You have accepted a part-time tutoring job for first-year medical students. One of your students asks if you would please clarify the details of normal fetal circulation. Which of the following best describes the path of the majority of the blood that enters the right atrium?A. RA > foramen ovale > LA > LV > systemic circulationB. RA > RV > VSD > LV > systemic circulationC. RA > RV > pulmonary circulation > LA > LV > systemic circulationD. RA > RV > ductus arteriosus > LV > systemic circulatioE. RA > RV > ductus arteriosus > systemic circulation

A

Explanation:

In the normal fetal circulation, oxygenated blood is flows from the placenta to the liver through the umbilical vein. From the liver it flows through the ductus venosus and portal sinus to the inferior Vena Cava and then into the right atrium.

From the right atrium, majority of the blood pass through the foramen ovale into the left atrium. The foramen ovale is a small opening in the wall between the right atrium and the left atrium. It is a normal anatomical structure in fetuses which allows oxygenated blood to bypass the pulmonary circulation as the fetus is not yet getting oxygenated blood from the lungs. The foramen ovale closes at birth when the lungs become functional.

From the left atrium, the blood flows into the left ventricle and into the aorta for systemic circulation. A small amount goes through the pulmonary vessels to the lungs.