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FETAL CIRCULATION

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• Introduction to fetal circulation

• Throughout the fetal stage of development, the maternal blood supplies the fetus with O2 and nutrients and carries away its wastes.

Fetal Circulation OH-98 -In the fetal circulatory system, the umbilical vein transports blood rich in O2 and nutrients from the placenta to the fetal body.

–The umbilical vein enters the body through the umbilical ring and travels along the anterior abdominal wall to the liver.

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- There, the oxygenated blood from the placenta is mixed with the deoxygenated blood from the lower parts of the body.

- This mixture continues through the vena cava to the right atrium.

–In the adult heart, blood flows from the right atrium to the right ventricle then through the pulmonary arteries to the lungs.

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• As the blood from the inferior vena cava enters the right atrium, a large proportion of it is shunted directly into the left atrium through an opening called the foramen ovale.

•Only a small volume of blood enters the pulmonary circuit, because the lungs are collapsed, and their blood vessels have a high resistance to flow.

•the blood is prevented from entering the portion of the aorta that provides branches leading to the brain.

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•The blood carried by the descending aorta is partially oxygenated and partially deoxygenated.

•Some of it is carries into the branches of the aorta that lead to various parts of the lower regions of

the body. •The rest passes into the umbilical arteries,

which branch from the internal iliac arteries and lead to the placenta.

•There the blood is reoxygenated.

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Fetal Circulation

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Fetal Circulation

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Fetal Circulation

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• The Newborn

• The initial inflation of the lungs causes important changes in the circulatory system.

• Inflation of the lungs reduces the resistance to blood flow through the lungs resulting in increases blood flow from the pulmonary arteries.

• Consequently, an increased amount of blood flows from the right atrium to the right ventricle and into the pulmonary arteries and less blood flows through the foramen ovale to the left atrium.

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• In addition, an increased volume of blood returns from the lungs through the pulmonary veins to the left atrium, which increases the pressure in the left atrium.

• The increased left atrial pressure and decreased right atrial pressure (due to pulmonary resistance) forces blood against the septum primum causing the foramen ovale to close.

• This action functionally completes the separation of the heart into two pumps--right and left sides of the heart.