The cervix is not a separate organ, but is a highly modified portion of the uterus. During most of the menstrual cycle, the cervix serves as a barrier between the vagina and the uterus, impeding entry of sperm and microorganisms. During pregnancy, its heavy fibrous coat and secreted mucus plug help to retain the developing fetus. In the cervix, the smooth muscle of the myometrium is partially replaced by dense irregular connective tissue. HA30 and HA31 show the cervical glands. At low magnification (HA30), you can tell that these glands are very different from those in the fundus and body of the uterus. Secretions (arrows) can be seen between the branched glands.