The Body: A Guide for Occupants

by Bill Bryson

The three phases of the process are respiration, phonation, and articulation.

For many, the stammering miraculously ceases when they sing the words or speak another language or talk to themselves.

it is more centrally located in the chest than that.

The heart has no time for distractions. It is the most single-minded thing within you. It has just one job to do, and it does it supremely well: it beats. Slightly more than once every second,

rhythmically pulses to push blood through your body—and these aren’t gentle thrusts. They are jolts powerful enough to send blood spurting up to three meters if the aorta is severed.

The heart is not really one pump but two: one that sends blood to the lungs and one that sends it around the body.

the brain takes 15 percent, but actually the greatest amount, 20 percent, goes to the kidneys.

Curiously, the blood passing through the chambers of the heart does nothing for the heart itself.

The two phases of a heartbeat are known as the systole (when the heart contracts and pushes blood out into the body) and diastole (when it relaxes and refills). The difference between these two is your blood pressure.

say 120/80, or “120 over 80” when spoken—simply measure the highest and lowest pressures your blood vessels experience with each heartbeat. The first, higher number is the systolic pressure; the second, the diastolic.

Every time you stand up, roughly a pint and a half of your blood tries to drain downward, and your body has to somehow overcome the dead pull of gravity. To manage this, your veins contain valves that stop blood from flowing backward, and the muscles in your legs act as pumps when they contract, helping blood in the lower body get back to the heart.

blood pressure isn’t a fixed figure, but changes from one part of the body to another, and across the body as a whole throughout the day.

No two heart attacks are quite the same, it seems. Women and men have heart attacks in different ways.

By one estimate, a single drop of blood may contain four thousand different types of molecules. That’s why doctors are so fond of blood tests: your blood is positively packed with information.

A notable paradox of red blood cells is that although they carry oxygen to all the other cells of the body, they don’t use oxygen themselves. They use glucose for their own energy needs.

Although everybody reads and pronounces the last group as the letter O, Landsteiner in fact meant it to be taken as a zero, because it didn’t clump at all.

Rh factor—short for “rhesus,” from the type of monkey in which it was found.

People with O blood, for instance, are more resistant to malaria but less resistant to cholera.

“Blood is a living tissue,”

Most of us think of blood as being more or less equally distributed around the body at all times. Whatever amount is in your arm now is what is always there. In fact, Doctor explained to me, it is not like that at all. “If you are sitting down, you don’t need so much blood in your legs because there is not a great requirement for oxygen in the tissues. But if you leap up and start running, you are going to need a lot more blood there very quickly. Your red blood cells, using nitric oxide as their signaling molecule, in large part determine where to dispatch blood as the body’s requirements change from moment to moment. Transfused blood confuses the signaling system. It impedes function.”

In the meantime, it remains a slightly humbling reflection that about a million times per second our bodies do something that all the science of the world put together so far cannot do at all.

3 If our blood is red, incidentally, why do our veins look blue? It is simply a quirk of optics. When light lands on our skin, a higher proportion of the red spectrum is absorbed, but more of the blue light is bounced back, so blue is what we see. Color is not some innate feature that radiates out of an object but rather a marker of the light bouncing off it.

For a long time, endocrinologists thought that testosterone was exclusively a male hormone and estrogen exclusively female, but in fact men and women produce and use both.

It is disproportionately large in infants, which is why their bellies are so delightfully rounded.

Altogether the liver takes part in some five hundred metabolic processes. It is essentially the body’s laboratory. Right now, about a quarter of all your blood is in your liver.

Perhaps the most wondrous feature of the liver is its capacity to regenerate.

The liver was long thought to be the seat of courage, which is why a cowardly person was deemed “lily-livered.”

The spleen is roughly the size of your fist, weighs half a pound, and sits fairly high up on the left side of your chest. It does important work monitoring the condition of circulating blood cells and dispatching white blood cells to fight infections. It also acts as a reservoir for blood so that more can be supplied to muscles when suddenly needed, and it aids the immune system.

Giraffes, oddly, sometimes have gallbladders and sometimes don’t.

It remains something of a mystery even now as to why we have two kidneys. It is splendid to have a backup, of course, but we don’t get two hearts or livers or brains, so why we have a surplus kidney is a happy imponderable.

It is slightly mortifying to realize that the only raw flesh we normally see is the meat of animals that we are about to cook and eat. The flesh of a human arm, once the outer skin is removed, looks surprisingly like chicken or turkey. It’s only when you see that it ends in a hand with fingers and fingernails that you realize it’s human. This is when you think you might be sick.

“You shouldn’t ever try to kill yourself by cutting your wrists, by the way,” he says. “All of those things going in are wrapped in a protective band called a fascial sheath, which makes it really hard to get to the arteries. Most people who cut their wrists fail to kill themselves, which is no doubt a good thing.”

“It’s also really hard to kill yourself by jumping from a height,” he adds. “The legs become a kind of crumple zone. You can make a real mess of yourself, but you are very likely to survive. Killing yourself is actually difficult. We are designed not to die.”

It is usually said that we have 206 bones, but the actual number can vary a bit between people.

Our bones do a lot more than keep us from collapsing. As well as providing support, they protect our interiors, manufacture blood cells, store chemicals, transmit sound (in the middle ear), and even possibly bolster our memory and buoy our spirits thanks to the recently discovered hormone osteocalcin.

The most fundamental element of bone is collagen.

Collagen makes the white of the eye but also the transparent cornea.

In muscle it forms fibers that behave just like rope in that they are strong when stretched but collapse when pushed together.

“The bone in a professional tennis player’s serving arm may be 30 percent thicker than in his other arm,”

Because of the way they are constructed, bones are, to an extraordinary degree, both strong and light.

“Bone is also the only tissue in the body that doesn’t scar,”

Even more remarkably, bone will grow back and fill a void. “You can take up to thirty centimeters of bone out of a leg, and with an external frame and a kind of stretcher you can have it grow back,” Ben says. “Nothing else in the body will do that.” Bone, in short, is amazingly dynamic.

You also need lots of muscle and a judicious assortment of tendons, ligaments, and cartilage.

What's the difference ?

Tendons and ligaments are connective tissues.

Tendons connect muscles to bone;

ligaments connect bon...

Tendons are stretchy; ligaments, less so. Tendons are essentially e...

That at least is better than cartilage, which has no blood supply at all and therefore almost no capacity to heal.

It takes one hundred muscles just to get us to stand up. You need a dozen to move your eyes over the words you are reading now.

On a computer keyboard you strike the keys with the tips of your fingers but with the side of your thumb.