The Body: A Guide for Occupants

by Bill Bryson

The victims have included a great many distinguished figures—Aristotle, Virgil, Charles Darwin, Lewis Carroll, Winston Churchill (when young), Henry James, John Updike, Marilyn Monroe, and King George VI of Great Britain, who was sympathetically portrayed by Colin Firth in the 2010 movie The King’s Speech.

Of all the blood pumped out of your heart, the brain takes 15 percent, but actually the greatest amount, 20 percent, goes to the kidneys.

The journey of blood around your body takes about fifty seconds to complete.

The oxygen that nourishes it arrives via the coronary arteries, in exactly the way oxygen reaches other organs.

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 two numbers in a blood pressure reading—let’s say 120/80, or “120 over 80” when spoken—simply measure the highest and lowest pressures your bloo...

No two heart attacks are quite the same, it seems. Women and men have heart attacks in different ways. A woman is more likely to experience abdominal pain and nausea than a man, which makes it more likely that the problem will be misdiagnosed. Partly for this reason, women who have heart attacks before their mid-fifties are twice as likely to die as a man. Women have more heart attacks than is generally supposed. Twenty-eight thousand women suffer fatal heart attacks in the U.K. each year; about twice as many die of heart disease as die of breast cancer. Some people who are about to experience catastrophic heart failure suffer a sudden, terrifying premonition of impending death. The condition is commonly enough observed that it has a medical name: angor animi, or “anguish of the soul.”

The coronary bypass, which involved taking a length of healthy vein from a person’s leg and transplanting it to direct blood flow around a diseased coronary artery, was devised in 1967 by René Favaloro at the Cleveland Clinic in Ohio.

Following Barnard, other nations moved to let brain death be used as an alternative measure of irreversible lifelessness, and soon heart transplants were being attempted all over, though nearly always with discouraging results. The main issue was an absence of a wholly reliable immunosuppressive drug to deal with rejection. A drug called azathioprine worked sometimes but couldn’t be relied on. Then, in 1969, an employee of the Swiss pharmaceutical company Sandoz named H. P. Frey, while on holiday in Norway, collected soil samples to take back to the Sandoz labs. The company had asked employees to do so when traveling in the hope that they would find potential new antibiotics. Frey’s sample contained a fungus, Tolypocladium inflatum, which had no useful antibiotic properties but proved excellent at suppressing immune responses—just the thing needed to make organ transplants possible. Sandoz converted Herr Frey’s little bag of dirt, and a similar sample subsequently found in Wisconsin, into a best-selling medicine called cyclosporine. Thanks to it and some associated technical improvements, by the early 1980s heart transplant surgeons were managing success rates of 80 percent, an extraordinary achievement in a decade and a half. Today some four to five thousand heart transplants are performed globally each year, with an average survival time of fifteen years. The longest-surviving transplant patient so far is Fiona Coote of Australia, who has had two heart transplants since ...

When clinical trials were finally undertaken, the results were sobering. According to The New England Journal of Medicine, for every one thousand nonemergency angioplasties in America, two patients died on the operating table, twenty-eight suffered heart attacks brought on by the procedure, between sixty and ninety experienced a “transient” improvement in their health, and the rest—about eight hundred people—experienced neither benefit nor harm (unless of course you count the cost, the loss of time, and the anxiety of surgery as harm, in which case there was plenty).

Spin a test tube of blood in a centrifuge and it will separate into four layers: red cells, white cells, platelets, and plasma. Plasma is the most abundant, constituting a little over half of blood’s volume. It is more than 90 percent water with some salts, fats, and other chemicals suspended in it. That isn’t to say plasma is unimportant, however. It is anything but. Antibodies, clotting factors, and other constituent parts can be separated out and used in concentrated form to treat autoimmune diseases or hemophilia—and that is a huge business. In the United States, plasma sales make up 1.6 percent of all goods exported, more than America earns from the sale of airplanes.

Red blood cells (formally called erythrocytes) are the next most plentiful component, constituting about 44 percent of the total volume of the blood. Red blood cells are exquisitely designed to do one job: deliver oxygen. They are very small but superabundant. A teaspoon of human blood contains about twenty-five billion red blood cells, and each one of those twenty-five billion contains 250,000 molecules of hemoglobin, the protein to which oxygen willingly clings. Red blood cells are biconcave in shape—that is, disk shaped but pinched in the middle on both sides—which gives them the largest possible surface area. To make themselves maximally efficient, they have jettisoned virtually all the components of a conventional cell—DNA, RNA, mitochondria, Golgi apparatus, enzymes of every description. A full red blood cell is almost entirely hemoglobin. It is essentially a shipping container. 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.

