The Misconception of Our Vessels

[Zaetus]

Hello, I do not post much here for obvious reasons, however I want to ask a question about this misconception of our vessels (or perhaps a fact if someone can share some insight on this).

 

All my life, I have been hearing over and over again about how our blood vessels are large enough to circle the world twice. I heard it first in 6th grade, and many times after. Today, after viewing a human dissection video, the surgeon mentioned it also.

 

I find this impossible to believe. Would anyone care to explain to me exactly why this is? Or how did this notion come to be?

 

I asked my anatomy professor, and he didn't understand my question and instead told me not to believe everything I read on the internet (lol funny guy). However, he told me that the alveoli in our lungs are compacted so tightly they their total surface area can be spread across a football field.

 

It boggles my mind every time I hear this.

[CaptainPanic]

You have a couple of very large blood vessels. You have far more smaller ones, like the ones visible in your hand. However, you have even more really tiny blood vessels, called 'capilaries'. And you really have a lot of those. Here's a wikipedia picture of how the system is built.

 

But let's start with the comment about the lungs. Your lungs are typically about 5 liters in volume. If that was a single bag of air, its surface area would only be about 0.14 m2 (I made a quick calculation assuming it would be a sphere). Now imagine that instead they were 10 bags of each 0.5 liters. Individually those would all have a surface area of 0.03 m2, but in total it would be 0.30 m2, which is a little more than double the surface area, but still the same total volume.

 

In reality, you have (according to wikipedia) 700 million little bags. If those were spheres, I calculate their total surface area would be 125 m2. Wikipedia puts it at 70 m2 (in the previous link). That's not exactly a football field... but it is still quite huge.

 

Now imagine a surface of 70 m2, covered in tiny little blood vessels. Going up and down (and also from right to left), one vessel every fraction of a millimeter. I hope you can see we are rapidly reaching a very large number?

 

And then you should realize that your whole body is filled with such little blood vessels. Your muscles have them. Your internal organs have them. Your brain has them. Etc, etc.