Cervix

The cervix ( : cervices) or uterine cervix ( ) is a dynamic fibromuscular sexual organ of the female reproductive system that connects the vagina with the uterine cavity. The human female cervix has been documented anatomically since at least the time of Hippocrates, over 2,000 years ago. The cervix is approximately long with a diameter of approximately and tends to be described as a cylindrical shape, although the front and back walls of the cervix are contiguous. 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. 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. 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 cervix ( : cervices) or uterine cervix ( ) is a dynamic fibromuscular sexual organ of the female reproductive system that connects the vagina with the uterine cavity. The human female cervix has been documented anatomically since at least the time of Hippocrates, over 2,000 years ago. The cervix is approximately long with a diameter of approximately and tends to be described as a cylindrical shape, although the front and back walls of the cervix are contiguous. 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. 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. 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 epithelium that lines the endocervix with a single layer of column-shaped cells; while the ectocervical part of the conduit contains squamous epithelium. 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. The cervix is the organ that allows epithelia to flow from a female's uterus and out through her vagina at menstruation. Menstruation 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 ovulation 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. and part of the vagina. The cervix is the lower part of the uterus situated between the external os (external orifice) and the internal os (internal orifice). The cervical canal connects the interior of the vagina and the cavity of the body of the uterus.|alt=Diagram of the uterus and part of the vagina. The cervix is part of the female reproductive system. Around in length, it is the lower, narrower part of the uterus, continuous above with the broader upper part—or body—of the uterus. The lower end of the cervix bulges through the anterior wall of the vagina, and is referred to as the vaginal portion of the cervix (or ectocervix), while the rest of the cervix above the vagina is called the supravaginal portion of cervix. A central canal, known as the cervical canal, runs along its length and connects the cavity of the body of the uterus with the lumen of the vagina. The openings are known as the internal os and external orifice of the uterus (or external os), respectively. The mucosa lining the cervical canal is known as the endocervix, and the mucosa covering the ectocervix is known as the exocervix. The cervix has an inner mucosal layer, a thick layer of smooth muscle, and posteriorly the supravaginal portion has a serosal covering consisting of connective tissue and overlying peritoneum. |A normal cervix of an adult viewed through a vagina using a bivalved vaginal speculum. The functional squamocolumnar junction surrounds the external os and is visible as the irregular demarcation between the lighter and darker shades of pink mucosa. In front of the upper part of the cervix lies the bladder, separated from it by cellular connective tissue known as parametrium, which also extends over the sides of the cervix. To the rear, the supravaginal cervix is covered by peritoneum, which runs onto the back of the vaginal wall and then turns upwards and onto the rectum, forming the recto-uterine pouch. The cervix is more tightly connected to surrounding structures than the rest of the uterus. The cervical canal varies greatly in length and width between women or throughout a woman's life, and it can measure 8 mm (0.3 inch) at its widest diameter in premenopausal adults. It is wider in the middle and narrower at each end. The anterior and posterior walls of the canal each have a vertical fold, from which ridges run diagonally upwards and laterally. These are known as palmate folds, due to their resemblance to a palm leaf. The anterior and posterior ridges are arranged so that they interlock with each other and close the canal. They are often effaced after pregnancy. The ectocervix (also known as the vaginal portion of the cervix) has a convex, elliptical shape and projects into the cervix between the anterior and posterior vaginal fornices. On the rounded part of the ectocervix is a small, depressed external opening, connecting the cervix with the vagina. The size and shape of the ectocervix and the external opening (external os) can vary according to age, hormonal state, and whether childbirth has taken place. In women who have not had a vaginal delivery, the external opening is small and circular, and in women who have had a vaginal delivery, it is slit-like. On average, the ectocervix is long and wide. Blood is supplied to the cervix by the descending branch of the uterine artery and drains into the uterine vein. Sensory innervation of the cervix is conveyed through both visceral and somatic pathways. Visceral pain from the supravaginal portion of the cervix is transmitted via afferent fibers that travel with sympathetic nerves to spinal cord levels T10-L1 through the inferior hypogastric and uterovaginal plexuses. The vaginal portion of the cervix receives somatic sensory innervation via branches of the pudendal nerve (S2-S4). Parasympathetic fibers arising from the pelvic splanchnic nerves (S2-S4) contribute autonomic input via the inferior hypogastric plexus. These nerves travel along the uterosacral ligaments, which pass from the uterus to the anterior sacrum. Three channels facilitate lymphatic drainage from the cervix. The anterior and lateral cervix drains to nodes along the uterine arteries, travelling along the cardinal ligaments at the base of the broad ligament to the external iliac lymph nodes and ultimately the paraaortic lymph nodes. The posterior and lateral cervix drains along the uterine arteries to the internal iliac lymph nodes and ultimately the paraaortic lymph nodes, and the posterior section of the cervix drains to the obturator and presacral lymph nodes. However, there are variations as lymphatic drainage from the cervix travels to different sets of pelvic nodes in some people. This has implications for scanning nodes for involvement in cervical cancer. After menstruation and directly under the influence of estrogen, the cervix undergoes a series of changes in position and texture. During most of the menstrual cycle, the cervix remains firm and is positioned low and closed. However, as ovulation approaches, the cervix becomes softer and rises to open in response to the higher levels of estrogen present. These changes are also accompanied by changes in cervical mucus, described below.

