What Happens During Prenatal Circulation?
Before a baby is born, its mother supplies it with oxygen-rich blood that the heart then pumps through body. Learn more about prenatal circulation and the fetal circulatory system.
Transcript: What Happens During Prenatal Circulation?
The Fetal Circulatory System
The heart and circulatory system of a fetus begin to form soon after conception. By the end of the fifth week, the heart of the fetus is able to pump blood throughout its body. However, since the lungs will not function until birth when the newborn takes its first breath, the mother must supply the fetus with oxygen-rich blood.What Are the Foramen Ovale and the Ductus Arteriosus?
As in an adult heart, the prenatal heart develops four chambers and four valves. But because the fetal lungs will not be used until after birth, blood must bypass the lungs. Two structures develop in the prenatal heart that allow the blood to be routed around the lungs: the foramen ovale and the ductus arteriosus. The foramen ovale is a hole that exists between the left and right atria. The ductus arteriosus is a blood vessel that connects the aorta to the pulmonary artery.Circulation Through the Fetus' Vena Cava
In normal prenatal circulation, oxygen-rich blood is delivered from the mother's body, through the placenta and umbilical cord, to the inferior vena cava of the fetus. The vena cava also receives oxygen-poor blood from the body of the fetus. Both oxygen-rich blood and oxygen-poor blood travel through the vena cava to the right atrium.Circulation Through the Aorta
Most of the mixed blood in the right atrium is pushed through the foramen ovale and into the left atrium. From there, it moves into the left ventricle, which pumps the blood into the aorta. The aorta then delivers the blood to the body of the fetus.The remaining blood in the right atrium enters the right ventricle, which pumps it into the pulmonary artery, leading to the lungs. But since the lungs are not yet functioning, the blood is directed from the pulmonary artery through the ductus arteriosus, and into the aorta. Again, the aorta delivers the blood to the body of the fetus.