A fetus (baby) is fed, or nourished, by the mother through the
placenta, which is attached to the umbilical cord. In the placenta, the
mother's blood and the fetal blood both flow through vessels that are very
close together. But the mother's blood does not mix with the fetal blood. When
the mother's blood is close to the fetal blood, oxygen and nutrients move from
the mother's blood into the fetal blood.
As the blood flows through the fetus, it picks up waste products and
returns to the mother through the umbilical cord. The blood (with waste
products from the fetus) goes through the mother's lungs and liver, where waste
products are removed.
Since oxygen is supplied by the mother, the fetus does not use lungs
to breathe. Only a small amount of blood flows to the fetus's lungs. After
birth, blood must flow to the baby's lungs. Before birth, the mother's liver
removes waste products for the fetus, so less blood flows through the fetus's
Blood flows around the fetus's lungs and liver by going through an
opening in the heart and through two extra blood vessels. This opening (called
the foramen ovale) and the extra blood vessels (called the ductus arteriosus
and the ductus venosus) normally close after birth.
Illustrations copyright 2000 by Nucleus
Communications, Inc. All rights reserved.
October 11, 2011
John Pope, MD - Pediatrics & Larry A. Latson, MD - Pediatric Cardiology
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