Which structure carries oxygen into the intervillous space of the placenta?

The structure that carries oxygen into the intervillous space of the placenta is the spiral arteries. These arteries, which arise from the uterine arteries, supply oxygen-rich blood from the maternal circulation directly to the intervillous space, where it bathes the chorionic villi. The chorionic villi then facilitate the exchange of gases and nutrients between maternal blood and fetal blood.

In the context of placental anatomy and physiology, it is crucial to understand that the spiral arteries undergo significant remodeling during pregnancy to increase blood flow and ensure adequate oxygen delivery to the fetus. This enhanced blood flow is fundamental for proper fetal development, as it allows for sufficient oxygen and nutrient transfer.

While the umbilical cord is essential for transporting oxygen and nutrients between the fetus and placenta, it does not carry oxygen into the intervillous space itself. The chorionic villi are responsible for the actual exchange of gases and nutrients at the placental interface, but the oxygen-rich maternal blood is delivered to this space by the spiral arteries. Maternal veins are responsible for returning deoxygenated blood back to the maternal circulation; they do not facilitate the delivery of oxygen to the placenta.