The endometrium (en-doe-MEE-tree-um) is a membrane that lines the surface of the uterus. Endometriosis (en-doe-mee-tree-O-sis) occurs when fragments of endometrial tissue develop outside the uterus, such as in or on the ovaries, the fallopian tubes, or other places in the abdominal cavity. Less commonly, endometriosis may occur on the bowel or bladder. These fragments respond to the hormonal changes of each menstrual cycle by growing, then being shed as blood, the same way as the endometrial membrane does in the uterus. The blood and other material can irritate or damage adjacent tissue, and scars may form. Endometriosis can even lead to infertility. Symptoms of endometriosis include chronic pain in the lower abdomen, especially during periods, pain during or after sexual intercourse, painful bowel movements, and irregular menstrual cycles. Endometriosis may also exist without any symptoms. Treatment options vary from medication to radical surgery, and depend on the extent of the condition. Oral contraceptives can lower your risk of developing endometriosis, due to the progesterone (pro-GESS-ter-own) they contain. For more information on endometriosis, contact a health care provider.