Hemoglobin has one strange and dangerous quirk: it vastly prefers carbon monoxide to oxygen. If carbon monoxide is present, hemoglobin will pack it in, like passengers on a rush-hour train, and leave the oxygen on the platform. That’s why it kills people. (About 430 of them a year in the United States unintentionally, and a similar number by suicide.)

Each red corpuscle survives for about four months, which is pretty good going considering what a jostling and busy existence it leads. Each will be shot around your body about 150,000 times, logging a hundred miles or so of travel before it is too battered to go on. Then these corpuscles are collected by scavenger cells and sent to the spleen for disposal. You discard about a hundred billion red blood cells every day. They are a big component of what makes your stools brown. (Bilirubin...

They are defined as any substance that is produced in one part of the body and causes an action somewhere else, but beyond that they are not easy to characterize.

It is clearly ironic that such a large body resulted from a malfunction in a minuscule gland. The pituitary is often called the master gland because it controls so much. It produces (or regulates the production of) growth hormone, cortisol, estrogen and testosterone, oxytocin, adrenaline, and much else. When you exercise vigorously, the pituitary squirts endorphins into your bloodstream. Endorphins are the same chemicals released when you eat or have sex. They are closely related to opiates. That’s why it is called the runner’s high. There is barely a corner of your life that the pituitary doesn’t touch, yet its functions weren’t even broadly understood until well into the twentieth century.

Oxytocin, to take one example, is well known for its role in generating feelings of attachment and affection—it is sometimes called “the hug hormone”—but it also plays an important part in facial recognition, in directing contractions of the uterus in childbirth, in interpreting the moods of people around us, and in initiating the production of milk by nursing mothers.

It is also the most multifariously busy organ in the body, with functions so vital that if it shuts down, you will be dead within hours. Among its many jobs, it manufactures hormones, proteins, and the digestive juice known as bile. It filters toxins, disposes of obsolescent red blood cells, stores and absorbs vitamins, converts fats and proteins to carbohydrates, and manages glucose—a process which is so vital for the body that its dilution for even a few minutes can cause organ failure and even brain damage. (Specifically the liver converts glucose into glycogen—a more compact chemical. It is a little bit like shrink-wrapping food so you can pack more of it into your freezer. When energy is needed, the liver converts the glycogen back into glucose and releases it into the bloodstream.) 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.

They are startlingly small for the amount of work they do, weighing just five ounces each. They are not in the small of the back, as everyone thinks, but higher up, about at the bottom of the rib cage. The right kidney is always lower because it is pressed down upon by the asymmetrical liver. Filtering wastes is their principal function, but they also regulate blood chemistry, help maintain blood pressure, metabolize vitamin D, and maintain the vital balance between salt and water levels within the body. Eat too much salt and your kidneys filter out the excess from your blood and send it to the bladder so that you can pee it all away. Eat too little and the kidneys take it back from the urine before it leaves your body. The problem is that if you ask the kidneys to do too much filtering

Apart from anything else, it could help to explain the long-standing mystery of how regular exercise helps to stave off Alzheimer’s disease: exercise builds stronger bones and stronger bones produce more osteocalcin.

Tendons and ligaments are connective tissues. Tendons connect muscles to bone; ligaments connect bone to bone.

Tendons are stretchy; ligaments, less so.

Tendons are essentially extension...

For the longest time, the crucial importance to health of just moving around was hardly appreciated. But in the late 1940s a doctor at Britain’s Medical Research Council, Jeremy Morris, became convinced that the increasing occurrence of heart attacks and coronary disease was related to levels of activity, and not just to age or chronic stress, as was almost universally thought at the time. Because Britain was still recovering from the war, research funding was tight, so Morris had to think of a low-cost way to conduct an effective large-scale study. While traveling to work one day, it occurred to him that every double-decker bus in London was a perfect laboratory for his purposes because each had a driver who spent his entire working life sitting and a conductor who was on his feet constantly. In addition to moving about laterally, conductors climbed an average of six hundred steps per shift. Morris could hardly have invented two more ideal groups to compare. He followed thirty-five thousand drivers and conductors for two years and found that after he adjusted for all other variables, the drivers—no matter how healthy—were twice as likely to have a heart attack as the conductors. It was the first time that anyone had demonstrated a direct and measurable link between exercise and health.

As Daniel Lieberman explains, “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.” So exercise is important, but rest is vital, too. “For one thing,” Lieberman says, “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.”

One study in America found that people overestimate the number of calories they burned in a workout by a factor of four.

They also then consumed, on average, about twice as many calories as they had just burned off.

Despite the vast differences in heart rates, nearly all animals have about 800 million heartbeats in them if they live an average life. The exception is humans. We pass 800 million heartbeats after twenty-five years, and just keep on going for another fifty years and 1.6 billion heartbeats or so.

