Editing Cervix (section)

== Structure ==
[[File:Gray1167.svg|right|thumbnail|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 the internal os (internal orifice). The [[cervical canal]] connects the interior of the vagina and the cavity of the body of uterus.|alt=Diagram of the uterus and part of the vagina.]]

The cervix is part of the [[female reproductive system]]. Around {{convert|2–3|cm|in|1}} in length,<ref name=KURMAN1994/> it is the lower, narrower part of the uterus continuous above with the broader upper part—or body—of the uterus.<ref name=Gray38/> 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]].<ref name=Gray38/> A central canal, known as the [[Canal of the cervix|cervical canal]], runs along its length and connects the [[cavity of the body of the uterus]] with the lumen of the vagina.<ref name=Gray38/> The openings are known as the [[internal os]] and [[external orifice of the uterus]] (or external os), respectively.<ref name=Gray38/> The mucosa lining the cervical canal is known as the [[endocervix]],<ref name=GRAYS2005>{{cite book | vauthors = Drake RL, Vogl W, Mitchell AW  |others=Illustrations by Richardson P, Tibbitts R |title=Gray's Anatomy for Students |year=2005 |publisher= Elsevier/Churchill Livingstone |location= Philadelphia, PA |isbn= 978-0-8089-2306-0  |pages= 415, 423}}</ref> and the mucosa covering the ectocervix is known as the exocervix.<ref>{{cite book |vauthors = Ovalle WK, Nahirney PC |others=Illustrations by Frank H. Netter, contributing illustrators, Joe Chovan, et al. |title=Netter's Essential Histology |date=2013 |chapter= Female Reproductive System |publisher= Elsevier/Saunders |location= Philadelphia, PA |isbn=978-1-4557-0631-0 |page=416 |edition=2nd }}</ref> 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]].<ref name=Gray38/>

[[File:Cervix uteri, breastfeeding woman after 2 births.jpg|thumbnail|alt=A adult woman's cervix viewed through vagina using a [[Speculum (medical)#Vaginal|vaginal speculum]]|A normal cervix of an adult viewed through vagina using a [[Speculum (medical)#Vaginal|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 [[Mucous membrane|mucosa]].]]

[[File:Cervix birth.png|thumb|Cervix before (left) and after vaginal birth (right)]]

In front of the upper part of the cervix lies the [[Urinary bladder|bladder]], separated from it by cellular connective tissue known as [[parametrium]], which also extends over the sides of the cervix.<ref name=Gray38>{{Cite book | vauthors = Gray H |author-link=Henry Gray | veditors = Williams PL |title=Gray's Anatomy |edition=38th |isbn=0-443-04560-7 |year=1995 |publisher=[[Churchill Livingstone]] |pages=1870–73|title-link=Gray's Anatomy }}</ref> 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]].<ref name=Gray38/> The cervix is more tightly connected to surrounding structures than the rest of the uterus.<ref name="Gardner69">{{cite book | vauthors = Gardner E, Gray DJ, O'Rahilly R |title= Anatomy: A Regional Study of Human Structure |publisher= W.B. Saunders |location= Philadelphia, PA |date=1969 |orig-year=1960 |edition= 3rd |pages= 495–98}}</ref>

The cervical canal varies greatly in length and width between women or throughout a woman's life,<ref name=KURMAN1994 /> and it can measure 8&nbsp;mm (0.3&nbsp;inch) at its widest diameter in [[Premenopause|premenopausal]] adults.<ref name=Blaustein2002/> 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 they interlock with each other and close the canal. They are often effaced after pregnancy.<ref name="Gardner69"/><!-- cites previous five sentences -->

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 fornix|vaginal fornices]]. On the rounded part of the ectocervix is a small, depressed [[external orifice of the uterus|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.<ref name=Blaustein2002>{{cite book|title=Blaustein's Pathology of the Female Genital Tract |edition=5th |page=207 |publisher=Springer |year=2002 |veditors = Kurman RJ }}</ref> On average, the ectocervix is {{convert|3|cm|in|abbr=on}} long and {{convert|2.5|cm|in|sigfig=1|abbr=on}} wide.<ref name=KURMAN1994 />

Blood is supplied to the cervix by the descending branch of the [[uterine artery]]<ref name=DAFTARY2011>{{cite book| vauthors = Daftary SN, Chakravari S |title=Manual of Obstretics, 3/e|year=2011|isbn=978-81-312-2556-1|publisher=Elsevier|pages=1–16}}</ref> and drains into the [[uterine vein]].<ref name=ELLIS2011 /> The [[pelvic splanchnic nerves]], emerging as [[Sacral spinal nerve 2|S2]]–[[Sacral spinal nerve 3|S3]], transmit the sensation of pain from the cervix to the brain.<ref name= GRAYS2005 /> These nerves travel along the [[uterosacral ligament]]s, which pass from the uterus to the anterior [[sacrum]].<ref name="DAFTARY2011"/>

