Placenta
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The placenta is a temporary organ found in most female mammals while they are pregnant.
The placenta has two parts, one of which is genetically and biologically part of the fetus, the other part of the mother. It is implanted in the wall of the uterus, where it receives nutrients and oxygen from the mother's blood and passes out waste. This forms a barrier called the placental barrier, which filters out some substances which could harm the fetus. However, many other substances are not filtered out, including alcohol and some chemicals associated with smoking cigarettes. Several types of viruses may also cross this barrier.
The placenta is connected to the fetus by the umbilical cord which is made of blood vessels and connective tissue. When the fetus is delivered, the placenta is delivered afterwards, and is often called the afterbirth.
