In which type of blood vessel is the mean linear velocity of a red blood cell the lowest?
The same volume of blood flows through each of the different types of blood vessels each minute. Because the capillaries have the largest cross-sectional area (averaging 2500-5000 cm2), and because the velocity of blood flow is inversely related to cross-sectional area, it is clear that the mean linear velocity of a red blood cell is lowest in the capillaries. Under resting conditions, the mean linear velocity of a red blood cell in the capillaries is 0.3-0.6 mm/sec, whereas, the velocity in the aoa (choice A) is about 200 mm/sec. This low velocity of red blood cells in the capillary network allows plenty of time for oxygen to diffuse to the tissues. The velocity of blood flow is ranked from highest to lowest as follows: aoa > vena cavae > large veins > small aeries > aerioles > small veins > venules > capillaries. This ranking assumes the vena cavae have a larger cross-sectional area than the aoa; however, when the vena cavae are paially collapsed (which occurs often) they have a lower cross-sectional area and a higher velocity of blood flow compared to the aoa.
Aoa and large aeries
Aerioles
Capillaries
Small aeries