these randomly weird female things?!)  Years ago, endometriosis was found during a laparoscopy.  The doc at that time cauterized what he found, and then diagnosed me with PCOS.  I figured it made sense, and he was the Dr.  But then this gal I see now took that diagnosis away in April after the blood tests & that’s fine, its not like I want PCOS, but now I’ve got no explanation behind my female health history.

I'm really not a problem patient, and like I said I'm used to things not being the norm or ideal (its been this way since I was 13 and I'm now 30!), I've just learned to listen to my gut feeling & my gut's telling me that something's very strange about all this.  Please lend some expertise my way, I feel like an alien & I’m losing my mind in the process!  
Thanks in advance.

P.S.
Also, forgot to mention that the readings for H. Pylori were elevated in a blood test done by my allergist 10/2, so I started an antibiotic & Prilosec regiment 10/5.  I wondered if this could aggravate whatever's going on with me, but I started that 2 days after the cycle started & I've been done with that regiment for 3 days now.  
I’m also curious if a recent change in my diet could be causing this.  9/26 SEVERAL new allergies were detected including the following food allergies: wheat, rice, potatoes, corn, soy, yeast, garlic, oranges, tomatoes, clams, shrimp, peas, mustard, peanuts, & walnuts.  It was a challenge to say the least as most of those things are my favorite things to eat!  But I’ve done well since then.  In addition I have an aunt & uncle who are both celiac patients, so as a precaution the doc recommended I adopt a gluten-free lifestyle (no problem with the wheat allergy, but I’m doing even better than that cause I’m allergic to all the gluten alternatives as well!  Side-Note: my stomach feels better than it ever has, and I’ve not got the constipation that’s been a constant since I was a toddler).  I’m wondering if this change in my diet has left me deficient of some important nutrient I’ve overlooked.  I’m taking a super B complex supplement…but could I be low on iron?  Can that cause what I’m going through?  Needless to say I'm still boggled.  Thanks again.


by meseenu, Oct 20, 2009 08:37AM
hi doc,
Presently we(couple) are also facing same problem. we had miscarrage 2 consigutive times that to at 20th week of pregnancy.

can you help us how to over come this.reason for first - cervix opened up giving labour pain.

reason for second - after first mishappen doctor gave "progestron" tablets and also operated (put a stich) so that cervix should hold. but even after that it came down, this time there was no pain.

please, i request you to mail what best can be done to over come this. I really need some advice so that we over come this.

we will be very much great full to you. also what all tests to be done and precauion to be taken for next time.

by meerajasmine, Nov 04, 2009 01:21AM
very detailed n knowledgable...thanks doc

by nessa_m, Nov 19, 2009 05:44PM
thanks i didnt know this much about menstural cycle

by Lissa86, Nov 22, 2009 02:43PM
I'm going to start this post off with a little history then ask my question. I'm 23 and have had 4 pregnancies (that I'm aware of). All of my pregnancies were viable and things were normal resulting in my 4 children. My cycles have been pretty normal until after this last pregnancy which is why I've been keeping track of my cycles and this is what they look like:
Mar 18 to Mar 21; Apr 16 to Apr 19; May 14 to May 18; Jun 22 to Jun 26; Jul 28 to Jul 30; August *NO period*; Sep 1 to Sep 3; Oct 10 to Oct 13.
On Nov. 17th, it had been 37 days since my LMP so I took a home test... the result was positive. I had already been experincing the pregnancy symptoms like I had with my previous pregnancies. On Nov. 19th, I started spotting w/ some back and stomuch cramps. Nov. 20th I had a test done at a clinic... the result was negative and I continued to bleed heavier and with more severe pain. Today, Nov. 22nd, the bleeding is back to spotting and the pain is faint. I took another home test and the result was positive. I've never had this situation occur. Normally I take a test, go to the docter and get the same result.
I'm lost by what is going on. At first after the negative result I thought I may have been miscarrying but now with the second positive result I'm beyond words. Any ideas on what is going on with me? Any suggestions on test to get ran? I need some advice because this is becoming very frustrating for my boyfriend and I. Thanks!

Post a Comment
Post