Which of the following would be expected to have the HIGHEST oxygen content?
a) the fetal carotid arteries
b) the fetal umbilical arteries
c) the fetal internal jugular veins
d) the fetal ductus venosus
e) the fetal descending aorta
Answer d.
Among the fetal vessels, the highest oxygen saturation would be expected in the umbilical vein and its continuation as the ductus venosus; this vessel contains blood with a high oxygen saturation directly into the IVC. On arrival to the right atrium, this blood is preferentially shunted through the foramen ovale into the left atrium, then left ventricle, and subsequently in the ascending aorta and cerebral circulation. Although this arrangement results in increased oxygen delivery in the cerebral circulation compared to the descending aorta, the oxygen content of the cerebral vessels is still lower than that of the ductus venosus. This is explained by mixing at the right atrial (with blood from the SVC), left atrial (with blood from the pulmonary veins), and aortic (with blood from the ductus arteriosus) levels.