From the moment of birth, our heart supplies the oxygen-poor blood from the hollow veins into the pulmonary arteries that lead to the lungs.
In the lungs, the same blood is charged with oxygen and returns to the heart, through the pulmonary veins, in order to be distributed in the various organs and tissues of the body after the introduction into the aorta.
But if this occurs only at birth, how does the oxygenation of the blood and its distribution to the tissues take place before then?
As long as we are in the womb, we do not have the possibility to breathe (and to oxygenate the blood), therefore it is our mother who supplies us with oxygenated blood.
That's how…
The maternal blood rich in oxygen reaches our body through the umbilical vein, which pours its contents into the inferior vena cava with which it is connected.
The inferior vena cava ends, as usual, in the right atrium, therefore it will have that the oxygenated blood reaches the heart through a different way from the "canonical" one mentioned above.
Once inside the right atrium, oxygen-rich blood flows only minimally into the right ventricle, as it takes up a small opening in between, located between the right atrium and the left atrium and called the Botallo hole .
With the direct passage from the right atrium to the left atrium, the oxygenated blood is already ready to enter the aorta and, from there, be distributed in the various organs of the body.
The answer is: they mix and take the pulmonary artery, which, however, presents a deviation - called arterial duct - which puts it in direct communication with the aorta. As a result, the blood reaching the right ventricle is also sorted, in one way or another, into the main arterial system of our body.
