The bypass circuit of an unborn child
In the unborn child, the fetus, there are special features of the cardiovascular system. This is known as the fetal circulation or bypass circulation. This is necessary because the lungs of the unborn child are not yet unfolded, i.e. the pulmonary circulation is not yet functioning as in adults.
Oxygen-rich blood is supplied to the baby by the mother via the umbilical vein, which is connected to the placenta. This runs as the so-called “ductus venosus Arantii” into the inferior vena cava and bypasses the portal system. In the heart there is a right-left shunt in the fetus.
The blood flows from the right heart, bypassing the pulmonary circulation, via the “foramen ovale” directly into the left heart and from here it is pumped into the body’s circulation. The fetus finally releases its blood through the umbilical artery back to the placenta. After birth, the lungs unfold and the pulmonary circulation opens. This results in altered pressures and various connections of the bypass circulation are passively closed.