Cervix

About the Cervix

The cervix is the lower, narrow, cylindrical part of the uterus that projects into the upper vagina. A canal runs through its center, connecting the vaginal opening, the external os, with the uterine cavity, through the internal os. The part facing the vagina is covered by squamous epithelium, while the canal is lined by mucus secreting columnar epithelium, and the area where these meet, the transformation zone, is where most cervical cancers arise. Cervical mucus changes throughout the menstrual cycle, becoming thin and stretchy around ovulation to allow sperm to pass and thicker at other times, acting as a barrier against infection. During pregnancy the cervix stays firm and closed to hold the pregnancy, and during labor it softens, thins, and dilates to allow the baby to pass. Persistent infection with high risk types of human papillomavirus causes almost all cervical cancers, and cervical screening and HPV vaccination have substantially reduced cervical cancer rates in many countries.