In reply to a very reasonable point made earlier in the thread ( quote immediately below ) I have included two quotes from a recent paper ,S Magder et al 2016 (1) .


Now, at the same time that the venous return is inhibited by centrifugal or impact effects, the arterial flow (which is downward) would be assisted, and help push blood into the veins from below. So you might question whether overall there is a hindrance of venous return.

From anatomy labs, I remember that veins have a larger cross section than arteries, so more blood mass in the veins, so I suspect you are still correct about venous return being hindered by centrifugal and impact effects."


"A useful analogy for understanding the importance of the large compliance in veins and venules, and why the pressure produced by the heart is not important for the return of blood, is that of a bathtub [
16]. The rate of emptying of a bathtub is dependent upon the height of water above the opening at the bottom of the tub. The height of water creates a hydrostatic pressure due to the mass of the water and the force of gravity on its mass, which pushes the water through the resistance draining the tub. However, the flow out of the tub is not affected by the pressure coming out of the tap."


"The same is true in the circulation. Arterial pressure flowing into veins and venules does not affect the flow out of the veins. "

Volume and its relationship to cardiac output and venous return ...

by S Magder - ‎2016 - ‎Cited by 44 - ‎Related articles
10 Sep 2016 - Changes in cardiac output without changes in stressed volume occur because of changes in arterial and venous resistances which redistribute ...