TEN TRILLION CELLS WALKED INTO A BAR

by PAUL INGRAHAM

Paul Ingraham is a writer and Registered Massage Therapist in downtown Vancouver. At SaveYourself.ca, Mr. Ingraham also waxes poetic and scientific about musculoskeletal health care, publishing dozens of unusual essays, handy tips, and advanced patient tutorials about common injuries and pain problems like muscle strain, low back pain and neck pain, runners injuries like iliotibial band syndrome, and medically neglected problems like muscle knots and trigger points.

You are a colony of (at least) ten trillion cells.¹ That is what a human being is -- a very large social gathering of cells. Ten trillion is a conservative estimate, but it is one heck of a lot of cells. That is about 200,000 times more cells in a single person than there are people on planet Earth. That’s the sort of number that you really can’t get your head around, even if you have a very big head.

SO HOW DO TEN TRILLION CELLS WALK INTO A BAR?

How did they walk, I mean? Or even stand up? It’s a bit of a trick for ten trillion cells to do that. Individually, they certainly couldn’t pull it off. A single cell would have trouble walking six inches for a hot date with another single cell.²

It’s a cooperative effort, obviously. There are probably many committees, subcommittees and review panels involved. But, in spite of the complexity and bureaucracy, the end product -- walking -- is efficient. Walking is so efficient, in fact, that it constitutes one of the great mysteries of how people work. We still can’t make a bipedal robot that can walk, not like us anyway -- “we,” meaning geniuses at MIT studying robotics. We humans simply don’t understand the details of our own locomotion.

But we do have some idea how we at least stay upright. Even I understand it. This superficially simple thing of rising up to a height of six feet or more is an impressive feat for a bunch of cells who are, individually, no taller than a coffee stain. But together they pull it off, and that basic accomplishment is what I’ll focus on here. This is stuff that cells probably learn in cell kindergarten.

YOU AREN'T STACKED

Contrary to popular opinion, bones are not stacked on each other like bricks. We do not really rest on our joints as much as you might think, nor in the way you might think. There is compression and friction in joints due to gravity, but this is not the supportive principle by which we manage to get upright each morning and stay that way.

Vertebrae in particular are not really made for support. We are one of the few creatures on Earth with an upright spine, the odd animal out; all other vertebrates on Earth feature a horizontal spine, which is much more obviously not built for bearing weight by stacking. In fact, the spine we have is really not particularly well-constructed for verticality. It’s as though we borrowed a tool used by other species for hammering nails, and decided, “Let’s use this for screwing in lightbulbs.” It’s a bit queer, really.

In fact, rather than being stacked, we are held together and upright by muscles. Bare skeletons, as a general rule, fall over very easily. In the living body, even when we think that we are completely relaxed, our muscles are actually sustaining a constant level of tension -- called “resting tone” — that holds joints together.³ When we are anaesthetized, surgeons must be cautious not to dislocate joints,⁴ because they become quite loose. This constant tension is what we really stand on -- not bone resting on bone.

This idea, in which the rigid elements of a system float in a continuous tension network, was called “tensegrity” (tension/integrity) by Buckminster Fuller. For a long time the ideas were more widely known among architects than biologists,⁵ but “tensegrity biomechanics” and “biotensegrity” are slowly coming into their own.

Bones float in muscle, functioning more like “spacers” than bricks. They provide rigidity for leverage and serve as foundations for complex arrangements of high-tension wires (muscles and tendons). We are pulled upright, and held upright, in much the same way a circus tent pole is erected and held upright -- not because it is resting on itself, but because it is being pulled equally in all directions by ropes. Unlike a circus tent pole, we actually need to move around, so this arrangement is extremely dynamic and active, constantly at work even when we are sitting.

There is one other major principle that keeps us upright: hydrostatic pressure.

WE ARE MOSTLY BAGS OF WATER

Once again, bones are of secondary importance to another more important substance: soft connective tissue. Some aliens on an episode of Star Trek: The Next Generation referred to humans as “ugly bags of mostly water.” And right they were, at least about the bags and the water. Ugly depends on which bag of water we’re talking about (but let’s not go there).

The point the aliens were trying to make was that humans are mostly water -- and everyone knows that, right? More specifically, and less widely known, is that our water is contained in flexible membranes (bags). The bag, or sack is made of our connective tissue, intricate layers of a substance somewhat like Saran Wrap that literally holds us together. We have more connective tissue than anything else. ⁶

The water (hydro) inside of us is under constant (static) pressure -- hydrostatic pressure. The bag is tight. This is exactly like putting a tight elastic band around a water balloon: it squishes it into a more elongated shape. If you were to put several rubber bands in a row around a water balloon, it would start to look more like a tube than a balloon. In fact, it might start to resemble, say, a leg. If only it could balance itself, this “balloon leg” could stand upright -- thanks to the pressure of the water inside.

This is entirely how plants stand up. Spinach has no spine, no bones at all, but it still manages to stand up. Unless you don’t water it, and then it wilts -- no water, no pressure, no standing up. And of course there is one part of the human body, the male human body specifically, that illustrates this principle -- perfectly.

TA DA!

Our ten trillion cells manage to walk into a bar by applying two major physical principles: tensegrity and hydrostatic pressure. Our cells build tough membranes to tightly surround compartments of pressurized water, they make rigid bones to act as spacers and points of leverage, and they arrange themselves in complex systems of muscle tissue in order to literally pull us into the vertical position and keep us there like a tent pole.

How ten trillion cells order a tall cold one and generate bad pick-up lines is a completely different mystery altogether.

Notes
1. Actually, this number is in the middle of a stunning range of possibilities suggested by experts over the last century. The highest estimate I’ve ever seen, published in 2003 in the popular but credible book A short history of nearly everything , by Bill Bryson, was in the quadrillions — that’s right, quadrillions, as in thousands of trillions! In 2006 in National Geographic, citing various experts, Joel Achenbach reports that microbes living in our bodies outnumber our own cells 10 to 1 and there are a hundred trillion microorganisms in the intestines alone — so those figures would also put the total for the whole organism well into the quadrillions. At the other extreme, estimates of the number of cells we have range as low as tens of billions. But, regardless, we have a lot of cells!

2. If you do the math, “walking” six inches for a cell is like us walking about a mile — not too far for a hot date.

3. There is just one joint in the body that can maintain its integrity after complete muscular dissection: the hip joint. The socket of that joint is so deep and perfectly fitted to the ball of the femur, and the capsule of ligaments around it so sturdy and air tight, that it is held nicely in place by “suction.” However, cut a tiny hole in the capsule with a scalpel, and the joint immediately dislocates!

4. Casey et al. BMJ. 1995.

5. “Tensegrity.” Wikipedia.com.

6. We really do have a lot of connective tissue, but connective tissue also includes some surprising and counterintuitive tissues like blood and fat.