Foetal Circulation

Blood from the placenta to the foetus Through the umbilical vein Near liver most goes to the IVC directly Through ductus venosus

Foetal Circulation

Foetal circulation in heart and great vessels

Blood from the placenta 80 % saturated with oxygen Goes through umbilical vein Near liver most of the blood flows through the ductus venosus directly into the IVC A smaller amount enters liver There it mixes with blood from portal vein

In the inferior vena cava the oxygenated blood from the placenta mixes with the deoxygenated blood from the lower limbs. The umbilical vein then enters the right atrium. Through oval foramen most of the blood enters the left atrium directly Only a small amount remains in the right atrium due to the action of lower edge of septum secondum. In the right atrium the blood mixes with the deoxygenated blood from the head and neck which arrives through the superior vena cava.

In the left atrium the blood mixes with a small quantity of deoxygenated blood from the pulmonary vein Blood from left atrium enters the left ventricle ascending aorta Coronary artery and the carotid arteries supplying important organs get blood that flows directly from the left ventricle.

Desaturated blood from superior vena cava  right ventricle pulmonary trunk In foetal life lung stays collapsed – resistance in the pulmonary vessels is high – hence most of the blood passes directly through the ductus arteriosus into the descending aorta. Descending aorta  towards placenta by way of the two umbilical arteries

Oxygen saturation saturation in the umbilical arteries is approximately 58 % The places where the oxygenated blood from the placenta mixes with deoxygenated blood : In the liver IVC Right atrium Left atrium At the point of entry of ductus arteriosus into the descending aorta

Circulatory changes at birth : - Cessation of blood flow from the placenta – closure of umbilical veins and ductus venosus and obliteration of umbilical vein forming the ligamentum teres hepatis in the lower margin of the falcifrorm ligament Respiration starts Ductus arteriosus closes by muscular contraction of its wall. The amount of blood flow through the lung vessels increases rapidly Pressure in left atrium increases As a result of interruption of placental blood flow pressure in the right atrium decreases

Septum primum is then apposed to the septum secondum and functionally the oval foramen closes. Salient Features Ductus venosus Foramen ovale Ductus arteriosus Mixing in Inferior vena cava Right atrium Left atrium Descending aorta

The Beginning