Three channels facilitate [[Lymphatic system|lymphatic drainage]] from the cervix.<ref name=SINGER2005>{{cite book | vauthors = Mould TA, Chow C | chapter = The Vascular, Neural and Lymphatic Anatomy of the Cervix | veditors = Jordan JA, Singer A |title=The Cervix |url=https://archive.org/details/cervixndedition00jord |url-access=limited |date=2005|publisher= Blackwell Publishing |location= Oxford, United Kingdom |pages=[https://archive.org/details/cervixndedition00jord/page/n55 41]–47 |isbn= 9781405131377 |edition=2nd}}</ref> The anterior and lateral cervix drains to [[lymph node|nodes]] along the uterine arteries, travelling along the [[cardinal ligament]]s at the base of the [[broad ligament]] to the [[external iliac lymph nodes]] and ultimately the [[paraaortic lymph node]]s. 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 node]]s.<ref name=KURMAN1994>{{cite book|veditors = Kurman RJ|title=Blaustein's Pathology of the Female Genital Tract|year=1994|publisher=Springer New York|location=New York, NY|isbn=978-1-4757-3889-6|pages=185–201|edition=4th}}</ref><ref name=ELLIS2011>{{cite journal| vauthors = Ellis H |title=Anatomy of the uterus |journal=Anaesthesia & Intensive Care Medicine |year=2011|volume=12|issue=3|pages=99–101|doi=10.1016/j.mpaic.2010.11.005}}</ref><ref name=SINGER2005 /> 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.<ref name=SINGER2005/>

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.<ref name=Weschler>{{cite book | vauthors = Weschler T |title=Taking charge of your fertility: the definitive guide to natural birth control, pregnancy achievement, and reproductive health |year=2006 |publisher=Collins |location=New York, NY |isbn=978-0-06-088190-0 |pages=[https://archive.org/details/takingchargeofy000wesc/page/59 59, 64] |edition=Revised |url=https://archive.org/details/takingchargeofy000wesc/page/59 }}</ref> These changes are also accompanied by changes in cervical mucus,<ref name=CERVIX2006/> described below.

=== Development ===
As a component of the female [[Human reproductive system|reproductive system]], the cervix is derived from the two [[paramesonephric duct]]s (also called Müllerian ducts), which develop around the sixth week of [[human embryogenesis|embryogenesis]]. During development, the outer parts of the two ducts fuse, forming a single [[urogenital]] canal that will become the [[vagina]], cervix and [[uterus]].<ref>{{cite book| vauthors = Schoenwolf GC, Bleyl SB, Brauer PR, Francis-West PH |title=Larsen's human embryology|year=2009|publisher=Churchill Livingstone/Elsevier|location=Philadelphia, PA |isbn=978-0-443-06811-9|chapter="Development of the Urogenital system"|edition=4th}}</ref> 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 [[fetus|fetal life]], twice as large during childhood, and decreasing to its adult size, smaller than the uterus, after puberty.<ref name=ELLIS2011 /> 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.<ref name=Cervix2006>{{cite book|title=The Cervix | veditors = Jordan J, Singer A, Jones H, Shafi M |chapter=Morphogenesis and Differentiation of the cervicovaginal epithelium | vauthors = McLean JM |url=https://books.google.com/books?id=Gbp2uRBLE9cC |isbn=978-1-4051-3137-7 |date=November 2006 |publisher=Wiley-Blackwell|edition=2nd }}</ref>{{rp|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.<ref name=Reich2014>{{cite journal | vauthors = Reich O, Fritsch H | title = The developmental origin of cervical and vaginal epithelium and their clinical consequences: a systematic review | journal = Journal of Lower Genital Tract Disease | volume = 18 | issue = 4 | pages = 358–360 | date = October 2014 | pmid = 24977630 | doi = 10.1097/LGT.0000000000000023 | s2cid = 3060493 }}</ref>

