Endometrium is the tissue that makes up the uterine lining. Endometriosis is a condition in which this tissue is present on other organs inside your body. It is usually found on the ovaries, fallopian tubes, the surface of the uterus, and bladder wall. Displaced tissue continues to act as it normally would – thickens, breaks down, and bleeds with each menstrual cycle. As this tissue has no way to exit your body, it becomes trapped and the surrounding tissues can become irritated developing scar tissues and adhesions.
Retrograde menstruation is one of the causes of endometriosis. Menstrual blood containing endometrial cells flows back through fallopian tubes and into the pelvic cavity. These displaced endometrial cells are deposited in unusual locations. These lesions are commonly found in the ovaries, fallopian tubes, lining of pelvic cavity, and cervix. The displaced tissue can also be found on lining of the bladder and the bowel wall.