There are approximately 100,000 miles of blood vessels in an adult human body -- enough to circle the planet four times. The arteries and veins are an intricate network that helps the organs get the nutrients they need. Veins are fragile and can collapse easily under certain circumstances. Arteries, on the other hand, are sturdier and thicker as they are built for the heavy workload. While these two types of vessels are similar, the key differences in their designs make the circulatory system one of the most efficient superhighways.
For the most part, oxygenated blood is carried away from the heart by the arteries, while the veins carry deoxygenated blood back to the heart. The one exception to this rule is pulmonary and umbilical blood flows. From the heart's right ventricle, deoxygenated blood travels to the lungs via the pulmonary artery. With the help of capillaries, the blood oxygenates through the respiration process and is returned to the heart via the pulmonary veins. In pregnancy, the artery passes deoxygenated blood to the placenta, and the umbilical vein inside the cord carries oxygenated blood back to the fetus.
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