The Body: A Guide for Occupants

by Bill Bryson

In addition, as well as killing invasive cells, the immune system must endeavor to kill our own cells when they misbehave, as when they turn cancerous.

Inflammation is essentially the heat of battle as the body defends itself from damage.

When they encounter an invader, they fire off attack chemicals called cytokines, which is what makes you feel feverish and ill when your body is battling infection.

The pus that seeps from a wound is simply dead white cells that have given their lives in defense of you.

“the immune system gets so ramped up that it brings out all its defenses and fires all its missiles in what is known as a cytokine storm. That’s what kills you. Cytokine storms show up again and again in many pandemic diseases, but also in things like extreme allergic reactions to bee stings.”

“For all the clinical good-will and perhaps even mortal urgency that accompanies their transplantation, skin homografts are treated as if they were a disease of which their destruction is the cure,”

It wasn’t until the development of the miracle drug cyclosporine from a soil sample fortuitously collected on a Norwegian holiday (as you will recall from chapter 7) that transplants could start to become routine.

To begin with, they affect the entire immune system, not just the transplanted part, so the patient is left permanently vulnerable to infections and to cancers, which the immune system would normally tackle. The drugs can also be toxic.

Equally bewildering is that autoimmune diseases are grossly sexist.

The largest and in many ways most mystifying and intractable category of immune disorders is allergies.

The richer the country, the more allergies its citizens get.

The bottom line in either case is that we don’t know why allergies exist at all.

Finding ways of using the body’s own immune defenses to fight diseases—what is known as immunotherapy—has the promise of transforming whole areas of medicine.

Cancers have learned to exploit this by sending out stop signals of their own, fooling the immune system into retiring prematurely.

Checkpoint therapy simply overrides the stop signals.

but essentially it involves genetically altering a cancer sufferer’s T cells, then returning them to the body in a form that allows them to attack and kill cancer cells.

QUIETLY AND RHYTHMICALLY, awake or asleep, generally without thought, every day you breathe in and out about 20,000 times,

Every time you breathe, you exhale some 25 sextillion (that’s 2.5 x 1022) molecules of oxygen—so many that with a day’s breathing you will in all likelihood inhale at least one molecule from the breaths of every person who has ever lived. And every person who lives from now until the sun burns out will from time to time breathe in a bit of you. At the atomic level, we are in a sense eternal.

“Sinuses are strange,”

“They are just cavernous spaces in your head. You would have room for a good deal more gray matter if you didn’t have to devote so much of your head to the sinuses.”

The space isn’t a complete void, but rather is riddled with a complex network of bones, which are thought to help with breathing effici...

Incidentally, the reason your nose runs in chilly weather is the same reason your bathroom windows run with water in chilly weather. In the case of your nose, warm air from your lungs meets cold air coming into the nostrils and condenses, resulting in a drip.

If an invading particle is big or especially irritating, you will almost certainly cough or sneeze it straight back out again (often in the process making it someone else’s problem). If it is too small to provoke such a vehement response, it will in all likelihood be trapped in the mucus that lines your nasal passages or caught by the bronchi, or tubules, in your lungs. These tiny airways are lined with millions and millions of hairlike cilia that act like paddles (but beating furiously at sixteen times a second), and they swat the invaders back into the throat, where they are diverted to the stomach and dissolved by hydrochloric acid.

An interesting theory is that weather and temperature may influence how the droplets in a sneeze coalesce, which could explain why flu and colds are more common in cold weather, but that still doesn’t explain why infectious droplets are more infectious to us when we pick them up by touch rather than when we breathe (or kiss) them in.

Altogether the lungs weigh about 2.4 pounds, and they take up more space in your chest than you probably realize.

Air pressure in the chest is less than atmospheric pressure, which helps to keep the lungs inflated. If air gets into the chest, because of a puncture wound, say, the differential vanishes and the lungs collapse to only about a third of their normal size.

Breathing is one of the few autonomic functions that you can control intentionally, though only up to a point.

Interestingly, the discomfort you feel when you hold your breath for too long is caused not by the depletion of oxygen but by a buildup of carbon dioxide. That’s why the first thing you do when you stop holding your breath is blow out. You would think that the most urgent need would be to get fresh air in rather than stale air out, but no.

Globally, asthma is more common among boys than girls before puberty, but more common in girls than boys after puberty.

There is no cure, though in 75 percent of young people asthma resolves itself by the time they reach early adulthood. No one knows how or why that happens either, or why it doesn’t happen for the unfortunate minority.

However, asthma remains the fourth leading cause of childhood death in Britain.

“I have spent thirty years studying asthma, and the main thing I have achieved is to show that almost none of the things people think cause asthma actually do. They can provoke attacks if you have asthma already, but they don’t cause it. We have very little idea what the primary causes are. We can do nothing to prevent it.”

“the dogma was that asthma was a neurological disease—the nervous system sending the wrong signals to the lungs. Then, in the 1950s and ’60s, the idea came along that it is an allergic reaction, and that has pretty much stuck. Even now textbooks say that the way people get asthma is by being exposed to allergens early in life. Basically everything in that theory is wrong. It’s clear now that it is considerably more complicated than that. We now know that half the cases in the world involve allergies, but half are due to something else altogether—to nonallergic mechanisms. We don’t know what those are.”

“the dogma is that both allergic and nonallergic asthmas involve inflammation in the lungs, but with some asthmatics if you put their feet in a bucket of ice water, they begin to wheeze immediately. Now, that can’t be due to inflammation, because it happens too fast. It has to be neurological. So now we are coming full circle for at least part of the answer.”

“If you test the lung function of asthmatics, most of the time for most of them it will be completely normal. It’s only when they have an attack that problems with lung function become apparent and detectable. That’s very unusual for a disease. Even when there are no symptoms present, the disease will nearly always be evident in blood or sputum tests. In asthma, in some cases, the disease just vanishes.”

In an asthma attack, the airways narrow, and the sufferer struggles to get air in or out, especially out.

“All we can really say about asthma is that it is primarily a Western disease,”

Pearce made a curious discovery—that people who had had a cat early in life seemed to derive lifelong protection from getting asthma.

A person who smokes cigarettes regularly (about a pack a day) is fifty times more likely than a nonsmoker to get cancer.

Although two of the world’s most prestigious medical journals had now demonstrated a clear association between smoking and lung cancer, the findings had almost no effect.

As late as 1973, Nature ran an editorial backing women’s smoking during pregnancy on the grounds that it calmed their stress.

A hiccup is a sudden spasmodic contraction of the diaphragm, which essentially startles the larynx into closing abruptly, making the famous hic sound. No one knows why they happen.

If you do get hiccups and they don’t go away spontaneously after a few minutes, medical science is at a more or less complete loss to help you.

But what exactly are these little numerical oddments that are so keen to make us round and wobbly?

The calorie is a strange and complicated measure of food energy. Formally, it’s a kilocalorie, and it is defined as the amount of energy required to heat one kilogram of water by one degree centigrade, but it seems safe to say that no one ever thinks of it in those terms when deciding what foods to eat.

The father of caloric measurement—indeed of modern food science—was the American academic Wilbur Olin Atwater.

Atwater chose the latter and, undeterred, worked out the calories and nutritional values of practically all known foods—some four thousand in all.

By whatever means you measure it, we are pretty good at extracting energy from food, not because we have an especially dynamic metabolism but because of a trick we learned a very long time ago: cooking.

It is widely believed now that cooked food gave us the energy to grow big brains and the leisure to put them to use.

“You can’t possibly have a large brain unless you’ve got the energy to fuel it,”