You are explicitly envisioning the circulatory system as one long thin tube - 128,000 km long by 8 microns in diameter - through which all the blood must be pushed with every circulation. That isn't how it works. The system starts out with a single thick vessel which branches eventually into a complex mesh of up to 10 billion capillaries, each about 600 microns in length.
As someone who has worked with hydraulic systems I am aware of this issue – I did not bring it up because I do not want to get too technical.
However now you have mentioned it:
What you are saying is that the heart’s hydraulic system would be more efficient because it divides the blood flow from the arteries into lots of capillaries – rather than pushing the blood through 128,000 klms of a single very long capillary. This is of course true; and I certainly never said the capillaries were joined end to end – only that their total length was 128.000 klms.
The problem for your argument is that every time you divide the flow in a pressurised pipe you divide the pressure; (i.e. if you have 10 psi in a pipe and you divide the flow into 2 pipes of equal size – you then only have 5 psi in each pipe).
If you divide the pressure in our arteries into 10 billion capillaries you are dividing that pressure by 10 billion – giving you zero pressure.
There are other issues concerning volume of capillaries as compared to volume of arteries. These issues relate to potential pressure in capillaries and flow rate etc.. I have not done these calculations and do not intend to. For, as any sane mechanical engineer will tell you, our cardiovascular system is not reliant on pressure build-up from the heart.
Edited 1 time(s). Last edit at 11-Feb-20 09:09 by Robert Jameson.