(06.05 MC) What is the correct order of blood flow from the heart to the lungs in the fetal circulatory system? a. Ductus venosus, heart, vena cava, ductus arteriosus, arteries b. Vena cava, ductus venosus, heart, ductus arteriosus, arteries c. Ductus venosus, vena cava, heart, ductus arteriosus, arteries d. Vena cava, heart, ductus venosus, ductus arteriosus, arteries

c. Ductus venosus, vena cava, heart, ductus arteriosus, arteries

Explanation:

The circulatory system consists of the heart and blood vessels. In a fetus, the circulation of blood is different from circulation after delivery largely due to the fact that the lungs are not in use, rather, the fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord.

Blood from the placenta is carried to the fetus by the umbilical vein. While some of this blood enters the fetal ductus venosus and is carried to the inferior vena cava, some others enter the liver. The blood from the inferior vena cava then moves into the right atrium of the heart. The foramen ovale, an opening between the right and left atrium in the fetus directs most of the blood flow from the right into the left atrium, thereby, bypassing pulmonary circulation. Most of the blood from the right atrium flows into the left ventricle and is pumped through the aorta to the rest of the body.  

Some of the blood from the right atrium however, enters into the right ventricle and is pumped into the pulmonary artery. The ductus arteriosus which is a special connection between the pulmonary artery and the aorta in a fetus, directs most of this blood away from the lungs and into the arteries.

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