Editing Umbilical cord (section)

==Function==
===Connection to fetal circulatory system===
The umbilical cord enters the fetus via the [[Human abdomen|abdomen]], at the point which (after separation) will become the [[navel|umbilicus]] (belly button or navel). Within the fetus, the umbilical vein continues towards the [[Transverse fissure of liver|transverse fissure]] of the [[liver]], where it splits into two. One of these branches joins with the [[hepatic portal vein]] (connecting to its left branch), which carries blood into the liver. The second branch (known as the [[ductus venosus]]) bypasses the liver and flows into the [[inferior vena cava]], which carries blood towards the heart. The two umbilical arteries branch from the [[internal iliac arteries]] and pass on either side of the [[urinary bladder]] into the umbilical cord, completing the circuit back to the placenta.<ref>{{cite web|url=http://education.yahoo.com/reference/gray/subjects/subject/139 |title=Peculiarities in the Vascular System in the Fetus – Gray's Anatomy of the Human Body – Yahoo! Education |url-status=dead |archive-url=https://web.archive.org/web/20120123194946/http://education.yahoo.com/reference/gray/subjects/subject/139 |archive-date=January 23, 2012 }}</ref>

===Changes after birth===
After birth, the umbilical cord stump will dry up and drop away by the time the baby is three weeks old.<ref name=":0">{{Cite web |title=Umbilical cord care: Do's and don'ts for parents |url=https://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/in-depth/umbilical-cord/art-20048250 |access-date=2022-06-12 |website=Mayo Clinic |language=en}}</ref> If the stump still has not separated after three weeks, it might be a sign of an underlying problem, such as an infection or immune system disorder.<ref name=":0" />

In absence of external interventions, the umbilical cord [[Vascular occlusion|occludes]] physiologically shortly after birth, explained both by a swelling and collapse of [[Wharton's jelly]] in response to a reduction in temperature and by [[vasoconstriction]] of the blood vessels by smooth muscle contraction. In effect, a natural clamp is created, halting the flow of blood. In air at 18&nbsp;°C, this physiological clamping will take three minutes or less.<ref>{{cite journal|last=Cohain|first=J. S.|title=A Proposed Protocol for Third Stage Management – Judy's 3,4,5,10 minute method|journal=Birth|year=2010|volume=37|issue=1|pages=84–85|doi=10.1111/j.1523-536x.2009.00385_2.x|pmid=20402731}}</ref> In [[water birth]], where the water temperature is close to body temperature, normal pulsation can be five minutes and longer.<!--http://www.webmedcentral.com/article_view/2993-->

Closure of the umbilical artery by vasoconstriction consists of multiple constrictions which increase in number and degree with time. There are segments of dilations with trapped uncoagulated blood between the constrictions before complete occlusion.<ref>{{cite journal |vauthors=Yao AC, Lind J, Lu T |title=Closure of the human umbilical artery: a physiological demonstration of Burton's theory |journal=Eur. J. Obstet. Gynecol. Reprod. Biol. |volume=7 |issue=6 |pages=365–8 |year=1977 |pmid=264063 |doi= 10.1016/0028-2243(77)90064-8}}</ref> Both the partial constrictions and the ultimate closure are mainly produced by muscle cells of the outer circular layer.<ref name=Meyer/> In contrast, the inner layer seems to serve mainly as a plastic tissue which can easily be shifted in an [[Anatomical directions|axial]] direction and then folded into the narrowing lumen to complete the closure.<ref name=Meyer/> The vasoconstrictive occlusion appears to be mainly mediated by [[serotonin]]<ref name=Quan/><ref name=white>{{cite journal |author=White RP |title=Pharmacodynamic study of maturation and closure of human umbilical arteries |journal=Am. J. Obstet. Gynecol. |volume=160 |issue=1 |pages=229–37 |date=January 1989 |pmid=2912087 |doi= 10.1016/0002-9378(89)90127-0}}</ref> and [[thromboxane A2|thromboxane A<sub>2</sub>]].<ref name=Quan>{{cite journal |vauthors=Quan A, Leung SW, Lao TT, Man RY |title=5-hydroxytryptamine and thromboxane A2 as physiologic mediators of human umbilical artery closure |journal=J. Soc. Gynecol. Investig. |volume=10 |issue=8 |pages=490–5 |date=December 2003 |pmid=14662162 |doi= 10.1016/S1071-5576(03)00149-7}}</ref> The artery in cords of preterm infants contracts more to [[angiotensin II]] and [[arachidonic acid]] and is more sensitive to [[oxytocin]] than in term ones.<ref name=white/> In contrast to the contribution of Wharton's jelly, cooling causes only temporary vasoconstriction.<ref name=white/>

Within the child, the umbilical vein and ductus venosus close up, and degenerate into fibrous remnants known as the [[round ligament of the liver]] and the [[ligamentum venosum]] respectively. Part of each umbilical artery closes up (degenerating into what are known as the [[medial umbilical ligament]]s), while the remaining sections are retained as part of the circulatory system.