The cervix is the lower, narrow end of the uterus. It is a 3 to 4 cm cylinder-shaped structure that plays a critical role in female reproduction. The cervix connects the uterus to the vagina.  (Figure 1 & Figure 2) The lining of the cervix has glands that make mucus which changes during the menstrual cycle. Around ovulation the mucus is thin, which allows sperm to pass into the uterus. The uterus connects to the fallopian tubes. For most of the menstrual cycle and during pregnancy the mucus is thick. This helps prevent infections from entering the internal reproductive organs (vagina, uterus, fallopian tubes, and ovaries). During childbirth, the cervix widens and opens (dilates), which allows the baby to pass through the birth canal.
The cervix has 2 parts: The endocervix is the inner part of the cervix (the canal leading into the uterus) with a small opening into the vagina. The ectocervix (or exocervix) is the outer part of the cervix. It is rounded in shape and has tissue that forms a lip that goes into the vagina. Surrounding the cervix there is a fibrous structure called parametrium that helps connect the cervix to other tissues in the pelvis. Cervical Cancer Cervical cancer is a disease in which cancer cells grows in the cells of the cervix.