The cervix pl. The cervix is approximately 4 cm long with a diameter of approximately 3 cm and tends to be described as a cylindrical shape, although the front and back walls of the cervix are contiguous. For example, women in the fertile years of their reproductive cycle tend to have larger cervixes than postmenopausal women; likewise, women who have produced offspring have a larger cervix than those who have not.
In relation to the vagina, the part of the cervix that opens to the uterus is called the internal os and the opening of the cervix in 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 has at least two types of epithelium lining : the endocervical lining is glandular epithelium that lines the endocervix with a single layer of column-shaped cells , while the ectocervical part of the conduit contains squamous epithelium.
These two linings converge at the squamocolumnar junction SCJ. This junction moves throughout a woman's life. Cervical infections with the human papillomavirus HPV can cause changes in the epithelium, which can lead to cancer of the cervix. Cervical cytology tests can detect cervical cancer and its precursors and enable early, successful treatment. HPV vaccines, developed in the early 21st century, reduce the risk of developing cervical cancer by preventing infections from the main cancer-causing strains of HPV.
The cervical canal allows blood to flow from the uterus and through the vagina at menstruation , which occurs in the absence of pregnancy. Several methods of contraception aim to prevent fertilization by blocking this conduit, including cervical caps and cervical diaphragms , preventing sperm from passing through the cervix.
Other approaches include methods that observe cervical mucus, such as the Creighton Model and Billings method. Cervical mucus's consistency changes during menstrual periods , which may signal ovulation.
