The baby navel cord grows from and contains a small part of the yolk sac and allantois (and is therefore derived from the same zygote as the fetus). It is formed by the fifth week of the development of the fetus, replacing the yolk sac as the source of nutrients for the fetus. The baby baby navel cord is not directly connected to the mother’s circulatory system, but does join the placenta, which transfers materials from and to the mother’s blood without allowing direct mixtures. The length of the baby navel cord is approximately equal to the crown-rump length of the fetus throughout pregnancy. The baby navel cord is usually about 50 centimeters (20 in) long and is around 2 centimeters (0.75 in) in diameter. This diameter decreases rapidly within the placenta. The fully patent navel 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 baby navel cord is composed of Wharton’s jelly, a gelatinous substance made largely from mucopolysaccharides. 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 baby navel 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 navel vein carries blood towards the fetus’s heart, while the navel arteries carry blood away.
The blood that flows through the baby navel cord is about 35 ml / min at 20 weeks, and 240 ml / min at 40 weeks of gestation. Corresponding to the weight of the fetus, this corresponds to 115 ml / min / kg at 20 weeks and 64 ml / min / kg at 40 weeks.
