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I have been looking into relative size/volume/surface area of the circulatory system in different species e.g. mouse & man. The only estimates that I could find all quote the same number (60,000 miles) without a primary reference or a plausible way of estimation. This leads me to believe that this is likely to be an urban myth, even though I can imagine the numbers could be quite high.

An adult human has been estimated to have some 60,000 miles (96,560 km) of capillaries with a total surface area of some 800–1000 m2 (an area greater than three tennis courts).

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What is wrong with the last reference? What type of evidence would convince you? –  nico Mar 29 '13 at 19:09
    
Anyway, this page has some good (I think, did not REALLY go through them!) refs/calculations fractalfoundation.org/OFC/OFC-1-3.html –  nico Mar 29 '13 at 19:22
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I strung mine out ones and was only able to get 56k miles... but there may have been some shrinking due to water loss! –  Chad Mar 29 '13 at 19:40

2 Answers 2

Yes, approximately.

Cabin, Henry S., The Heart and Circulation. 1992

Stretched end to end, the vessels of the circulatory system-arteries, arterioles, capillaries, venules, and veins-would measure about 60,000 miles.

Jones, Robert T., Blood Flow. Annual Review of Fluid Mechanics. Vol 1. 1969. 223-244.

According to Zweifach the collective length of capillaries in the human body amounts to about 60,000 miles. (Internal reference removed)

Zweifach, B.W., "The Microcirculation of the Blood". Scientific American. Volume 200, Issue 1. 1959

The total length of the capillaries in the body is almost 60,000 miles.

Loe, Matthew J. and Edwards, William D. "A light-hearted look at a lion-hearted organ (or, a perspective from three standard deviations beyond the norm) Part 1 (of two parts)". Cardiovascular Pathology. Volume 13, Issue 5, September–October 2004, Pages 282–292.

The blood vessels (arteries, capillaries, and veins), laid end-to-end, would measure about 100,000 km (60,000 miles), or approximately 2.5 times the circumference of the earth.

Capillaries account for about 80,000 km (50,000 miles) of vasculature in an adult.

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Do any of these references do the calculation based on empirical data, or are they all just repeats of the claim? –  Oddthinking Jun 7 '13 at 23:17
    
They are repeats that have been accepted by the peer-review process (except for the first one). The fact that the Loe and Edwards reference doesn't quote the 60,000 miles of capillaries claim, but refines it to be 60,000 miles of vessels, 50,000 of which are capillaries, means they put some independent thought into the numbers they used. –  Articuno Jun 7 '13 at 23:21
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If they are unreferenced claims, without supporting, reproducible empirical evidence, we can't use our magic skeptical powers to check on it... even if they passed initial peer-review. The OP already dismissed a peer-reviewed claim that doesn't have references to support their claim (although at least has the decency to have a range: 60,000-100,000 miles). –  Oddthinking Jun 8 '13 at 0:10

It's probably just an estimate, but is reasonable given other physiological data available.

According to this chart, a 50th percentile, middle age man is about 180lb (80kg). From Harvard's bio numbers, the weight of a skeleton, is typically about 15% of a person's weight. This leaves us with about 150lb (70kg) of tissue to be filled with blood vessels.

This well referenced article shows that the tissues remaining all have densities of approximately 1g/cm^3.

If you take the 60,000mi value at face value, you could calculate the upper limit (because your mass is not 100% blood vessels) for the average diameter of a blood vessel by the following equation:

(1 g/cm^3) (100,000 km) (pi/4 d^2) = (70 kg) d = sqrt( (70kg) / ((100,000 km) (pi/4) (1 g/cm^3 )) ) d = 30 microns

According to the University of Minnesota's page on vascular physiology, capillaries are the most numerous, make up much of the length of the vascular system, and average 5-10 microns in diameter.

Since the plausible upper limit on average blood vessel diameter is 30 microns, it seems reasonable that there could 60,000 miles of blood vessels in the human body when capillaries will try to pull that average toward 5-10 microns.

I'd also like to point out the wide range you're likely to see in real life. The University of Minnesota page, for instance, figures there's about 25,000 miles of capillaries. I suspect there are large error bars but that the estimate is roughly correct.

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Downvoter care to explain? I know about our policy toward theoretical answers, but this really isn't theoretical just because it includes a calculation. I've just established that there's enough room in the human body for that length of vessels given how big they actually are. –  William Grobman Jul 10 at 21:20

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