24.38: Fetal Circulation
Fetal circulation is a unique system that facilitates the exchange of gases, nutrients, and waste products between the developing fetus and the mother. This intricate process takes place through a special organ called the placenta.
Two umbilical arteries transport blood from the fetus to the placenta. At the placenta, the blood absorbs oxygen and nutrients while simultaneously eliminating waste products. This oxygen-enriched and nutrient-rich blood then returns to the fetus through one umbilical vein. The umbilical vein branches into two key parts: the fetal hepatic portal vein and the ductus venosus.
The hepatic portal vein serves the critical function of supplying the liver, while the ductus venosus connects to the inferior vena cava. In the inferior vena cava, the oxygenated blood mixes with deoxygenated blood from the lower half of the fetus's body.
Meanwhile, the superior vena cava collects blood from the upper body and, together with the inferior vena cava, feeds into the right atrium. The foramen ovale, a vital fetal structure, allows most of this blood to bypass the unutilized fetal lungs, moving from the right atrium directly into the left atrium and then into the aorta.
A small fraction of the blood in the right ventricle enters the pulmonary trunk. However, it is redirected through another essential structure, the ductus arteriosus, towards the aorta. The blood circulating in the aorta supplies all fetal tissues via systemic circulation. This efficient and specialized mechanism ensures the optimal growth and development of the fetus.
