By which of the following routes does blood flow through the umbilical cord between the pla-centa and the fetus?
a. One umbilical vein and one umbilical ar-tery
b. One umbilical vein and two umbilical ar-teries
c. Two umbilical veins and one umbilical ar-tery
d. Two umbilical veins and two umbilical arteries
ANS: B
Maternal blood flows into the intervillous space through the spiral arteries, while fetal blood is supplied to the villi from two umbilical arteries. Oxygenated fetal blood leaves the chorionic villi capillaries through placental venules and returns to the fetus through a single umbilical vein.
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