Fetal circulation

The fetus receives everything it needs for development from the mother's blood. Maternal blood enters the placenta ("baby's place") through the uterine artery. The blood of the mother and fetus do not mix in the placenta, which is why the fetus's circulation is called placental. In the placenta, the fetus's blood receives nutrients from the mother's blood through the hematoplacental barrier. From the placenta, arterial blood enters the umbilical vein of the fetus, which, as part of the umbilical cord, goes to the lower edge of the liver, lies in the groove of the umbilical vein and divides into two branches at the level of the porta hepatis. The first branch flows into the portal vein, and the second branch - the venous (Arantius) duct (ductus venosus) - into one of the hepatic veins or into the inferior vena cava. Thus, the arterial blood that flows through the umbilical vein from the placenta, partly enters directly into the inferior vena cava, and partly into the liver, which is the organ of hematopoiesis in the fetus. Then, through the hepatic veins, the blood enters the inferior vena cava, where it mixes with venous blood flowing from the lower part of the fetus's body. Through the inferior vena cava, the mixed blood enters the right atrium. From this median, through the oval opening of the interatrial septum, the blood enters the left atrium, where its flow is directed by the valve of the inferior vena cava (Eustachian valve), which is clearly developed in the fetus. From the left atrium, the blood enters the left ventricle, and then through the aorta and the arteries branching off from it, it is directed to the organs and tissues of the fetus's body.

Venous blood from the upper part of the fetus's body enters the right atrium via the superior vena cava. Through the right atrioventricular orifice, this venous blood passes into the right ventricle. From the ventricle, the blood is directed into the pulmonary trunk, and then flows through the large arterial (Botallo's) duct (ductus arteriosus) directly into the aorta (below the branching off of the left subclavian artery). In the aorta, new portions of venous blood from the right ventricle are added to the mixed blood that has entered from the left ventricle. This mixed blood flows out through the branches of the descending aorta to all the organs and walls of the lower half of the fetus's body. Thus, the upper half of the fetal body (in particular, the brain), which is supplied with blood by branches of the aortic arch that extend from it before the arterial duct enters (the common carotid and subclavian arteries), receives blood that is richer in oxygen and nutrients than the lower half.

The enrichment of the fetal blood with oxygen and nutrients occurs in the placenta, where mixed blood from the aorta flows through the internal iliac arteries, and then along its branches - the paired umbilical artery - into the placenta.

After birth, significant changes occur in the vascular system of the newborn. Placental circulation is abruptly replaced by pulmonary circulation. The lungs, pulmonary arteries and veins begin to function. The umbilical vessels, ligated after birth, become empty: the trunk of the umbilical vein turns into the round ligament of the liver, and the umbilical arteries - into the right and left lateral umbilical ligaments; the lumen of the arteries is preserved only in their initial section. These umbilical ligaments are located on the posterior surface of the anterior abdominal wall. The venous duct turns into a venous ligament; the arterial duct, which in the fetus connected the pulmonary trunk with the concave part of the aortic arch, becomes an arterial ligament connecting the trunk (or left pulmonary artery) with the aortic arch.

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