Menopause - What happens every month

Menopause

What happens every month

Your menstrual cycle usually lasts about 28 days. But it can be as short as 20 days or as long as 36 days.

It's controlled by your

hormones
Hormones are chemicals that are made in certain parts of the body. They travel through the bloodstream and have an effect on other parts of the body. For example, the female sex hormone estrogen is made in a woman's ovaries. Estrogen has many different effects on a woman's body. It makes the breasts grow at puberty and helps control periods. It is also needed to get pregnant.

hormones and it has three stages.

Source:
Guyton AC, and Hall JE.
Female physiology before pregnancy and the female hormones.
In: Textbook of medical physiology. WB Saunders, Philadelphia, U.S.A.; 2000.

Early cycle

Your cycle begins on the first day of your period. Your hormone levels are low at this time.
In the first few days, part of your brain starts making a hormone called gonadotropin-releasing hormone (GnRH).
GnRH tells another part of your brain to make two more hormones. They're called luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
They travel in your bloodstream to your

ovaries
Women have two ovaries, one on each side of their womb. They are small glands that store eggs. Inside the ovaries are millions of pre-eggs, called follicles. Some of these grow into eggs.

ovaries. Here, the hormones tell eggs to start growing.
The growing eggs make the hormone estrogen.
Estrogen makes the lining of your womb (endometrium) start to get thicker.
One egg grows faster than the others. The rest shrivel up.

Mid cycle

In the middle of your menstrual cycle, your levels of luteinizing hormone (LH) rise sharply.
This helps the growing egg come out of your ovary. This is called ovulation.
The egg goes into one of your

fallopian tubes
Fallopian tubes are the two tubes that come out of the top of a woman's womb. They carry eggs from the ovaries to the womb.

fallopian tubes. The tube's tiny hairs push the egg along, toward your womb.

Late cycle

Your body gets ready for pregnancy.
Your ovaries keep making estrogen and start to make lots of progesterone.
Progesterone makes the lining of your womb even thicker, so it's ready for a fertilized egg.
If a fertilized egg arrives, it might stick to your womb lining and start to grow. This is how pregnancy starts.

Two things can happen.

These graphs show how the levels of different hormones change during your monthly cycle.

You get pregnant. Your hormone levels stay high to keep your pregnancy going.
You don't get pregnant. Your hormone levels start to drop. Without hormones, the lining of your womb breaks down, pulls away and flows out of your vagina. This is when you have your period. And your menstrual cycle starts all over again.

Sources for the information on this page:

Guyton AC, and Hall JE.Female physiology before pregnancy and the female hormones.In: Textbook of medical physiology. WB Saunders, Philadelphia, U.S.A.; 2000.

This information was last updated on Sep 11, 2009

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