The cervix is the lower part of the uterus that opens into the vagina. It is also called the neck of the uterus.

The endometrium is the mucous membrane that lines the inside of the uterus (womb). The endometrium changes throughout the menstrual cycle. It becomes thick and rich with blood vessels to prepare for pregnancy. If the woman does not get pregnant, part of the endometrium is shed, causing menstrual bleeding.