The heart's overcoming capillary viscosity

[Loren Booda]

The human heart is able to power viscous blood through ~100,000 miles of narrow capillaries in less than a minute. Do the capillaries themselves provide a substantial fraction of the needed impulse?

[Loren Booda]

Maybe I should have posted this in the Physics Forum?

[Monique]

You need a rheologist to answer this question and a biologist :) First of all, where do you get your numbers of 100,000 miles of narrow capillaries per minute?

Basically you are asking how the force is distributed over all those bloodvessels, since it is distributed over so many vessels you'd expect the pressure in cappillaries to be too low.

Well, capillaries don't have muscles so they don't provide any impuls. But veins DO have structures that prevent the blood from flowing in the wrong direction.

I don't think blood is really viscous either, the main problem would be squizing the red blood cells through the small capillaries.

Basically the heart is just displacing the blood a little at a time and this pushes the blood forward.

That is the best I can give :P sorry :)

[Loren Booda]

Monique,

The milage estimate I memorized from the ~1965 Worldbook Encyclopedia as a kid! I also consider blood products to a major source of viscosity. Remember that the Reynolds number (characteristic of turbulence) increases as the viscosity and fluid velocity, and reciprocally to its perpendicular cross-section.