The Body: A Guide for Occupants

by Bill Bryson

Most define fingers as “one of the five terminal members of the hand, or one of the four other than the thumb.” Because of the uncertainty, even doctors do not number fingers, because there is no agreement on which is finger number one.

He discovered that nails driven through the palm of the hand—the method traditionally depicted in paintings—would not support the weight of a body. The hands would literally tear apart. But if the nails were driven through the wrists, the body would stay in position indefinitely, thus proving that the wrists are much more robust than the hands. And by such means does human knowledge creep forward.

The foot has to be three different things: shock absorber, platform, and pushing organ.

ostriches have eliminated this problem by fusing the bones of their feet and ankle, but then ostriches have had 250 million years to adjust to upright walking, roughly forty times as long as we have had.

No ape can be trained to walk like a human. They are compelled by their bone structure to waddle, and to do so in a most inefficient way.

To keep from overheating when we exert ourselves, we became relatively hairless and developed abundant sweat glands.

Walking and talking probably went hand in hand.

It is the nuchal ligament, and it has just one job: to hold the head steady when running.

But put us up against an antelope or wildebeest on a hot day and allow us to trot after it, and we can run it into the ground. We perspire to keep cool, but quadrupedal mammals lose heat by respiration—by panting. If they can’t stop to collect themselves, they overheat and become helpless.

As well as strengthening bones, exercise boosts your immune system, nurtures hormones, lessens the risk of getting diabetes and a number of cancers (including breast and colorectal), improves mood, and even staves off senility.

Clearly, any ambulation is likely to be beneficial, but the notion that there is a universal magic number of steps that will give us health and longevity is a myth.

“If you want to understand the human body, you have to understand that we evolved to be hunter-gatherers. That means being prepared to expend a lot of energy to acquire food, but not wasting energy when you don’t need to.”

“you can’t digest food while you are exercising because the body shunts blood away from the digestive system in order to meet the increased demand to supply oxygen to the muscles. So you have to rest sometimes just for metabolic purposes and to recover from the exertions of exercise.”

BMI is a person’s weight in kilograms divided by the square of their height in meters.

“You can’t undo sitting.”

Heat is lost at the surface, so the more surface area you have relative to volume, the harder you must work to stay warm.

the hypothalamus, which tells the body to cool itself by sweating or to warm itself by shivering and diverting blood flow away from the skin and into the more vulnerable organs.

Curiously, no one knows quite why this happens—whether fevers are an innate defense mechanism aimed at killing invading pathogens or simply a by-product of the body working hard to fight off infection.

The question is important because if fever is a defense mechanism, then any effort to suppress or eliminate it may be counterproductive. Allowing a fever to run its course (within limits, needless to say) could be the wisest thing.

An increase of only a degree or so in body temperature has been shown to slow the replication rate of viruses by a factor of two hundred—an astonishing increase in self-...

“If fever is such an ancient response to infection, one would think that the mechanism by which it benefits the host would be easy to determine. In fact, it has been difficult.”

The temperature we have is a reasonable compromise between utility and cost, as with most things, and actually even normal temperature is pretty good at keeping microbes in check.

Maintaining equilibrium within the body is called homeostasis.

Curious to understand why our stomachs gurgle when we are hungry, he persuaded a student named Arthur L. Washburn to train himself to overcome the gag reflex in order to push a rubber tube down his throat and into his stomach, where a balloon on its end could be inflated to measure the contractions when he was deprived of food.

The Wisdom of the Body, outlining the body’s extraordinary ability to regulate itself.

Put another way, the amount of electricity going on within your cells is a thousand times greater than the electricity within your house. You are, in a very small way, exceedingly energetic.

Every molecule of ATP is like a tiny battery in that it stores up energy and then releases it to power all the activities required by your cells—and indeed by all cells, in plants as well as animals.

Body size has a great deal to do with how we are affected by gravity.

A child half your height who falls and strikes her head will experience only one thirty-second the force of impact that a grown person would feel, which is part of the reason that children so often seem to be mercifully indestructible.

Dying is, to coin a phrase, the last thing your body wants to do.

Children do much better with extreme cold than with extreme heat. Because their sweat glands aren’t fully developed, they don’t sweat freely as adults do.

It is a sobering thought that 96 percent of our planet is off-limits to us.

Life at the Extremes

The increase in red cells makes the blood thicker and more sluggish and puts extra pressure on the heart when pumping, and that can apply even to those who have lived their whole lives at great heights.

The facility was known as Unit 731.

Shiro Ishii, the physician who had conceived and run Unit 731, was extensively debriefed and then allowed to return to civilian life.

The existence of Unit 731 was a well-guarded secret, by Japanese and American officials alike, and would have remained unknown to the wider world forever except that in 1984 a student from Keio University in Tokyo came across a box of incriminating documents in a secondhand bookshop and brought them to the attention of others.

THE IMMUNE SYSTEM is big and kind of messy and all over the place.

If you want to understand the immune system, you need to understand antibodies, lymphocytes, cytokines, chemokines, histamine, neutrophils, B cells, T cells, NK cells, macrophages, phagocytes, granulocytes, basophils, interferons, prostaglandins, pluripotent hematopoietic stem cells, and a great deal more—and I mean a great deal more.

Some of these overlap and some do multiple jobs. Interleukin-1, for instance, not only attacks pathogens but also plays a role in sleep, which may go some way to explaining why we are so often drowsy when unwell.

Moreover, the immune system doesn’t just deal with germs. It has to respond to toxins, drugs, cancers, foreign objects, and even your own state of mind.

If you are stressed or exhausted, you are much more likely to suffer an infection, for instance. Because protecting us from invasion is such a limitless challenge, the immune system sometimes makes mistakes and launches an attack on innocent cells.

“You could look at it and conclude that it’s crazy that the immune system attacks itself,” says Davis. “Alternatively, once you start to think about all that the immune system has to do, it’s surprising that it doesn’t happen all the time. Your immune system is constantly bombarded by things it has never seen before, things that may have only just come into existence—like new flu viruses, which are constantly mutating into new forms. So your immune system has to be able to identify and fight off a more or less infinite number of things.”

all parts of the immune system contribute to a single task: to identify anything that is in the body that shouldn’t be there and, if necessary, kill it.

David Bainbridge calls lymphocytes “just about the cleverest little cells in the whole body” because of their ability to recognize almost any kind of unwanted invader and mobilize a swift and targeted response.

For a very long time, the role of the thymus in the body was a complete mystery because it seemed to be just full of dead immune cells—“the place where cells went to die,”

What Miller established was that the thymus is a nursery for T cells.

T cells are a kind of elite corps in the immune system, and the dead cells found in the thymus were lymphocytes that had failed to pass muster because they were either not very good at identifying and attacking foreign invaders or because they were too eager to attack the body’s own healthy cells.

Killer T cells, as the name suggests, kill cells that have been invaded by pathogens. Helper T cells help other immune cells act, including helping B cells produce antibodies. Memory T cells remember the details of earlier invaders and are therefore able to coordinate a swift response if the same pathogen shows up again—what is known as adaptive immunity.

Microbes have developed various ways of fooling the immune system—by sending out confusing chemical signals, for instance, or by disguising themselves as benign or friendly bacteria.