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The placental bulk's core is where the umbilical lead inserts after being attached to the fetus at the umbilicus.
Its diameter is 1-2 cm, and its length is typically 55–60 cm. The umbilical lead, which consists of one umbilical vein and two paired umbilical arteries, is a group of blood veins encased in a tubular sheath of amnion.
The yolk sac and the allantois give rise to and are preserved in the umbilical cord. By the fifth week of development, it has formed and is the embryo's new source of nutrition, taking the place of the yolk sac.
The cord joins the placenta, which transports substances to and from the mother's blood without allowing them to directly mix, rather than being directly attached to the mother's circulatory system. The
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