Endometriosis is a condition where cells from the inner lining of the
uterus are scattered where they do not belong. During each monthly cycle
these groups of endometrial cells respond to the hormones produced by
the ovaries just as they normally would, they swell with blood and bleed
into the surrounding tissue. These areas (the fallopian tubes, uterine
musculature, colon, bladder, and pelvic cavity) however are not meant
to receive this bleeding and become inflamed and quite painful, even disabling.