When a baby is developing maternal blood supplies the oxygen, blood, and nutrients to the fetus and takes away the waste. The exchange of maternal blood and fetal blood to the fetus happens through the placental membrane and the umbilical cord vessels. The umbilical vein goes into the body through the umbilical ring, and half of the blood running though it goes to the liver and the rest goes to the ductus venous. It joins with the inferior vena cava. Blood goes to the fetal right atrium from the inferior vena cava. From there, most blood goes through the foramen ovale into the left atrium. The rest of the blood that enters the right atrium comes from the superior vena cava, goes to the right ventricle, and out of the pulmonary trunk. Since the lungs are collapsed only a very small amount goes to them. Blood from the inferior vena cave bypasses the lungs through the ductus arteriosus which connects to the descending part of the aortic arch. Blood with low oxygen going to the superior vena cava bypasses the lungs and does not go ingo the part of the aorta that goes to the heart and brain. The higher oxygen concentrated blood goes to the left ventricle and is pumped to the aorta where some reaches the myocardium and some reaches the brain. When blood comes from the descending aorta it has the les oxygenated blood from the ductus arteriosus. Some of that blood is taken to the lower regions of the body from branches off the aorta. The remaining blood goes through the umbilical arteries. They branch from the internal iliac arteries and lead to the placenta then the blood is re-oxygenated. The umbilical cord has two arteries and one vein.
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