What Is Endometriosis?

Endometriosis is a disorder in which bits of tissue from the inner lining of the uterus (the endometrium) grow inside a woman’s body, outside of the uterus. The uterus is a hollow organ within a woman’s abdomen where a fertilized egg implants and where a developing baby is nourished and grows.

These misplaced bits of endometrial tissue can cause pain and irregular bleeding, and can affect a woman’s ability to become pregnant.

Each month, in a normal menstrual cycle:

  • The ovaries (the organs where egg cells develop) produce hormones (the body’s chemical messengers) that stimulate the cells of the uterine lining – the endometrial cells – to multiply and prepare for a fertilized egg. These cells swell and thicken.
  • If a pregnancy does not occur, this excess tissue is shed from the uterus and discharged from the body.
  • This discharge of tissue is a woman’s menstrual period.

In endometriosis:

  • Patches of misplaced endometrial tissue implant themselves on organs outside of the uterus, such as the ovaries, fallopian tubes rectum, and bladder.
  • These cells also respond to the ovaries’ hormonal signals by swelling and thickening.
  • However, these cells are unable to separate themselves and shed from the tissue to which they have adhered. They sometimes bleed a little and then heal.
  • This happens repeatedly each month, and the ongoing process can cause scarring. It also can create adhesions, which are web-like tissues that can bind pelvic organs together.

How Common Is Endometriosis?

Endometriosis sometimes produces no symptoms, and many women are unaware that they have the condition. Therefore, the true incidence is hard to determine. But many experts believe it affects between 5 and 15 percent of all women of reproductive age.

Where In The Body Does Endometriosis Occur?

Endometrial tissue can grow anywhere in the abdomen, including:

  • Ovaries
  • Fallopian tubes
  • Outer surface of the uterus
  • Bladder
  • Rectum

Less commonly, endometrial tissue may adhere to:

  • Outer surfaces of the small and large intestines
  • Ureters (tubes leading to from the kidneys to the bladder)
  • Vagina
  • Surgical scars in the abdomen
  • Lining of the chest cavity
  • Other areas outside the abdomen, such as the lung or thigh (this is rare)

Need To Know:

Endometrial cells that adhere to an ovary can cause a cyst, known as an endometrioma, to develop. These can grow to the size of an egg or even larger, and they are usually very painful. The fluid inside the cyst contains blood and may in time become thick and brown; for this reason, the cysts are known as “chocolate cysts.” In some cases they may rupture or leak, causing severe abdominal pain.

Need To Know:

Endometrial tissue can attach to the lower portion of the intestines and the rectum, which can cause bowel pain during a woman’s menstrual period. In some cases, it can cause rectal bleeding as well.

Facts About Endometrioisis

  • Endometriosis is fairly common, and there is no other condition in medicine quite like it.
  • Estimates vary widely, but endometriosis is believed to affect about 5 to 15 percent of women of reproductive age.
  • Endometriosis is most common among women who are in their 30s and 40s.
  • Endometriosis begins only after menstruation begins; the disease has never been found in young women who have not yet begun to menstruate.
  • Endometriosis is no longer active in women who have reached menopause.
  • Little is known about why some women develop endometriosis and others do not.
  • Endometriosis is more common among Caucasian women.
  • Endometriosis appears to run in families.


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