Cervix

Cervix
Human cervix
Diagram of the female human reproductive tract
Details
Precursor	Paramesonephric ducts
Artery	Vaginal artery and uterine artery
Identifiers
Latin	cervix uteri
MeSH	D002584
TA98	A09.1.03.010
TA2	3508
FMA	17740
Anatomical terminology [edit on Wikidata]

The cervix (pl.: cervices) or cervix uteri is a dynamic fibromuscular sexual organ of the female reproductive system that connects the vagina with the uterine cavity.^[1] The human female cervix has been documented anatomically since at least the time of Hippocrates, over 2,000 years ago. 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.^[1] The size of the cervix changes throughout a woman's life cycle. 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.^[1]

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.^[1] Between them is a conduit commonly called the cervical canal. The lower part of the cervix, known as the vaginal portion of the cervix (or ectocervix), bulges into the top of the vagina.^{[citation needed]} The endocervix borders the uterus. 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 canal contains squamous epithelium.^[1] Squamous epithelium lines the conduit with multiple layers of cells topped with flat cells. These two linings converge at the squamocolumnar junction (SCJ). This junction moves throughout a woman's life.^[1]

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. Ways to avoid HPV include avoiding heterosexual sex, using penile condoms, and receiving the HPV vaccination. 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.^[2]

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.

During vaginal childbirth, the cervix must flatten and dilate to allow the foetus to move down the birth canal. Midwives and doctors use the extent of cervical dilation to assist decision-making during childbirth.