Blood Vessel Types and Velocity of Blood Flow
Total cross-sectional area for each of the major blood vessel types is illustrated.  The cross-sectional area of each blood vessel is the space through which blood flows, measured in square centimeters.  The cross-sectional area of the aorta is about 5 cmÂ.  The cross-sectional area of each capillary is much smaller, but there are so many that the total cross-sectional area of all capillaries is much greater (2500 cmÂ) than the cross-sectional area of the aorta.  The line at the bottom of the graph shows that blood velocity drops dramatically in arterioles, capillaries, and venules.  As the total cross-sectional area increases the velocity of blood flow decreases.