cervix cervix the cervix or cervix uteri (latin, 'neck of the uterus') is the lower part of the uterus (womb) in the human female reproductive system. the cervix is usually 2 to 3 cm long (~1 inch) and roughly cylindrical in shape, which changes during pregnancy. the narrow, central cervical canal runs along its entire length, connecting the uterine cavity 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 cervix has been documented anatomically since at least the time of hippocrates, over 2,000 years ago. cervixthe human female reproductive system. the cervix is the lower narrower portion of the uterus.detailsprecursormüllerian ductarteryvaginal artery and uterine arteryidentifierslatincervix uterimeshd002584ta98a09.1.03.010ta23508fma17740anatomical terminology 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. cervical mucus is used in several methods of fertility awareness, such as the creighton model and billings method, due to its changes in consistency throughout the menstrual period. during vaginal childbirth, the cervix must flatten and dilate to allow the fetus to progress along the birth canal. midwives and doctors use the extent of the dilation of the cervix to assist decision-making during childbirth. the cervical canal is lined with a single 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 at 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 cervical cancer and its precursors, and enable early successful treatment. ways to avoid hpv include avoiding sex, using condoms, and hpv vaccination. 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. structure diagram of the uterus and part of the vagina. the cervix is the lower part of the uterus situated between the external os (external orifice) and internal os (internal orifice). the cervical canal connects the interior of the vagina and the cavity of the body of uterus. the cervix is part of the female reproductive system. around 2–3 centimetres (0.8–1.2 in) 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 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 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. cervix birth 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 over the course of 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 in such a way 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 natural or normal 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 3 cm (1.2 in) long and 2.5 cm (1 in) wide. blood is supplied to the cervix by the descending branch of the uterine artery and drains into the uterine vein. the pelvic splanchnic nerves, emerging as s2–s3, transmit the sensation of pain from the cervix to the brain. 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 in 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. development as a component of the female reproductive system, the cervix is derived from the two paramesonephric ducts (also called müllerian ducts), which develop around the sixth week of embryogenesis. during development, the outer parts of the two ducts fuse, forming a single urogenital canal that will become the vagina, cervix and uterus. the cervix grows in size at a smaller rate than the body of the uterus, so the relative size of the cervix over time decreases, decreasing from being much larger than the body of the uterus in fetal life, twice as large during childhood, and decreasing to its adult size, smaller than the uterus, after puberty. previously it was thought that during fetal development, the original squamous epithelium of the cervix is derived from the urogenital sinus and the original columnar epithelium is derived from the paramesonephric duct. the point at which these two original epithelia meet is called the original squamocolumnar junction.: 15–16 new studies show, however, that all the cervical as well as large part of the vaginal epithelium are derived from müllerian duct tissue and that phenotypic differences might be due to other causes. histology transformation zone mucosa, when the squamocolumnar junction has a gradual transition. it consists of a mix of stratified squamous epithelium and mucinous glands. h&e stain.histology of endocervix, with mucinous columnar epithelium and mucinous glands. h&e stain. a nulliparous woman's ectocervix showing cervical ectropion, visible as the darker red mucosa surrounding the cervical os. viewed on speculum exam. the endocervical mucosa is about 3 mm (0.12 in) thick and lined with a single layer of columnar mucous cells. it contains numerous tubular mucous glands, which empty viscous alkaline mucus into the lumen. in contrast, the ectocervix is covered with nonkeratinized stratified squamous epithelium, which resembles the squamous epithelium lining the vagina.: 41 the junction between these two types of epithelia is called the squamocolumnar junction.: 408–11 underlying both types of epithelium is a tough layer of collagen. the mucosa of the endocervix is not shed during menstruation. the cervix has more fibrous tissue, including collagen and elastin, than the rest of the uterus. the squamocolumnar junction of the cervix, with abrupt transition: the ectocervix, with its stratified squamous epithelium, is visible on the left. simple columnar epithelium, typical of the endocervix, is visible on the right. a layer of connective tissue is visible under both types of epithelium. transformation zone types:type 1: completely ectocervical (common under hormonal influence).type 2: endocervical component but fully visible (common before puberty).type 3: endocervical component, not fully visible (common after menopause). in prepubertal girls, the functional squamocolumnar junction is present just within the cervical canal.: 411 upon entering puberty, due to hormonal influence, and during pregnancy, the columnar epithelium extends outward over the ectocervix as the cervix everts.: 106 hence, this also causes the squamocolumnar junction to move outwards onto the vaginal portion of the cervix, where it is exposed to the acidic vaginal environment.: 106 : 411 the exposed columnar epithelium can undergo physiological metaplasia and change to tougher metaplastic squamous epithelium in days or weeks,: 25 which is very similar to the original squamous epithelium when mature.: 411 the new squamocolumnar junction is therefore internal to the original squamocolumnar junction, and the zone of unstable epithelium between the two junctions is called the transformation zone of the cervix.: 411 histologically, the transformation zone is generally defined as surface squamous epithelium with surface columnar epithelium or stromal glands/crypts, or both. after menopause, the uterine structures involute and the functional squamocolumnar junction moves into the cervical canal.: 41 nabothian cysts (or nabothian follicles) form in the transformation zone where the lining of metaplastic epithelium has replaced mucous epithelium and caused a strangulation of the outlet of some of the mucous glands.: 410–411 a buildup of mucus in the glands forms nabothian cysts, usually less than about 5 mm (0.20 in) in diameter, which are considered physiological rather than pathological.: 411 both gland openings and nabothian cysts are helpful to identify the transformation zone.: 106 function fertility the cervical canal is a pathway through which sperm enter the uterus after being induced by estradiol after sexual intercourse, and some forms of artificial insemination. some sperm remains in cervical crypts, infoldings of the endocervix, which act as a reservoir, releasing sperm over several hours and maximising the chances of fertilisation. a theory states the cervical and uterine contractions during orgasm draw semen into the uterus. although the "upsuck theory" has been generally accepted for some years, it has been disputed due to lack of evidence, small sample size, and methodological errors. some methods of fertility awareness, such as the creighton model and the billings method involve estimating a woman's periods of fertility and infertility by observing physiological changes in her body. among these changes are several involving the quality of her cervical mucus: the sensation it causes at the vulva, its elasticity (spinnbarkeit), its transparency, and the presence of ferning. cervical mucus several hundred glands in the endocervix produce 20–60 mg of cervical mucus a day, increasing to 600 mg around the time of ovulation. it is viscous because it contains large proteins known as mucins. the viscosity and water content varies during the menstrual cycle; mucus is composed of around 93% water, reaching 98% at midcycle. these changes allow it to function