What Is the Umbilical Cord?
Inside the womb of a pregnant woman or animal, a placenta is formed, through which the unborn baby is nourished. The baby is connected to the placenta by the umbilical cord (also called the navel string, birth cord or funiculus umbilicalis), which is joined to the unborn child at the navel.
The umbilical cord is the baby’s lifeline. Everything the child needs to survive will pass through it-air, blood and nourishment. At most it is no more than an inch wide and, perhaps, only a foot long.
Once the baby is born the placenta, which serves a purpose only during the pregnancy, will be discarded. The umbilical cord will be cut with scissors a few inches away from the newborn baby’s stomach. This is quite painless because the umbilical cord has no nerves and it leaves an umbilical stump attached to baby’s belly button. The baby will now breathe on its own. The stump will dry up and drop off in about 7 to 21 days, leaving a small wound that may take a few days to heal.
In placental mammals, the umbilical cord is a conduit between the developing embryo or fetus and the placenta. During prenatal development, the umbilical cord is physiologically and genetically part of the fetus and, (in humans), 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 fetal heart pumps deoxygenated, nutrient-depleted blood through the umbilical arteries back to the placenta.
The umbilical cord develops from and contains remnants of the yolk sac and allantois (and is therefore derived from the zygote). It forms by the fifth week of fetal development, replacing the yolk sac as the source of nutrients for the fetus. The cord is not directly connected to the mother’s circulatory system, but instead joins the placenta, which transfers materials to and from the mother’s 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 50 centimeters (20 in) long and about 2 centimeters (0.75 in) 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 metachromatic.
The smooth muscle cells of the layer are rather poorly differentiated, contain only a few tiny myofilaments and are thereby unlikely to contribute actively to the process of postnatal closure.
The umbilical cord contains Wharton’s jelly, a gelatinous substance made largely from mucopolysaccharides which protects the blood vessels inside. It contains one vein, which carries oxygenated, nutrient-rich blood to the fetus, and two arteries that carry deoxygenated, nutrient-depleted blood away. 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, 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 weeks of gestation. 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.