FACT: The uterus is made up of the fallopian tubes, the body of the uterus (womb) and the cervix. It's only about three inches long, but when pregnant the uterus can expand to hundreds of times its normal volume. There are three layers in the uterus. The inner and most active layer is called the endometrium. The middle layer is called the myometrium, the muscular layer is responsible for menstrual cramps and contractions during labor. The outside layer is called the epimetrium, which is a thin layer of protective tissue.