Fetal Circulation

April 9, 2009. The fetal circulation begins at the placenta. The placenta moves blood to the fetus via the umbilical vein. ½ of this blood enters the ductus venosus, a shunting vessel that moves 80% of the blood directly into the inferior vena cava. The other ½ of blood enters the liver through the umbilical vein into the right lobe of the liver. The umbilical vein joins with the portal vein of the liver the blood is moved to the right atrium of the heart. From the right atrium some of the blood flows through an opening, the foramen ovale, between the right and left atrium. From the left atrium blood moves to the left ventricle up through the aorta and out into the body. Some of the blood moves from the aorta to the internal iliac arteries, and out through the umbilical arteries where it re-enters the placenta. From the placenta the carbon dioxide and waste are taken up by the mothers circulation for elimination. Some of the blood from the right atrium does not go through the foramen ovale it enters the right ventricle and is pumped into the pulmonary artery where a special connection, ductus arteriosus between pulmonary artery and aorta, directs blood away from the lungs. The lungs are not in use because the fetus is suspended in fluid, oxygen is supplied through the umbilical cord. The foramen ovale in a fetus has a flap of tissue over it that becomes fossa ovalis which becomes a thicken membrane of the right atrium in adults. The ductus arteriosus of a fetus closes after birth and becomes ligamentum venosum. The ductus venosus of a fetus becomes ligamentum venosum after birth.
Being a mother I never really knew the fetal circulation pathways. It is amazing how our body produces these shunting vessels needed during fetal development to transport blood to areas thus bypassing the pulmonary circuit which is there just waiting to be used after birth. Once the fetus has been born and it takes a breath signaling the pulmonary circuit to kick in, the body knows to close the vessels and they become a membrane and ligaments. Human body amazement.