The Body: A Guide for Occupants

by Bill Bryson

The heart must pump with enough force not merely to send blood to your outermost extremities but to help bring it all the way back again. If you are standing, your heart is roughly four feet above your feet, so there’s a lot of gravity to overcome on the return trip. Imagine squeezing a pump the size of a grapefruit with enough force to move a fluid four feet up a tube.

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 output of the two must be in balance, every single time, for it all to work correctly. Of all the blood pumped out of your heart, the brain takes 15 percent,

journey of blood around your body takes about fifty seconds to complete. Curiously, the blood passing through the chambers of the heart does nothing for the heart itself. 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 difference between these two is your blood pressure. 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 blood vessels experience with each heartbeat. The first, higher number is the systolic pressure; the second, the diastolic. The numbers specifically

Keeping every part of the body supplied with sufficient quantities of blood at all times is a tricky business. 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. To contract, however, they need to be in motion. That’s why it’s important to get up and move around regularly. On the whole, the body manages these challenges pretty well. “For healthy people there is a less than 20 percent difference

What exactly constitutes high blood pressure? For a long time, a reading of 140/90 was generally considered the baseline for hypertension, but in 2017 the American Heart Association surprised nearly everyone by abruptly pushing the number downward to 130/80. That small reduction tripled the number of men and doubled the number of women aged forty-five or under who were deemed to have high blood pressure and lifted practically all people over sixty-five into the danger zone. Almost half of all American adults—103 million

though usually confused by most of us, are in fact two different things. A heart attack occurs when oxygenated blood can’t get to heart muscle because of a blockage in a coronary artery. Heart attacks are often sudden—that’s why they are called attacks—whereas other forms of heart failure are often (though not always) more gradual. When heart muscle downstream of a blockage is deprived of oxygen, it begins to die, usually within

Cardiac arrest is when the heart stops pumping altogether, usually because of a failure in electrical signaling. When the heart stops pumping, the brain is deprived of oxygen and unconsciousness swiftly follows, with death not far behind unless treatment is quickly applied. A heart attack will often lead to cardiac arrest, but you can suffer cardiac arrest without having a heart attack. The distinction between the two is medically important because they require different treatments, though the distinction may be a touch academic to the sufferer. All forms of heart failure can be cruelly sneaky.

For about a quarter of victims, the first (and, more unfortunately, last) time they know they have a heart problem is when they suffer a fatal heart attack. No less appallingly, more than half of all first heart attacks (fatal or otherwise) occur in people who are fit and healthy

They don’t smoke or drink to excess, are not seriously overweight, and do not have chronically high blood pressure or even bad cholesterol readings, but they get a heart attack anyway. Living a virtuous life doesn’t guarantee that you will escape heart problems; it just improves your chances. 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 be...

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.” For a lucky few victims (insofar as good fortune can be attached to a fatal event), death comes so swiftly that they appear to feel no pain. My own father went to bed one night in 1986 and never woke up. As far as could be told, he died without pain or distress or indeed awareness. For reasons unknown, the Hmong people of Southeast Asia are particularly susceptible to a condition known as sudden unexplained nocturnal death syndrome. In it, victims’ hearts simply stop beating while they are asleep. Autopsies nearly always show the hearts to look normal and healthy.

suddenly on playing fields. It arises from an unnatural (and nearly always undiagnosed) thickening of one of the ventricles and causes eleven thousand sudden unexpected deaths a year among people under forty-five in the United States. The heart has more named conditions than just about any other organ, and they are all bad news. If you can go through life without experiencing Prinzmetal angina, Kawasaki disease, Ebstein’s anomaly, Eisenmenger syndrome, Takotsubo

The triggering event for public awareness seems to have been the death of Franklin Delano Roosevelt. In early 1945, his blood pressure soared to 300/190, and it was clear that this was not a sign of vigor but quite the opposite. When he died soon afterward, aged just sixty-three, the world seemed suddenly to realize that heart disease had become a serious and widespread problem and that it was time to try to do something about it. The result was the celebrated Framingham Heart Study, conducted in the town of Framingham, Massachusetts, just west of Boston. Starting in the autumn of 1948, the Framingham study recruited five thousand local adults

