Final answer:
The foramen ovale is an opening that allows blood to flow from the right atrium to the left atrium, whereas the ductus venosus allows oxygen-rich blood from the umbilical vein to bypass the liver. Considering the options provided, the correct answer is that the right atrium contains both oxygen-rich and oxygen-poor blood.
Step-by-step explanation:
Understanding Fetal Circulation
An ultrasound that shows normal fetal circulation indicates various special structures are functional in directing blood flow in a fetus. One important structure is the foramen ovale, which is an opening in the interatrial septum that allows blood to flow directly from the right atrium to the left atrium, thus bypassing the fetal lungs, which are not yet functioning. Another key structure is the ductus venosus, which allows oxygen-rich blood from the umbilical vein to bypass the fetal liver and enter the inferior vena cava, mixing with oxygen-poor blood that is returning to the heart.
Considering the options, the correct interpretation in relation to normal fetal circulation is that the right atrium contains both oxygen-rich and oxygen-poor blood (Option 3). This is because the right atrium receives oxygen-rich blood from the umbilical vein through the ductus venosus, and it also receives oxygen-poor blood from the rest of the fetus. The other statements provided are incorrect: the foramen ovale is not a hole between the ventricles but rather between the atria (Option 1), the umbilical vein actually contains oxygen-rich blood (Option 2), and the ductus venosus connects the umbilical vein to the inferior vena cava, not the aorta and pulmonary artery (Option 4).