To understand the fetal blood circulation, we need to arrange the vessels in the correct sequence. The circulation starts when oxygenated blood from the placenta travels through the umbilical vein. From the umbilical vein, the blood then enters the ductus venosus, which allows most of the blood to bypass the liver and flow directly into the inferior vena cava.
Next, the oxygen-rich blood from the inferior vena cava enters the right atrium of the heart. During fetal circulation, some of this blood will flow into the right ventricle, but a significant portion is diverted to the left atrium through a small opening called the foramen ovale. This diversion ensures that the oxygenated blood is delivered primarily to the left side of the heart and then out to the body.
From the left atrium, the blood moves into the left ventricle, where it is then pumped into the aorta and distributed to the body. It’s important to remember that while some blood is pumped to the lungs for oxygenation via the right ventricle and pulmonary artery, the lungs are not functional in the same way as after birth; therefore, most blood bypasses them.
Finally, after delivering oxygen to the body, deoxygenated blood returns through the umbilical arteries back to the placenta, where it will be re-oxygenated. In summary, the sequence of vessels in the fetal blood circulation is:
- umbilical vein
- ductus venosus
- inferior vena cava
- right atrium
- foramen ovale
- left atrium
- left ventricle
- aorta
- umbilical arteries