Larsson, a forty-three-year-old patient (and himself an engineer) who was very near death from a heart arrhythmia as a result of a viral infection. The device failed after just a few hours. The backup was inserted and it lasted for three years, though it kept breaking down and the batteries had to be recharged every few hours. As technology improved, Larsson was routinely fitted with new pacemakers and lived another forty-three years. When he died in 2002 at the age of eighty-six, he was on his twenty-sixth pacemaker and had outlived both his surgeon Senning and his fellow engineer Elmqvist. The first pacemaker was about the size of a pack of cigarettes. Today’s are no bigger than one American quarter and can last up to ten years.

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. Favaloro’s was a story at once inspiring and tragic. He grew up poor in Argentina and became the first member of his family to attain a higher education. Upon qualifying as a doctor, he spent twelve years working among the poor but came to the United States in the 1960s to improve his skills. At the Cleveland Clinic, he was little more than a trainee at first but quickly proved himself adept at heart surgery and in 1967 invented

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

Remarkably, even with all the improvements in care, you are 70 percent more likely to die from heart disease today than you were in 1900. That’s partly because other things used to kill people first, and partly because a hundred years ago people didn’t spend five or six hours an evening in front of a television with a big spoon and a tub

Today the problem is as likely to be overtreatment as under, according to some authorities. Balloon angioplasties as a treatment for angina (or chest pains) are a case in point, it seems. With an angioplasty, a balloon is inflated inside a constricted coronary blood vessel to widen it, and a stent, or piece of tubular scaffolding, is left behind to keep the vessel permanently open.*2 The operation is unquestionably a lifesaver in emergencies, but it has also proven highly popular as an elective procedure. By 2000, a million precautionary angioplasties were being

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). Despite this, angioplasties remain extremely popular. In 2013,

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

discard about a hundred billion red blood cells every day. They are a big component of what makes your stools brown. (Bilirubin, a by-product of the same process, is responsible for the golden glow of urine as well as the yellow blush of fading bruises.) —

You have seven hundred times as many red blood cells as white ones, which constitute less than 1 percent of the total.*3 Platelets (or thrombocytes), the final part of the blood quartet, also account

Clotting doesn’t work in the principal arteries, because the flow of blood is too fierce; any clot would be swept away, which is why major bleeds must be stopped with the pressure of a tourniquet. In severe bleeding, the body does all it can to keep blood flowing to the vital organs and diverts it away from secondary outposts like muscles and surface tissues. That’s why patients who are bleeding heavily turn a cadaverous white and are cold to the touch. Platelets live

Harvey outlined all the details of how the heart and circulatory system work, in more or less the terms we understand today. When I was a schoolboy, this was always presented as one of those eureka moments that changed the world. In fact, in Harvey’s day the theory was almost universally ridiculed and rejected. Nearly all Harvey’s peers thought him “crack-brained,” in the words of the diarist John Aubrey. Harvey was abandoned by most of his clients and died a bitter man. Harvey didn’t understand respiration, so couldn’t explain what purpose blood served or why it circulated—two pretty glaring deficiencies, as his critics were quick to point out. Galenists additionally believed that the body contains two

now know that blood traveling from the lungs is full of oxygen and therefore shiny crimson, while blood returning to the lungs is depleted of oxygen and thus rather duller. Harvey couldn’t explain how blood circulating in a closed system could be of two colors, which became yet another reason to scorn his theories. The secret

way blood typing works is this: All blood cells are the same inside, but the outsides are covered with different kinds of antigens—that is, proteins that project outward from the cell surface—and that is what accounts for blood types. There are some four hundred kinds of antigens altogether, but only a few have an important effect on transfusion, which is why we have all heard of types A, B, AB, and O, but not, say, Kell,

