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| Umbilical cord | ||
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| The sinew-like cord stump of a seven-day-old baby | ||
| Latin | funiculus umbilicalis, chorda umbilicalis | |
| Days | 29 | |
| Dorlands/Elsevier | c_55/12259050 | |
In placental mammals, the umbilical cord (also called the birth cord) is the tube that connects a developing embryo or fetus to the placenta. It normally contains two arteries (the umbilical arteries) and one vein (the umbilical vein), buried within Wharton\'s jelly. The umbilical vein supplies the fetus with oxygenated, nutrient-rich blood from the placenta. Conversely, the umbilical arteries return the deoxygenated, nutrient-depleted blood.
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The umbilical cord develops from the same sperm and ovum from which the placenta and fetus develop, and contains remnants of the yolk sac and allantois. It forms by the fifth week of fetal development, replacing the yolk sac as the source of nutrients for the fetus.http://www.med.yale.edu/obgyn/kliman/placenta/articles/EOR_UC/Umbilical_Cord.html In humans, the umbilical cord in a full term neonate is usually about 50 centimetres (19.7 in) long and about 2 centimetres (0.75 in) diameter, shrinking rapidly in diameter in the after birth.
The umbilical cord is composed of Wharton\'s jelly, and not of ordinary skin and connective tissue. The cord contains one vein, which carries oxygenated, nutrient-rich blood (from the mother to the fetus) and two arteries that carry deoxygenated, nutrient depleted blood (from the fetus back to the mother). 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 arteries, connecting the lungs to the heart). However, this naming convention reflects the fact that the umbilical vein carries blood towards the fetus\'s heart, whilst the umbilical artery carries blood away.
The umbilical vein continues towards the transverse fissure of the liver, where it splits into two. One of these branches joins with the hepatic portal vein, which carries blood into the liver. The second branch (known as the ductus venosus) allows the majority of the incoming blood (approximately 80%) to bypass the liver and flow directly 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 before joining the umbilical cord.
Shortly after birth, upon exposure to temperature change, the gelatinous Wharton\'s Jelly substance undergoes a physiological change that collapses previous structure boundaries and in effect creates a natural clamp on the umbilical cord which halts placental blood return to the neonate, causing the cord to cease pulsation. This process will take as little as five minutes if left to proceed naturally. However, under usual obstetric practice, this will normally be preceded by artificial clamping of the cord.
A number of abnormalities can affect the umbilical cord, which can cause problems that affect both mother and child:
General obstetric practice introduces artificial clamping as early as 1 minute after birth of the child. This is followed by cutting of the cord, which is painless due to the lack of any nerves. The cord is extremely tough, like thick sinew, and so cutting it requires a suitably sharp instrument. Provided that umbilical severance occurs after the cord has stopped pulsing (5-20 minutes after birth), there is ordinarily no significant loss of either infant or maternal blood while cutting the cord.
Umbilical cord clamp
There are umbilical cord clamps which combine the cord clamps with the knife. These clamps are safer and faster, allowing one to first apply the cord clamp and then cut the umbilical cord. After the cord is clamped and cut, the newborn wears a plastic clip on the navel area until the compressed region of the cord has dried and sealed sufficiently. The remaining umbilical stub remains for up to 2–3 weeks as it dries and then falls off.
The health benefits of non-clamping of the cord and delayed umbilical severance are receiving attention in medical journals.Hohmann M. (1985). "Early or late cord clamping? A question of optimal time" (Article in German). Wiener Klinische Wochenschrift, 97(11):497-500. PMID 4013344. Mercer J.S., B.R. Vohr, M.M. McGrath, J.F. Padbury, M. Wallach, W. Oh (2006). "Delayed cord clamping in very preterm infants reduces the incidence of intraventricular hemorrhage and late-onset sepsis: a randomized, controlled trial." Pediatrics, 117(4):1235-42. PMID 16585320.Hutton E.K., E.S. Hassan (2007). "Late vs early clamping of the umbilical cord in full-term neonates: systematic review and meta-analysis of controlled trials." Journal of the American Medical Association, 297(11):1257-58. PMID 17374818. In nonseverance scenarios, also called lotus birth, the umbilical cord is wrapped up to within an inch of the newborn\'s belly, and the entire intact cord is allowed to dry like a sinew, which then falls off.Crowther S (2006). "Lotus birth: leaving the cord alone." The Practising Midwife, 9(6):12-14. PMID 16830839.
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The neutrality of this section is disputed. Please see the discussion on the talk page. This section has been tagged since January 2008. |
Recently, it has been discovered that the blood within the umbilical cord, known as cord blood, is a rich and readily available source of primitive, undifferentiated stem cells (i.e. CD34-positive and CD38-negative). These cord blood cells can be used for bone marrow transplant.
Others have chosen to have this blood diverted from the baby\'s umbilical blood transfer through early cord clamping and cutting, to freeze for long-term (and costly) storage at a cord blood bank should the child ever require the cord blood stem cells (for example, to replace bone marrow destroyed when treating leukemia). This practice is somewhat controversial,[citation needed] with critics asserting that early cord blood withdrawal actually increases the likelihood of childhood disease. The Royal College of Obstetricians and Gynaecologists 2006 opinion states, "There is still insufficient evidence to recommend directed commercial cord blood collection and stem-cell storage in low-risk families."
In the future, cord blood-derived embryonic-like stem cells (CBEs) may also be banked and matched with other patients, much like blood and transplanted tissues. The use of CBEs would eliminate the ethical difficulties associated with embryonic stem cells (ESCs)."Cord blood yields \'ethical\' embryonic stem cells.", Coghlin A. New Scientist, August 18, 2005. Accessed June 25, 2007.
In other mammals, the mother animal generally will gnaw the cord off[citation needed] separating the placenta from the baby. It is often consumed by the mother, which nourishes her, and disposes of tissues that would attract scavengers or predators. In chimpanzees, the mother focuses no attention on umbilical severance, instead staying still and nursing and holding her baby (with cord, placenta, and all) until the cord dries and separates within a day of birth, at which time she leaves the cord and placenta on the forest floor where it is recycled by scavengers. This was first documented by zoologists in the wild in 1974.[citation needed]
The term "umbilical cord" or just "umbilical" has also come to be used for other cords with similar functions, such as the hose connecting a surface-supplied diver to his surface supply of air and/or heating, or a space-suited astronaut to his spacecraft.
The phrase "cutting the umbilical cord" is used metaphorically to describe a child\'s breaking away from the parental home.
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Diagram illustrating a later stage in the development of the umbilical cord. |
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Fetus of about eight weeks, enclosed in the amnion. Magnified a little over two diameters. |
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Sectional plan of the gravid uterus in the third and fourth month. |
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Fetus in utero, between fifth and sixth months. |
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Scheme of placental circulation. |
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Human embryo with heart and anterior body-wall removed to show the sinus venosus and its tributaries. |
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