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Function of the placenta
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During pregnancy, a single organ serves as the point of exchange between the pregnant person and the developing child: the placenta. There, three things pass between the two: nutrients, waste, and gases.
That exchange happens in one precise place: the surface of the chorionic villi. Some substances cross on their own, by simple diffusion, which is the natural movement of a substance from where it is more concentrated toward where it is less concentrated. Others, like iron, do not cross on their own: they have to be pushed, and that is called active transport. And there is one more thing: the two blood supplies never mix directly, because blood cells cannot cross. They sit as close as two hands separated by a glove, touching without touching.
In brief
The placenta is the organ where nutrients, waste, and gases are exchanged between the pregnant person and the developing child.
Exchange happens at the surface of the chorionic villi: some substances cross by simple diffusion, and others, like iron, by active transport.
Maternal and fetal blood never mix directly, because blood cells cannot cross the placenta.
The two circulations sit as close as two hands separated by a glove: what diffuses crosses, but the blood never touches.
Sources (1)
- OpenStax, Rice University28.2 Embryonic DevelopmentPublished
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