DAVID NUNUK / SCIENCE PHOTO LIBRARY DAVID NUNUK / SCIENCE PHOTO LIBRARY
Placenta. Bloody hand holding a human placenta by the umbilical cord (upper centre). The placenta (bottom centre) is a vascular organ. It consists of a ramification of blood vessels and capillaries encased in a membrane. The placenta is responsible for the respiration and excretion of the growing foetus. Blood flows to and from the foetus via the umbilical cord to the placenta. There the network of capillaries are surrounded by pools of the mother's blood. Carbon dioxide and other wastes diffuse out of the foetal blood and into the mother's blood. Oxygen and other nutrients diffuse into the foetal blood. The foetal blood and mother's blood do not mix.
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