Cervix

The cervix (pl.: cervices) or uterine cervix (Latin: 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 (1.6 in) long with a diameter of approximately 3 cm (1.2 in) 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 female's life cycle. For example, females in the fertile years of their reproductive cycle tend to have larger cervixes than postmenopausal females; likewise, females 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 into the uterus is called the internal os while the opening of the cervix into the vagina is called the external os.^[1] Between those extremes is the 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. The endocervix borders the uterus. The cervical conduit has at least two types of epithelium (lining): the endocervical lining is glandular epithelia that lines the endocervix with a single layer of column-shaped cells; while the ectocervical part of the conduit contains squamous epithelium.^[1] Squamous epithelia line the conduit with multiple layers of cells topped with flat cells. These two linings converge at the squamocolumnar junction (SCJ). This junction changes location dynamically throughout a female's life.^[1]The cervix is the organ that allows epithelia to flow from a female's uterus and out through her vagina at menstruation. Mensturation releases epithelia from a female’s uterus with every period of her fertile years, unless pregnancy occurs.

Several methods of contraception aim to prevent fertilization by blocking the conduit, including cervical caps and cervical diaphragms, preventing the passage of sperm 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 progress along the birth canal. Midwives and doctors use the extent of cervical dilation to assist decision-making during childbirth.

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 to 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]