### Author Topic: Playing the numbers game  (Read 1725 times)

#### shvarz

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##### Playing the numbers game
« on: March 31, 2006, 02:03:27 PM »
Sometimes it's fun to put things in perspective by converting stuff to "dogs years".

For example, I just found out the approximate size of surface area of our bodies.  And it's not several square meters, as you might think at first.  It is a lot more, because we should include all the area that is exposed to the "outside" and that includes our digestive system, lungs and urinal tract.  Add all this together and you get 400 square meters.  That's about the size of two basketball courts!!!

Pretty impressive on it's own, but let's look at it from the point of view of a cell of an immune system, which has to protect all this area from incoming bacteria and viruses.
First, let's conert this flat area to a sphere.  That will make a sphere with radius of 5.6 meters.  The size of an immune cell is 10 micrometers.  Make a proportion to bring the cell to our size and the sphere's radius grows to 5.6x10^7 meters = 56000 km.  That's a little more than twice the radius of Jupiter, the biggest planet in our solar system.

Now a virus to the cell is about as big as a dime to us.  So there is your goal: guard the planet twice as big as jupiter from a constant rain of dimes coming from space.  Sounds like fun, doesn't it?
"Never underestimate the power of stupid things in big numbers" - Serious Sam

#### shvarz

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##### Playing the numbers game
« Reply #1 on: March 31, 2006, 02:21:04 PM »
On the other hand, I forgot to add that there are 10^11 cells of immune system in the body, so if you are one of them, then you get the area of "only" about half of a square km.

On the third hand, most of these 10^11 are not actively guarding (they are on R&R deep inside the body), so in reality you'll get several square km to guard :)
"Never underestimate the power of stupid things in big numbers" - Serious Sam

#### Numsgil

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##### Playing the numbers game
« Reply #2 on: March 31, 2006, 03:39:03 PM »
That's an interesting way of looking at it, though I think I might question several of your basic assumptions.

For instance, Virus's penetration probably isn't uniform for all exposed areas.  Fingers probably get exposed to far more crap (both literally and figuratively) than, say, our nipples.  Our intestines are quite literally a breeding ground for cold causing bacteria.

Second, some areas of skin are quite thick and resiliant to outside infection unless damaged, so the immune system doesn't need to defend these as well as other areas.

Third, since viruses multiply it quickly becomes evident of where an infection is brewing, so the immune system can direct all the members of its immune force special forces.  The infection by comparison could be as large as the Jupiter's Red spot to keep in your analogy.  The body knows it's won when the infection doesn't come back.

#### shvarz

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##### Playing the numbers game
« Reply #3 on: March 31, 2006, 04:13:17 PM »
Quote
Fingers probably get exposed to far more crap (both literally and figuratively) than, say, our nipples...

some areas of skin are quite thick and resiliant to outside infection unless damaged,....

All our "outside" skin is tiny compared to the "inside" skin, so these things should not matter as much.

But you are right, there are multiple ways for protection.  Analogy is never perfect.

Quote
he infection by comparison could be as large as the Jupiter's Red

Yes, but that's a whole different story of what happens if initial defenses fail.  I was just looking at the first level of defense.
"Never underestimate the power of stupid things in big numbers" - Serious Sam