1. Foetal Circulation

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

6. Foetal Circulation

7. Foetal circulation in heart and great vessels

12. 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

13. 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.

14. 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.

15. 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

16. 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

17. 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

18. 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

20. The Beginning