To understand the differences between a normal and a PCOS menstrual cycle, let’s start with the normal cycle (which will be of interest even to women without PCOS). If you want to directly go to PCOS mentrual cycle, check out this post – The tale of 4 hormones – Irregular Menstrual cycle / PCOS.
To make things a little easier to visualize, let’s watch a play that is directed by the “Brain Boss”. There are 4 main characters in this play.
- Fiona – Follicle-stimulating hormone (FSH)
- Lisa – Luteinizing hormone (LH)
- Elle – Estrogen (Es)
- Polly – Progesterone (P)
So our story starts in the Brain Boss’s Office. He is looking at his calendar and the reports from the managers of different departments. The Brain Boss, after looking at all the reports, decides that it is “time”. He alerts his subordinate department, Hypothalamus. Hypothalamus get things started by sending a messenger to another department – Pituitary gland via GnRH(Gonadotropin Releasing Hormone). Now the pituitary gland, eager to work, sends Fiona (FSH) to the ovaries. Fiona works in the ovaries for sometime. Her job is to develop the follicles found in the ovary. While the follicles mature, they release Elle(estrogen). Elle goes to Brain Boss and happily reports that everything is going according to plan and that it is time he sends Lisa(LH) to release the egg. Elle also goes to the uterus and prepares for the new guest, the egg. Brain Boss sends Lisa, another agent from the pituitary gland, who has to be in peak form to release the egg. As soon as she reaches her peak form (by which time she should have reached the ovaries), the egg escapes the follicles, and travels via the fallopian tube to reach the uterus, kindly prepared by Elle. Now that the follicle is empty, it sends out Polly (Progesterone) to let the pituitary department that their work has been successfully completed and it is time they move to other things. The pituitary department immediately IMs Lisa (LH) and Fiona (FSH) asking them to leave the ovaries. In the mean time, Polly also helps in preparing the uterus while the egg waits for a knight in shining armor,the sperm to come in. Polly’s jobs include – thickening the uterine lining and helping to generate mucus so that the way for the sperm is easy. If the sperm finds its way to the uterus and fertilizes the egg, then the uterus sends a messenger with further instructions (she is knocked up!) to the ovaries. If on the other hand, if sperm never gets to hook up with the egg within 24-48 hours, Polly (progesterone) and Elle (Estrogen) leave the ovaries as well. As they leave, all the preparation they did in the uterus is scrapped (and causes the bloody hell that is menstruation) and the cycle starts all over again!
[The above “story” is a mnemonic for the actual events that happen in our body during the normal menstrual cycle. For the actual biological sequence see the list below the second picture]
Phases of the regular cycle
The following chart depicts what happens with the different players (hormones, ovaries, uterus and basal body temperature) during different phases of the cycle.
Now let us see how these events are brought about.
Event of a normal menstrual cycle and the hormones responsible for each stage
The following chart shows the sequence of events during the normal menstrual cycle. The different hormones are colored different and you can match them with the above picture to see what their level of presence is, in each stage.
- Orange GnRH
- Blue Estrogen
- Red Leutinizing hormone (LH)
- Green Progesterone (Prog)
- Hypothalamus releases Gonadotropin-releasing hormone (GnRH)
- GnRH causes the pituitary gland to produce FSH. FSH reaches the ovaries via the blood stream. FSH causes the follicles to mature. Follicles are little balloon like sacs filled with cells and fluid and hold an egg. Each follicle contains one single egg.
- Maturing follicles produce estrogen. Estrogen signals the brain, which slows down the FSH production and starts LH production in pituitary glands.
- Estrogen also prepares the uterus for ovulation by thickening the blood vessels lining the uterus.
- Estrogen production boosts LH.
- LH surges and causes ovulation. The egg escapes, travels via the fallopian tube and goes to the Uterus.
- The empty follicle from which the egg was released is called as Corpus Luteum or yellow body. The Corpus Luteum produces Progesterone. Progesterone signals the brain to stop producing LH.
- Progesterone also prepares the uterus by thickening the uterus lining and also producing mucus to ease the passage of the sperm. The egg sits and waits for 24-48 hrs.
- If you get pregnant, the hCG hormone is produced by the developing embryo. This hormone signals the Corpus Luteum to keep making Progesterone and Estrogen. If you don’t get pregnant, the corpus luteum disintegrates (called as Corpus Albican) and stops producing Progesterone and Estrogen. The low levels of Progesterone and Estrogen causes menstruation to occur.
- The cycle starts all over again.
In the next post I will describe what happens to the cycle if you have PCOS (Update: you can find that post here – The tale of 4 hormones – Irregular Menstrual cycle / PCOS). Whether you have PCOS or not, it is always good to know about your body. Hormones are powerful chemicals released by a cell in one part of the body, to send out messages that affect cells in other parts of the organism. Getting a better idea of what role they play and how they work is the first step toward understanding our menstrual cycle and taking control of our fertility.
If you see any inaccuracies or confusing parts, please drop me a line, I will be happy to correct the problem or elaborate. Thanks!