umbilical cord

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Connection between the embryo (or fetus) and the placenta inside the uterus of placental mammals. It has one vein and two arteries, transporting oxygen and nutrients to the developing young, and removing waste products. Blood is carried from the fetus along the umbilical cord and into the placenta. Here it is brought close to the mother's blood. Oxygen, nutrients, and antibodies from the mother diffuse (see diffusion) into the fetal blood. Waste materials from the fetus pass into the mother's blood. The fetal blood, which has been enriched with nutrients, oxygenated, and cleaned of waste, is carried back to the fetus by another blood vessel in the umbilical cord. At birth, the connection between the young and the placenta is no longer necessary. The umbilical cord drops off or is severed, leaving a scar called the navel.

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