The heart's overcoming capillary viscosity

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Discussion Overview

The discussion centers on how the human heart manages to propel blood through the extensive network of capillaries, particularly focusing on the role of capillary viscosity and the mechanics involved in blood flow through narrow vessels. The conversation touches on aspects of physiology, fluid dynamics, and the distribution of force within the circulatory system.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the capillaries contribute significantly to the impulse needed to move blood through the circulatory system.
  • Another participant suggests that a rheologist and a biologist would be necessary to adequately address the question, emphasizing the distribution of force across numerous blood vessels.
  • It is noted that capillaries lack muscles and therefore do not provide impulse, while veins have structures to prevent backflow.
  • Concerns are raised about the viscosity of blood, with one participant suggesting that the primary issue may be the squeezing of red blood cells through small capillaries rather than viscosity itself.
  • A participant mentions their source for the estimate of capillary length and introduces the concept of the Reynolds number, linking it to fluid dynamics in relation to viscosity and flow characteristics.

Areas of Agreement / Disagreement

Participants express differing views on the role of capillaries in blood propulsion and the nature of blood viscosity. There is no consensus on the contributions of capillaries versus the heart's role in blood flow.

Contextual Notes

Participants reference varying sources for their claims, and there are unresolved questions regarding the accuracy of the capillary length estimate and the implications of viscosity on blood flow dynamics.

Who May Find This Useful

This discussion may be of interest to those studying cardiovascular physiology, fluid dynamics, or anyone curious about the mechanics of blood circulation.

Loren Booda
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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?
 
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Maybe I should have posted this in the Physics Forum?
 
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 :)
 
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.
 

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