=== Histology ===
{{Anchor|Transformation zone}}
{{Multiple image
| total_width       = 270
| image1            = Histology of transformation zone mucosa.jpg
| caption1          = 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]].
| image2            = Histology of endocervix.jpg
| caption2          = Histology of endocervix, with mucinous columnar epithelium and mucinous glands. H&E stain.
}}
[[File:Nulliparous cervix with ectropion.jpg|thumb|upright=0.75|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 {{convert|3|mm|abbr=on}} 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.<ref name=Gray38/> In contrast, the ectocervix is covered with nonkeratinized stratified squamous epithelium,<ref name=Gray38/> which resembles the squamous epithelium lining the vagina.<ref name=0&G-7th/>{{rp|41}} The junction between these two types of epithelia is called the squamocolumnar junction.<ref name=0&G-7th>{{cite book |title= Obstetrics and Gynecology |edition=7th |url= https://books.google.com/books?id=dD-emqhOXa0C | vauthors = Beckmann CR, Herbert W, Laube D, Ling F, Smith R |date=March 2013 |pages=408–11 |publisher=Lippincott Williams & Wilkins |isbn= 9781451144314}}</ref>{{rp|408–11}} Underlying both types of epithelium is a tough layer of [[collagen]].<ref name=WHEATERS2006>{{cite book| vauthors = Young B |title=Wheater's functional histology: a text and colour atlas|url=https://archive.org/details/wheatersfunction00youn|url-access=limited|year=2006|publisher=Churchill Livingstone/Elsevier |location=Edinburgh, United Kingdom |isbn=978-0-443-06850-8 |edition=5th|page=[https://archive.org/details/wheatersfunction00youn/page/n851 376]}}</ref> 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.<ref name=Gray38/><!-- cites 2 previous sentences -->
<gallery mode="packed" heights="110">
File:Cervix Normal Squamocolumnar Junction (565238127).jpg|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.
File:Transformation zone types.png|Transformation zone types:<ref>International Federation for Cervical Pathology and Colposcopy (IFCPC) classification. References:<br>-{{cite web|url=https://www.rcpa.edu.au/Library/Practising-Pathology/Structured-Pathology-Reporting-of-Cancer/Docs/Transformation_zone|title=Transformation zone (TZ) and cervical excision types|website=[[Royal College of Pathologists of Australasia]]}}<br>- {{cite journal | vauthors = Jordan J, Arbyn M, Martin-Hirsch P, Schenck U, Baldauf JJ, Da Silva D, Anttila A, Nieminen P, Prendiville W | display-authors = 6 | title = European guidelines for quality assurance in cervical cancer screening: recommendations for clinical management of abnormal cervical cytology, part 1 | journal = Cytopathology | volume = 19 | issue = 6 | pages = 342–354 | date = December 2008 | pmid = 19040546 | doi = 10.1111/j.1365-2303.2008.00623.x | s2cid = 16462929 | doi-access = free }}</ref><br>Type 1: Completely ectocervical (common under hormonal influence).<br>Type 2: Endocervical component but fully visible (common before puberty).<br>Type 3: Endocervical component, not fully visible (common after menopause).
</gallery>
In [[preadolescence|prepubertal]] girls, the functional squamocolumnar junction is just within the cervical canal.<ref name=0&G-7th/>{{rp|411}} Upon entering puberty, due to hormonal influence, and during pregnancy, the columnar epithelium extends outward over the ectocervix as the cervix everts.<ref name=Cervix2006/>{{rp|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.<ref name=Cervix2006/>{{rp|106}}<ref name=0&G-7th/>{{rp|411}} The exposed columnar epithelium can undergo physiological [[metaplasia]] and change to tougher metaplastic squamous epithelium in days or weeks,<ref name=0&G-7th/>{{rp|25}} which is very similar to the original squamous epithelium when mature.<ref name=0&G-7th/>{{rp|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.<ref name=0&G-7th/>{{rp|411}} Histologically, the transformation zone is generally defined as surface squamous epithelium with surface columnar epithelium or stromal glands/crypts, or both.<ref name="pmid15917428">{{cite journal | vauthors = Mukonoweshuro P, Oriowolo A, Smith M | title = Audit of the histological definition of cervical transformation zone | journal = Journal of Clinical Pathology | volume = 58 | issue = 6 | pages = 671 | date = June 2005 | pmid = 15917428 | pmc = 1770692 }}</ref>

After menopause, the uterine structures involute, and the functional squamocolumnar junction moves into the cervical canal.<ref name=0&G-7th/>{{rp|41}}

[[Nabothian cyst]]s (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.<ref name=0&G-7th/>{{rp|410–411}} A buildup of mucus in the glands forms Nabothian cysts, usually less than about {{convert|abbr=on|5|mm}} in diameter,<ref name=Gray38/> which are considered physiological rather than pathological.<ref name=0&G-7th/>{{rp|411}} Both gland openings and Nabothian cysts are helpful to identify the transformation zone.<ref name=Cervix2006/>{{rp|106}}