Editing Cervix (section)

=== 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}}