First of all,. a placenta is a flattened circular organ in the uterus of pregnant eutherian mammals, nourishing and maintaining the fetus through the umbilical cord.
When a child is still in the uterus, it is a water filled environment (amniotic fluids). At that time a child cannot digest or breath and is unable to carry out excretion.
How does the child net nutrition?
It has the placental structure growing out of the developing embryo. It does not grow out of the mother.
Also, the blood vessels inside the placenta are the CHILD's blood vessels.
Things like glucose, fats and amino acids would travel through the mothers blood stream and into the wall of the uterus. These nutrients will then cross into the child's blood at the placenta.
The placenta has a large surface area and the barrier is very thin.
The child also produces molecules that are sent back into the maternal blood (e.g. CO2 and urea).
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