Clinical significance

Cancer

In 2008, cervical cancer was the third-most common cancer in women worldwide, with rates varying geographically from less than one to more than 50 cases per 100,000 women. It is a leading cause of cancer-related death in poor countries, where delayed diagnosis leading to poor outcomes is common. The introduction of routine screening has resulted in fewer cases of (and deaths from) cervical cancer; this has mainly taken place in developed countries. Most developing countries have limited or no screening, and 85% of the global burden occurs there. Cervical cancer nearly always involves human papillomavirus (HPV) infection. HPV is a virus with numerous strains, several of which predispose to precancerous changes in the cervical epithelium, particularly in the transformation zone, which is the most common area for cervical cancer to start. HPV vaccines, such as Gardasil and Cervarix, reduce the incidence of cervical cancer, by inoculating against the viral strains involved in cancer development. Potentially precancerous changes in the cervix can be detected by cervical screening, using methods including a Pap smear (also called a cervical smear), in which epithelial cells are scraped from the surface of the cervix and examined under a microscope. The colposcope, an instrument used to see a magnified view of the cervix, was invented in 1925. The Pap smear was developed by Georgios Papanikolaou in 1928. A LEEP procedure using a heated loop of platinum to excise a patch of cervical tissue was developed by Aurel Babes in 1927. In some parts of the developed world, including the UK, the Pap test has been superseded with liquid-based cytology. An inexpensive, cost-effective, and practical alternative in poorer countries is visual inspection with acetic acid (VIA). Instituting and sustaining cytology-based programs in these regions can be difficult, due to the need for trained personnel, equipment, and facilities and difficulties in follow-up. With VIA, results and treatment can be available on the same day. As a screening test, VIA is comparable to cervical cytology in accurately identifying precancerous lesions. A result of dysplasia is usually further investigated, such as by taking a cone biopsy, which may also remove the cancerous lesion. Cervical intraepithelial neoplasia is a possible result of the biopsy and represents dysplastic changes that may eventually progress to invasive cancer. Most cases of cervical cancer are detected in this way, without having caused any symptoms. When symptoms occur, they may include vaginal bleeding, discharge, or discomfort.

