Question

Explain the differences between the circulatory system of a fetus and that of a new born baby.  

Answer 1

The growing fetus is fully dependent on placenta for nourishment. The umbilical cord links the placenta to the fetus. The mother’s blood flows through the wall of the uterus which is connected to placenta and the placenta is connected to the fetus through umbilical cord. It is through this the fetus gets food, oxygen and removes wastes like carbon dioxide. Thus there is no direct contact between the circulatory system of the mother and fetus.  

The fetus does not use its own lungs for circulatory system until birth and hence it is different from that of a newborn baby. The fetal circulatory system comprises of blood vessels in the placenta and the umbilical cord, which contains two umbilical arteries and one umbilical vein. As the fetal lungs and liver are underdeveloped, the fetal circulatory system uses two right to left shunts, which are small passages that direct blood that needs to be oxygenated.

The deoxygenated blood from the fetal body enters the right atrium and then to right ventricle. But from right ventricle it bypasses the lungs and flows through the shunt, ductus arteriosus into the descending aorta which is connected to the umbilical artery. This umbilical artery like mentioned above is connected placenta and the deoxygenated blood of fetus reaches the placenta and from there to the mother's circulatory system.

After purification the oxygenated blood from the placenta enters the right atrium from which it flows through another shunt called foramen ovale and then to left atrium. From left atrium it then moves to left ventricle and finally to aorta . From the aorta, the oxygen-rich blood is sent to the brain, heart muscle itself and to lower body.

This whole system is changed at birth as when the baby is born the umbilical cord gets clamped and this fetal system is stopped. When the baby is exposed to air first time its breaths the air which causes the lung to expand and both the shunts that is ductus arteriosus and the foramen ovale close and the baby's circulation system function like an adult's circulation system.

Thank you!