Endometriosis - What happens every month

Endometriosis

What happens every month

Your menstrual cycle lasts about 28 days but it can be shorter or longer. 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. The cycle 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, USA; 2000.

Early cycle

Your cycle begins on the first day of your period. At this time, you have low levels of hormones.
In the first few days, part of your brain starts making a hormone called gonadotropin-releasing hormone (or GnRH for short).
GnRH tells another part of the brain to produce two more hormones. They're called luteinizing hormone (LH) and follicle-stimulating hormone (FSH).
LH and FSH 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 some eggs to start growing.
The growing eggs make two more hormones called estrogen and progesterone.
One egg grows faster than the others. This egg keeps growing and the others shrivel up. This tends to happen in alternate ovaries each month.

Mid cycle

In the middle of your menstrual cycle, there's a big increase in the amount of luteinizing hormone (LH) in your body.
This helps the growing egg move out of your ovary into 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 tube. This is called ovulation.
Tiny hairs in the tube push the egg along the tube, toward your womb.

Late cycle

At the end of your cycle, your body prepares for pregnancy.
Your ovary starts to make large amounts of a hormone called progesterone.
This hormone makes the lining of your womb thicker, ready for a fertilized egg to arrive. If an egg arrives, it joins to the lining of your womb. This lining is called the endometrium.

After your cycle

Two things can happen at the end of your cycle:

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

You get pregnant. The levels of hormones in your body stay high to continue your pregnancy.
You don't get pregnant. Hormone levels start to drop. Without hormones, the lining of your womb begins to break down and fall toward your vagina. This is when you have your period. When your period has finished, hormone levels start to rise and the cycle starts 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, USA; 2000.

This information was last updated on Nov 06, 2008

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