Editing Umbilical cord (section)

==Structure and development==
[[File:Cross section of the umbilical cord.jpg|thumb|upright=1.2|Cross-sectional [[micrograph]] of the human umbilical cord. [[H&E stain]]. Labelled  ''allantoic duct'' is also known as the [[urachus]].]]
[[File:8w3d with umbilical cord.gif|thumb|170px|[[Vaginal ultrasonography]] of an embryo of a [[Gestational age (obstetrics)|gestational age]] of eight weeks and three days. The embryo is surrounded by the thin membranes of the [[amniotic sac]], the umbilical cord is seen in the center, attaching the embryo to the [[placenta]].]]

The umbilical cord develops from and contains remnants of the [[yolk sac]] and [[allantois]]. It forms by the fifth week of [[human embryogenesis|development]], replacing the yolk sac as the source of nutrients for the embryo.<ref>{{cite web |url=http://www.med.yale.edu/obgyn/kliman/placenta/articles/EOR_UC/Umbilical_Cord.html |title=The Umbilical Cord<!-- Bot generated title --> |website=yale.edu |access-date=27 March 2018 |url-status=live |archive-url=https://web.archive.org/web/20130328143634/http://www.med.yale.edu/obgyn/kliman/placenta/articles/EOR_UC/Umbilical_Cord.html |archive-date=28 March 2013}}</ref> The cord is not directly connected to the mother's circulatory system, but instead joins the [[placenta]], which transfers materials to and from the maternal blood without allowing direct mixing. The length of the umbilical cord is approximately equal to the [[crown-rump length]] of the fetus throughout [[pregnancy]]. The umbilical cord in a full term [[neonate]] is usually about {{convert|50|cm|in|abbr=off|sp=us|lk=on}} long and about {{convert|2|cm|in|sp=us}} in diameter. This diameter decreases rapidly within the placenta. The fully patent umbilical artery has two main layers: an outer layer consisting of circularly arranged smooth muscle cells and an inner layer which shows rather irregularly and loosely arranged cells embedded in abundant [[ground substance]] staining [[Metachromasy|metachromatic]].<ref name=Meyer>{{cite journal |vauthors=Meyer WW, Rumpelt HJ, Yao AC, Lind J |title=Structure and closure mechanism of the human umbilical artery |journal=Eur. J. Pediatr. |volume=128 |issue=4 |pages=247–59 |date=July 1978 |pmid=668732 |doi= 10.1007/BF00445610|s2cid=37516644 }}</ref> The smooth muscle cells of the layer are rather poorly differentiated, contain only a few tiny [[myofilament]]s and are thereby unlikely to contribute actively to the process of post-natal closure.<ref name=Meyer/>

The umbilical cord can be detected by ultrasound by six weeks of gestation and well-visualized by eight to nine weeks of gestation.<ref>{{Cite journal |last1=Moshiri |first1=Mariam |last2=Zaidi |first2=Sadaf F. |last3=Robinson |first3=Tracy J. |last4=Bhargava |first4=Puneet |last5=Siebert |first5=Joseph R. |last6=Dubinsky |first6=Theodore J. |last7=Katz |first7=Douglas S. |date=January 2014 |title=Comprehensive Imaging Review of Abnormalities of the Umbilical Cord |url=http://pubs.rsna.org/doi/10.1148/rg.341125127 |journal=RadioGraphics |language=en |volume=34 |issue=1 |pages=179–196 |doi=10.1148/rg.341125127 |pmid=24428290 |issn=0271-5333|url-access=subscription }}</ref>

