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FETAL CIRCULATION

FETAL CIRCULATION This video is about fetal circulation and transition from fetal to neonatal circulation after birth. Three shunts are important in maintaining fetal circulation.They are ductus venosus,foramen ovale and ductus arteriosus. Placenta is the site of gas exchange in the fetus.Oxygenated blood is carried by umbilical vein from placenta.It passes through ductus venosus and IVC and drains into right atrium.Most of this blood passes through foramen ovale into left atrium, left ventricle and then into aorta.This blood perfuses upper fetal body and brain. Deoxygenated blood is carried by SVC to right atrium.It mixes with oxygenated blood and flows into right ventricle and then into pulmonary artery.Only 5% of this blood goes to lungs whereas major portion passes through ductus arteriosus into descending aorta.This blood perfuses lower fetal body and is eventually taken by umbilical arteries back to placenta for gas exchange. After birth,following first few breaths pulmonary vascular resistance falls due to pulmonary vasodilatation.When umbilical cord is cut,systemic vascular resistance rises.So,there is reversal of shunt through ductus arteriosus and eventually ductus arteriosus closes.Due to increased left atrial pressure foramen ovale also closes.Blood flow to ductus venosus ceases when cord is cut resulting in functional closure of ductus venosus.Functional closure of three shunts complete the transition to neonatal circulation.