People with O blood, for instance, are more resistant to malaria but less resistant to cholera. By developing a variety of blood types and spreading them around among populations, we benefit the species, if not always the individuals within it. Blood typing had a second, unanticipated benefit: establishing

turned out that in some cases it can be better to let patients be anemic than to give them someone else’s blood, especially if that blood had been in storage for a while—and that is nearly always the case. When a blood bank receives a call for blood, it normally dispatches the oldest blood first, to use up aging stock before it expires, which means that almost everybody receives old blood. Worse still, it was discovered that even fresh transfused blood actually impedes the performance of existing blood in the recipient’s body. This is where nitric oxide comes in. Most of us think of blood as being more or less

an experiment at Stanford Hospital in California, clinicians were encouraged to reduce orders for red blood cell transfusions except when absolutely required. In five years, transfusions at the hospital fell by a quarter. The result was not only a $1.6 million saving in costs but fewer deaths, quicker average discharges, and a reduction in posttreatment complications. Now, however, Doctor and his colleagues in St. Louis think they have nearly cracked the problem. “We have nanotechnology at our disposal now, which wasn’t available before,”

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. *4 Rh factor

Then, in late 1920, in one of the happiest but most improbable episodes in the history of scientific progress, a struggling young general practitioner in London, Ontario, read an article about the pancreas in a medical journal and got an idea for how he might effect a cure. His name was Frederick Banting, and he knew so little about diabetes that he misspelled it as “diabetus” in his notes. He had no experience of medical research, but

given to diabetics, the effect was nothing short of miraculous. Listless, skeletal patients who could barely be called alive were swiftly restored to full vibrancy. It was, to borrow from Michael Bliss, author of the definitive The Discovery of Insulin, the closest thing to resurrection modern medicine had ever produced. Another researcher in the lab, J.

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. They come in different sizes, have different chemistries, go to different places, have different effects when they get there. Some are proteins, some are steroids, some are from a group called amines. They are linked by their purpose, not their chemistry. Our understanding of them is far from complete, and much of what we do know is surprisingly recent. John Wass, professor

Wass is a tireless campaigner for a better appreciation of hormones and what they do for us. “They were the last major system in the body to be discovered,” he says. “And we are still discovering more all the time. I know I am biased, but it is really a terribly exciting field.” As late as 1958, only about twenty hormones were known. No one seems to know quite how many there are now. “Oh, I think it must be at least eighty,” says Wass, “but perhaps as many as a hundred now. We really do keep discovering more all the time.” Until very recently, it was thought that hormones are produced exclusively in the body’s endocrine glands (hence the name endocrinology for this branch of medicine). An endocrine gland is one that secretes its products directly into the bloodstream, as opposed to exocrine glands, which secrete onto a surface (like sweat glands onto skin or salivary glands into the mouth). The principal endocrine glands—the thyroid, parathyroid, pituitary, pineal, hypothalamus, thymus, testes (in men), ovaries (in women), pancreas—are scattered all around the body but work together closely. They are mostly tiny and altogether weigh no more than a few ounces but have an importance to your happiness and well-being that is entirely disproportionate to their modest dimensions.

Robert Wadlow of Alton, Illinois, the tallest human who ever lived to that point, had a pituitary condition that caused him to grow ceaselessly because of continuous overproduction of growth hormone. A shy and cheerful soul, he was taller than his (normal-sized) father by the age of eight, was 6 feet 11 inches tall at the age of twelve, and over 8 feet tall when he graduated from high school in 1936—all because of a little chemical overexertion by this baked bean in the middle of his skull. He never stopped growing and was just a fraction under 9 feet tall at his greatest eminence. Though not fat, he weighed about five hundred pounds. His shoes were a size 40. By his early twenties, he could walk only with great difficulty. To support himself,

which caused chafing, and that led to a serious infection that grew septic and killed him as he slept on July 15, 1940. He was just twenty-two. His height at death was 8 feet 11.1 inches. He was much loved and is still celebrated in his hometown. It is clearly ironic that such a large body resulted from a malfunction in a minuscule gland.