The umbilical [[cord lining]] is a good source of mesenchymal and epithelial stem cells. Umbilical cord [[mesenchymal stem cell]]s (UC-MSC) have been used clinically to treat osteoarthritis, autoimmune diseases, and multiple other conditions. Their advantages include a better harvesting, and multiplication, and immunosuppressive properties that define their potential for use in transplantations. Their use would also overcome the ethical objections raised by the use of [[embryonic stem cell]]s.<ref name="Saleh">{{cite journal |last1=Saleh |first1=R |last2=Reza |first2=HM |title=Short review on human umbilical cord lining epithelial cells and their potential clinical applications. |journal=Stem Cell Research & Therapy |date=10 October 2017 |volume=8 |issue=1 |pages=222 |doi=10.1186/s13287-017-0679-y |pmid=29017529 |pmc=5634865 |doi-access=free }}</ref>

The umbilical cord contains [[Wharton's jelly]], a gelatinous substance made largely from [[mucopolysaccharides]] that protects the blood vessels inside. It contains one vein, which carries oxygenated, nutrient-rich blood to the fetus, <!--
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WARNING!

On multiple occasions, people have changed this section of text to state that the umbilical arteries carry oxygenated blood to the fetus, and that the umbilical vein carries deoxygenated blood away. THIS IS INCORRECT. The article as it stands is correct, as the nomenclature reflects the fact that the umbilical arteries carry blood from the fetal heart, while the umbilical vein carries blood towards it.

Please pick up a copy of Gray's Anatomy before making a fool of yourself and wrecking the article in the process. Who is the person wrecking the article by not READING that the umbilical cord has TWO veins and ONE artery?  The Umbilical cord does NOT have 2 veins and 1 artery, but the opposite.<ref>http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/SymptomsDiagnosisofCongenitalHeartDefects/Fetal-Circulation_UCM_315674_Article.jsp#.WHGPgPkrLIU {{Bare URL inline|date=May 2022}}</ref>
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--> and two arteries that carry deoxygenated, nutrient-depleted blood away.<ref>{{cite web |url=http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/SymptomsDiagnosisofCongenitalHeartDefects/Fetal-Circulation_UCM_315674_Article.jsp#.WHGPgPkrLIU|title=Fetal Circulation |website=www.heart.org |access-date=27 March 2018 |url-status=live |archive-url=https://web.archive.org/web/20171222042027/http://www.heart.org/HEARTORG/Conditions/CongenitalHeartDefects/SymptomsDiagnosisofCongenitalHeartDefects/Fetal-Circulation_UCM_315674_Article.jsp#.WHGPgPkrLIU |archive-date=22 December 2017}}</ref> Occasionally, only two vessels (one vein and one artery) are present in the umbilical cord. This is sometimes related to fetal abnormalities, but it may also occur without accompanying problems.

It is unusual for a vein to carry oxygenated blood and for arteries to carry deoxygenated blood (the only other examples being the [[pulmonary veins]] and [[pulmonary arteries|arteries]], connecting the lungs to the heart). However, this naming convention reflects the fact that the umbilical vein carries blood towards the fetus' heart, while the umbilical arteries carry blood away.

The blood flow through the umbilical cord is approximately 35 ml / min at 20 weeks, and 240 ml / min at 40 [[Gestational age (obstetrics)|weeks of gestation]].<ref name=kiserud2004>{{Cite journal |last1 = Kiserud |first1 = T. |last2 = Acharya |first2 = G. |doi = 10.1002/pd.1062 |title = The fetal circulation |journal = Prenatal Diagnosis |volume = 24 |issue = 13 |pages = 1049–1059 |year = 2004 |pmid = 15614842 |s2cid = 25040285 }}</ref> Adapted to the weight of the fetus, this corresponds to 115 ml / min / kg at 20 weeks and 64 ml / min / kg at 40 weeks.<ref name=kiserud2004/>

For [[Anatomical terms of location|terms of location]], the ''proximal'' part of an umbilical cord refers to the segment closest to the embryo or fetus in embryology and fetal medicine, and closest to the placenta in placental pathology, and opposite for the ''distal'' part, respectively.<ref>{{cite web |url=https://patholines.org/Placenta |title=Placenta |website=patholines.org |access-date=2023-04-07 |author=Mikael Häggström, MD |date=2020-08-27}}</ref>