Fetal CirculationFetal Circulation

Fetal Fetal CirculatioCirculationn

Salient Features of Salient Features of Fetal Growth Fetal Growth

• Placenta is very active.Placenta is very active.• Liver and lungs are passive.Liver and lungs are passive.• Head is growing faster.Head is growing faster.

Hemodynamics of Fetal Hemodynamics of Fetal CirculationCirculation

• Venous and arterial blood mix up in atriaVenous and arterial blood mix up in atria

• The venacava carries mixed blood to the The venacava carries mixed blood to the right atrium bypassing liver and lungs.right atrium bypassing liver and lungs.

• Aorta carries mixed blood back to Aorta carries mixed blood back to placentaplacenta

• Blood circulation in the fetus is never as Blood circulation in the fetus is never as saturated with oxygen as that blood saturated with oxygen as that blood circulating through the adult. That is, circulating through the adult. That is, difference in oxygen tension between difference in oxygen tension between blood of the umbilical arteries is much blood of the umbilical arteries is much less than that of adult venous and less than that of adult venous and arterial blood.arterial blood.

Fetal Fetal CirculatioCirculationn

• The arterial blood flows to the fetus The arterial blood flows to the fetus through the umbilical vein. through the umbilical vein.

• It passes to the undersurface of liver and It passes to the undersurface of liver and separates in to two branches. separates in to two branches.

• Lager is joined by the portal vein and Lager is joined by the portal vein and enters the right lobe of the liver.enters the right lobe of the liver.

• The other continued upwards as ductus The other continued upwards as ductus venosus and joins the inferior venacava.venosus and joins the inferior venacava.

• In the inferior venacava blood carried by In the inferior venacava blood carried by the ductus venosus and hepatic veins the ductus venosus and hepatic veins becomes mixed with blood returning from becomes mixed with blood returning from the lower extremities, so it is a mixture the lower extremities, so it is a mixture of oxygenated and de oxygenated blood of oxygenated and de oxygenated blood

Course of Fetal CirculationCourse of Fetal Circulation Pre-delivery phasePre-delivery phase

• It enters the right atrium and is directed It enters the right atrium and is directed through the foramen ovale into the left through the foramen ovale into the left atrium. In the left atrium, it mixes with a atrium. In the left atrium, it mixes with a small quantity of blood returning from the small quantity of blood returning from the lungs through the pulmonary veins. lungs through the pulmonary veins.

• From the left atrium, blood passes into From the left atrium, blood passes into the left ventricle, and from the left the left ventricle, and from the left ventricle into the aorta. From the aortal it ventricle into the aorta. From the aortal it is distributed almost entirely to the head is distributed almost entirely to the head and upper extremities – a small quantity and upper extremities – a small quantity of blood continuing into the descending of blood continuing into the descending aorta. aorta.

Continued Continued

• After circulation in the head and upper After circulation in the head and upper extremities, blood is returned by the extremities, blood is returned by the superior vena cava to the right atrium, superior vena cava to the right atrium, where it mixes with a small portion of that where it mixes with a small portion of that blood entering from the inferior vena blood entering from the inferior vena cava.cava.

• From the right atrium it descends into the From the right atrium it descends into the right ventricle and passes into the main right ventricle and passes into the main pulmonary artery.pulmonary artery.

• From the pulmonary artery, most of the From the pulmonary artery, most of the blood passes trough the ductus arterioss blood passes trough the ductus arterioss into the aorta, where it mixes with blood into the aorta, where it mixes with blood from the left ventricle. from the left ventricle.

Continued Continued

• Some of the blood with main pulmonary Some of the blood with main pulmonary artery is distributed to the lungs by the artery is distributed to the lungs by the right and left pulmonary arteries. The right and left pulmonary arteries. The pulmonary veins returns this blood the the pulmonary veins returns this blood the the left atrium.left atrium.

• The blood passing from the main pulmonary The blood passing from the main pulmonary artery through the ductus arteries descends artery through the ductus arteries descends through the aorta and is in part distributed through the aorta and is in part distributed to the lower extremities and viscera of the to the lower extremities and viscera of the abdomen and pelvis. The greater amount is abdomen and pelvis. The greater amount is conveyed by the hypogastric arteries to the conveyed by the hypogastric arteries to the umbilical arteries The umbilical arteries umbilical arteries The umbilical arteries return the blood to the placenta.return the blood to the placenta.

Continued Continued

Intermediate Phase Intermediate Phase • Immediately after delivery , the baby begins to Immediately after delivery , the baby begins to

breathe, and pulmonary circulation changes, An breathe, and pulmonary circulation changes, An increased quantity of blood is pumped into the increased quantity of blood is pumped into the pulmonary arteries by the right ventricle, and a pulmonary arteries by the right ventricle, and a smaller quantity passes through the ductus smaller quantity passes through the ductus arteriosus. The ductus arteriosus begins to arteriosus. The ductus arteriosus begins to atrophy, eventually becoming the ligamentum atrophy, eventually becoming the ligamentum arteriosumarteriosum.

• Pulmonary circulation increases, and more blood Pulmonary circulation increases, and more blood is returned from the lungs to the left atrium. is returned from the lungs to the left atrium. Pressure rises in the left atrium, causing the Pressure rises in the left atrium, causing the foramen ovale to close. Placental circulation foramen ovale to close. Placental circulation ceases to function as soon as the umbilical cord ceases to function as soon as the umbilical cord is tied. The ends of the hypogastric arteries is tied. The ends of the hypogastric arteries atrophy, and these vessels become the hypo-atrophy, and these vessels become the hypo-gastric ligaments. gastric ligaments.

Adult PhaseAdult Phase

• Closure of ductus arterosus in early Closure of ductus arterosus in early postnatal period due to reflex action postnatal period due to reflex action secondary to increased oxygen tension and secondary to increased oxygen tension and the interaction of prosta glandinthe interaction of prosta glandin

PDA machinery murmurPDA machinery murmur

• Obliteration of foramen ovale – 6 to 8 weeksObliteration of foramen ovale – 6 to 8 weeks

Patent foramen ovale with few or no Patent foramen ovale with few or no symptoms symptoms

• Occluded umblical vein – ligamentum teres Occluded umblical vein – ligamentum teres

• Obliterated ductus venosus – ligamentum Obliterated ductus venosus – ligamentum venosumvenosum

Hemodynamics of Hemodynamics of Normal AdultNormal Adult

• Venous and arterial blood no longer mix Venous and arterial blood no longer mix in the atriain the atria

• The venacava carries only deoxygenated The venacava carries only deoxygenated blood into the right atrium and right blood into the right atrium and right ventricle which is pumped to the ventricle which is pumped to the pulmonary arteries and finally to the pulmonary arteries and finally to the pulmonary capillariespulmonary capillaries

• Aorta carries only oxygenated blood from Aorta carries only oxygenated blood from the left heart via the pulmonary veins for the left heart via the pulmonary veins for distribution to the rest of the body.distribution to the rest of the body.

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