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

Arguably the real father of endocrinology lived a generation before Brown-Séquard. Thomas Addison (1793–1860) was one of a trio of outstanding doctors, known as the Three Greats, at Guy’s Hospital in London in the 1830s. The others were Richard Bright, discoverer of Bright’s disease (now called nephritis), and Thomas Hodgkin, who specialized in disorders of the lymphatic system and whose

At least five serious medical conditions were named for him, of which the most famous was (and remains) Addison’s disease, a degenerative disorder of the adrenal glands that Addison described in 1855, making it the first hormonal disorder to be identified. Despite his fame, Addison was subject to spells of depression, and in 1860, five years after identifying Addison’s, he retired to Brighton and killed himself. Addison’s disease is a rare but still-serious illness. It affects about one person in ten thousand. History’s most famous sufferer was John F. Kennedy, who was diagnosed with it in 1947, though he and his family always emphatically and untruthfully denied

Kennedy not only had Addison’s but was lucky to survive it. In those days, before the introduction of glucocorticoids, a type of steroid, 80 percent of sufferers died within a year of diagnosis. John Wass, at the time we met, was particularly preoccupied with Addison’s disease. “It can be a very sad disease because the symptoms—principally loss of appetite and weight loss—are easily misdiagnosed,” he told me. “I recently dealt with the case of a really lovely young woman, just twenty-three years old and with a very promising future in front of her, who died of Addison’s because her doctor thought she was suffering from anorexia and sent her to a psychiatrist. Addison’s in fact arises from an imbalance of cortisol levels—cortisol being a stress hormone that regulates blood pressure. The tragedy of it is that if you correct the cortisol problem, the patient can return

Leptin drew massive and immediate interest not just because of the surprise of where it was produced but even more because of what it does: it helps to regulate appetite. If we could control leptin, then presumably we could help people to control their weight. In studies with rats, scientists discovered that by manipulating leptin levels, they could make rats obese or lean, as they wished. This had the makings of a wonder drug. Clinical trials with humans were quickly undertaken, amid considerable anticipation.

bodies evolved to deal with the challenge of dietary paucity, not overabundance. So leptin isn’t programmed to tell you to stop eating. Nothing chemical in your body is. That’s a big part of why you tend to just keep on consuming. We are

your hormones think you are starving, those processes will not be allowed to begin. That’s why young people who are anorexic often have a very delayed start to puberty. “It’s also almost certainly why puberty starts years earlier now than it did in historic times,” says Wass. “In Henry VIII’s reign, puberty started at sixteen or seventeen. Now it is more commonly eleven. That’s almost certainly because of improved nutrition.” Complicating matters further is that bodily processes are

Many factors determine life span, of course, but it is a fact that men who have been castrated live about as long as women do. In what way exactly testosterone might shorten male lives is not known. Testosterone levels in men fall by about 1 percent a year beginning in their forties, prompting many to take supplements in the hope of boosting their sex drive and energy levels. The evidence that it improves sexual performance or general virility is thin at best; there is much greater evidence that it can lead to an increased risk of heart attack or stroke.

NOT ALL GLANDS are tiny, of course. (For the record, a gland is any organ in the body that secretes chemicals.) The liver is a gland and it is, compared with the rest of our glands, gigantic. When fully

and fills much of the central abdomen just below the diaphragm. It is disproportionately large in infants, which is why their bellies are so delightfully rounded.

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. Perhaps the most wondrous feature of the liver is its capacity to regenerate. You can remove two-thirds of a liver and it will grow back to its original size in just a few weeks. “It’s not pretty,” the Dutch geneticist Professor Hans Clevers told me. “It looks a bit battered and rough compared with the original liver, but it functions well enough. The process is something of a mystery. We don’t know how a liver knows to grow back to just the right size and then stop growing, but it is lucky for some of us that it does.” The liver’s resilience is not infinite, however. It is subject to more than a hundred disorders, and many of these are grave. Most ...

Nonalcoholic fatty liver disease (NAFLD) is an illness most of us have never heard of, but it is more common than cirrhosis, and far more baffling. It is, for instance, strongly associated with being overweight or obese, and yet a significant proportion of sufferers are fit and lean. No one can explain why. Altogether about a third of us are thought to have early stages of NAFLD, but luckily for most of us it never progresses

Perhaps the most unnerving aspect is that victims usually suffer no symptoms at all until most of the damage has been done. Even

estimated 10.7 percent of children and adolescents in the United States and 7.6 percent globally are estimated to have fatty livers. Another risk that many people aren’t fully aware of is hepatitis C. According to the Centers