Alkemade’s survival adventures did not quite end there. After the war, he took a job in a chemical plant in Loughborough, in the English Midlands. While he was working with chlorine gas, his gas mask came loose, and he was instantly exposed to dangerously high levels of the gas. He lay unconscious for fifteen minutes before co-workers noticed his unconscious form and dragged him to safety. Miraculously, he survived. Some time after that, he was adjusting a pipe when it ruptured and sprayed him from head to foot with sulfuric acid. He suffered extensive burns but again survived. Shortly after he returned to work from that setback, a nine-foot-long metal pole fell on him from a height and very nearly killed him, but once again he recovered.

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. That is in large part why so many of them die so swiftly when left in cars in warm weather.

At sea level, about 40 percent of your blood volume is occupied by red blood cells, but that can increase by about half as much again with acclimatization to higher altitudes, though there is a price to be paid. 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.

In a typical experiment, Chinese prisoners were tied to stakes at staggered distances from a shrapnel bomb. The bomb was detonated and scientists then walked among them, carefully noting the nature and extent of the prisoners’ injuries and how long it took them to die. Other prisoners were shot with flamethrowers for similar purposes, or starved, frozen, or poisoned. Some, for unfathomable reasons, were dissected while still conscious. Most of the victims were captured Chinese soldiers, but Unit 731 also experimented on selected Allied prisoners of war to make sure that toxins and nerve agents had the same effects on Westerners as on Asians. When pregnant women or young children were needed for experiments, they were randomly snatched from the streets of Harbin. Nobody knows how many people died in Unit 731, but one estimate has put the number as high as 250,000.

Inflammation is essentially the heat of battle as the body defends itself from damage. Blood vessels in the vicinity of an injury dilate, allowing more blood to flow to the site, bringing with it white blood cells to fight off invaders. That causes the site to swell, increasing the pressure on surrounding nerves, resulting in tenderness.

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. It’s not the infection that makes you feel dreadful, but your body defending itself. The pus that seeps from a wound is simply dead white cells that have given their lives in defense of you.

“Sometimes,” Michael Kinch, from Washington University in St. Louis, explained to me, “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.”

Equally bewildering is that autoimmune diseases are grossly sexist. Women are twice as likely as men to get multiple sclerosis, ten times more likely to get lupus, fifty times more likely to suffer a thyroid condition known as Hashimoto’s thyroiditis. Altogether, 80 percent of all autoimmune diseases occur in women. Hormones are the presumed culprit, but how exactly female hormones trip up the immune system when male hormones don’t is not at all clear.

Allergy rates vary across the world from about 10 to 40 percent, with the rates closely following economic performance. The richer the country, the more allergies its citizens get. No one knows why being rich should be so bad for you.

may be that people of rich, urbanized nations are more exposed to pollutants—there is evidence that nitrogen oxides from diesel fuels correlate with higher incidences of allergies—or it may be that increased use of antibiotics in the rich nations has directly or indirectly affected our immune responses.

Most allergies merely cause discomfort, but some can be life threatening. About seven hundred people a year die in America from anaphylaxis, the formal name for an extreme allergic reaction causing restriction of airways. These reactions are brought on most often by penicillin, foods, insect stings, and latex,

In the case of your nose, warm air from your lungs meets cold air coming into the nostrils and condenses, resulting in a drip.

formal name for the act of sneezing, by the way, is sternutation, though some authorities in their lighter moments refer to a sneeze as an autosomal dominant compelling helio-ophthalmic

ophthalmic outburst, which makes the acronym ACHOO (sort

Globally, asthma is more common among boys than girls before puberty, but more common in girls than boys after puberty. It is more common in blacks than whites (generally but not everywhere) and in city people than rural people. In children, it is closely associated with both being obese and being underweight; obese children get it more often, but underweight children get it worse. The highest rate in the world is in the U.K., where 30 percent of children have shown asthma symptoms. The lowest rates are in China, Greece, Georgia, Romania, and Russia, with just 3 percent. All the English-speaking nations of the world have high rates, as do those of Latin America.

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,

Biotin, for instance, was for a time called vitamin H, but then became B7. Today it is mostly just called biotin.

PROTEINS ARE COMPLICATED molecules. About a fifth of our body weight is made up of them.

In simplest terms, a protein is a chain of amino acids.

Although all proteins are made from amino acids, there is no accepted definition as to how many amino acids you need in a chain to qualify as a protein.

All that can be said is that a small but unspecified number of amino acids strung together is a peptide. Ten or twelve strung together is a polypeptide. When a polypeptide begins to get bigger than that, it becomes, at some ineffable point, a protein.

CARBOHYDRATES ARE COMPOUNDS of carbon, hydrogen, and oxygen, which are bound together to form a variety of sugars—glucose, galactose, fructose, maltose, sucrose, deoxyribose (the stuff found in DNA), and so on. Some of these are chemically complex and known as polysaccharides, some are simple and known as monosaccharides, and some are in between and known as disaccharides.