Cervix

The cervix (Latin: neck) or cervix uteri is the lower part of the uterus. In a non-pregnant woman, the cervix is usually between 2 and 3 cm long and roughly cylindrical in shape. The narrow, central cervical canal runs along its entire length, connecting the cavity of the body of the uterus and the lumen of the vagina. The opening into the uterus is called the internal os and the opening into the vagina is called the external os. The lower part of the cervix, known as the vaginal portion of the cervix (or ectocervix), bulges into the top of the vagina.

The cervical canal is a passage through which sperm must travel to fertilize an egg cell after sexual intercourse. Several methods of contraception, including cervical caps and cervical diaphragms aim to block or prevent the passage of sperm through the cervical canal. During vaginal childbirth, the cervix must flatten and dilate to allow the fetus to progress along the birth canal.

The endocervical canal is lined with a layer of column-shaped cells, while the ectocervix is covered with multiple layers of cells topped with flat cells. The two types of epithelia meet the squamocolumnar junction. Infection with the human papillomavirus (HPV) can cause changes in the epithelium, which can lead to cancer of the cervix. Cervical cytology tests can often detect precursors of cervical cancer and enable early successful treatment. Ways to avoid HPV include avoiding sex, using condoms, and HPV vaccination. The HPV vaccines, developed in the early 21st century, reduce the risk of cervical cancer by preventing infections from the main cancer-causing strains of HPV.