Inflammation

Inflammation of the cervix is referred to as cervicitis. This inflammation may be of the endocervix or ectocervix. When associated with the endocervix, it is associated with a mucous vaginal discharge and sexually transmitted infections such as chlamydia and gonorrhoea. As many as half of pregnant women having a gonorrheal infection of the cervix are asymptomatic. Other causes include overgrowth of the commensal flora of the vagina. When associated with the ectocervix, inflammation may be caused by the herpes simplex virus. Inflammation is often investigated through directly visualising the cervix using a speculum, which may appear whiteish due to exudate, and by taking a Pap smear and examining for causal bacteria. Special tests may be used to identify particular bacteria. If the inflammation is due to a bacterium, then antibiotics may be given as treatment.

Anatomical abnormalities

Cervical stenosis is an abnormally narrow cervical canal, typically associated with trauma caused by removal of tissue for investigation or treatment of cancer, or cervical cancer itself. Diethylstilbestrol, used from 1938 to 1971 to prevent preterm labour and miscarriage, is also strongly associated with the development of cervical stenosis and other abnormalities in the daughters of the exposed women. Other abnormalities include: vaginal adenosis, in which the squamous epithelium of the ectocervix becomes columnar; cancers such as clear cell adenocarcinomas; cervical ridges and hoods; and development of a cockscomb cervix appearance, which is the condition wherein, as the name suggests, the cervix of the uterus is shaped like a cockscomb. About one-third of women born to diethylstilbestrol-treated mothers (i.e., in-utero exposure) develop a cockscomb cervix. Enlarged folds or ridges of cervical stroma (fibrous tissues) and epithelium constitute a cockscomb cervix. Similarly, cockscomb polyps lining the cervix are usually considered or grouped into the same overarching description. It is in and of itself considered a benign abnormality; its presence, however, is usually indicative of DES exposure, and as such, women who experience these abnormalities should be aware of their increased risk of associated pathologies. Cervical agenesis is a rare congenital condition in which the cervix completely fails to develop, often associated with the concurrent failure of the vagina to develop. Other congenital cervical abnormalities exist, often associated with abnormalities of the vagina and uterus. The cervix may be duplicated in situations such as bicornuate uterus and uterine didelphys. Cervical polyps, which are benign overgrowths of endocervical tissue, if present, may cause bleeding, or a benign overgrowth may be present in the cervical canal. Cervical ectropion refers to the horizontal overgrowth of the endocervical columnar lining in a one-cell-thick layer over the ectocervix.

Animals

Female marsupials have paired uteri and cervices. Most eutherian (placental) mammal species have a single cervix and a single, bipartite or bicornuate uterus. Lagomorphs, rodents, aardvarks, and hyraxes have a duplex uterus and two cervices. Lagomorphs and rodents share many morphological characteristics and are grouped in the clade Glires. Anteaters of the family Myrmecophagidae are unusual in that they lack a defined cervix; they are thought to have lost the characteristic, rather than other mammals developing a cervix on more than one lineage. In domestic pigs, the cervix contains a series of five interdigitating pads that hold the boar's corkscrew-shaped penis during copulation.

Etymology and pronunciation

The word cervix ( ) came to English from Latin , which means "neck". Like its English translation, the Latin word can refer not only to the neck [of the body], but also to an analogous narrowed part of an object. Thus, the term (literally "neck of the uterus") is used in Latin to refer to the uterine cervix, but in English, the word cervix used alone usually refers to it. The first attested use of the word in English to refer to the cervix of the uterus was in 1702. The adjective cervical may refer either to the neck (as in cervical vertebrae or cervical lymph nodes) or to the uterine cervix (as in cervical cap or cervical cancer). The Latin word was in turn used to translate the Greek word ( ), "neck". The cervix was documented in anatomical literature in at least the time of Hippocrates; cervical cancer was first described more than 2,000 years ago, with descriptions provided by both Hippocrates and Aretaeus. Greek writers usually used the term ( ) to refer to the cervical canal; however, there was some variation in the sense of these two words.

Text derived from https://en.wikipedia.org/w/index.php?oldid=1377313333 under CC BY-SA 4.0; modifications have been made.