Because the flow speed in your capillaries is much less than in the aorta, the total cross-section area of the capillaries considered together must be much larger than that of the aorta. Given the flow speeds noted, the total area of the capillaries considered together is equivalent to the cross-section area of a single vessel of approximately what diameter?

A. \(25 \mathrm{~cm}\)

B. \(50 \mathrm{~cm}\)

C. \(75 \mathrm{~cm}\)

D. \(100 \mathrm{~cm}\)

The blood pressure at your heart is approximately \(100 \mathrm{~mm} \mathrm{Hg}\). As blood is pumped from the left ventricle of your heart, it flows through the aorta, a single large blood vessel with a diameter of about \(2.5 \mathrm{~cm}\). The speed of blood flow in the aorta is about \(60 \mathrm{~cm} / \mathrm{s}\). Any change in pressure as blood flows in the aorta is due to the change in height: the vessel is large enough that viscous drag is not a major factor. As the blood moves through the circulatory system, it flows into successively smaller and smaller blood vessels until it reaches the capillaries. Blood flows in the capillaries at the much lower speed of approximately \(0.7 \mathrm{~mm} / \mathrm{s}\). The diameter of capillaries and other small blood vessels is so small that viscous drag is a major factor.