What causes Endometriosis?

The exact cause is not known. It is thought that some cells from the lining of the uterus (the endometrium) get outside the uterus into the pelvic area. They probably get there by spilling backwards along the fallopian tubes when you have a period. Although 70% of women do menstruate through the tubes, only 10% develop the disease so this is only a partial explanation of why it develops. The majority of women have a natural defence, killing the cells of the menstrual fluid before they implant. Women who develop endometriosis have reduced ability to kill these cells or a reduced ability to stop their growth after they implant in the pelvis.

Endometrial cells can also grow in the wall of the uterus trapping blood in the muscle of the womb causing severe pain. This is called Adnomyosis or Endometriosis Interni.

The endometrial cells continue to survive next to the uterus, ovary, bladder, bowel, or fallopian tube. The cells respond to the female hormone oestrogen, just like the lining of the uterus does each month. Throughout each month the cells multiply and swell, and then break down as if ready to be shed at the time of your period. However, because they are trapped inside the pelvic area, they cannot escape. They form patches of tissue called endometriosis.

Patches of endometriosis tend to be 'sticky' and may join organs to each other. The medical term for this is adhesions. For example, the bladder or bowel may 'stick' to the uterus. Large patches of endometriosis may form into cysts which bleed each month when you have a period. The cysts can fill with dark blood often called 'chocolate cysts'.

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