With the first breaths of life, the lungs begin to expand. In the placenta, carbon dioxide and waste products are released into the mother's circulatory system, and oxygen and nutrients from the mother's blood are released into the fetus' blood.Īt birth, the umbilical cord is clamped and the baby no longer receives oxygen and nutrients from the mother. This blood then enters the umbilical arteries and flows into the placenta. Most of the circulation to the lower body is supplied by blood passing through the ductus arteriosus. Most of this blood is bypassed or shunted away from the lungs through the ductus arteriosus to the aorta. As a result, only a small amount of the blood continues on to the lungs. In the fetus, the placenta does the work of breathing instead of the lungs. About two thirds of the blood will pass through the foramen ovale as described above, but the remaining one third will pass into the right ventricle, toward the lungs. After circulating there, the blood returns to the right atrium of the heart through the superior vena cava.
When the blood enters the right atrium, most of it flows through the foramen ovale into the left atrium.īlood then passes into the left ventricle (lower chamber of the heart) and then to the aorta, (the large artery coming from the heart).įrom the aorta, blood is sent to the heart muscle itself in addition to the brain. Waste products from the fetal blood are transferred back across the placenta to the mother's blood.īlood enters the right atrium, the chamber on the upper right side of the heart. A small amount of this blood goes directly to the liver to give it the oxygen and nutrients it needs. Most of this blood is sent through the ductus venosus, also a shunt that passes highly oxygenated blood through the liver to the inferior vena cava and then to the right atrium of the heart. The blood then reaches the inferior vena cava, a major vein connected to the heart. The enriched blood flows through the umbilical cord to the liver and splits into three branches. Oxygen and nutrients from the mother's blood are transferred across the placenta to the fetus. The shunts that bypass the lungs are called the foramen ovale, which moves blood from the right atrium of the heart to the left atrium, and the ductus arteriosus, which moves blood from the pulmonary artery to the aorta. The purpose of these shunts is to bypass certain body parts? in particular, the lungs and liver ? that are not fully developed while the fetus is still in the womb. The fetal circulatory system uses two right to left shunts, which are small passages that direct blood that needs to be oxygenated. Waste products and carbon dioxide from the fetus are sent back through the umbilical cord and placenta to the mother's circulation to be eliminated. Through the blood vessels in the umbilical cord, the fetus receives all the necessary nutrition, oxygen, and life support from the mother through the placenta. The fetus is connected by the umbilical cord to the placenta, the organ that develops and implants in the mother's uterus during pregnancy. During pregnancy, the fetal circulatory system works differently than after birth:
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