The Body: A Guide for Occupants

by Bill Bryson

There is some evidence that a nursing mother absorbs a little of her suckling baby’s saliva through her breast ducts and that this is analyzed by her immune system, which adjusts the amount and types of antibodies she supplies to the baby, according to its needs.

Barker hypothesis or, a little less snappily, the theory of fetal origins of adult disease. Barker, an epidemiologist, posited that what happens in the womb can determine health and well-being for the rest of one’s life. “For every organ, there is a critical period, often very brief, when it goes through development,” he said not long before his death in 2013. “It happens for different organs at different times. After birth only the liver and the brain and the immune system remain plastic. Everything else is done.” Most authorities now extend that period of crucial vulnerability from the moment of your conception to your second birthday—what has become known as the first thousand days.

Exactly how pain works is, as you will gather, still largely a mystery. There is no pain center in the brain, no one place where pain signals congregate. A thought must travel through the hippocampus to become a memory, but a pain can surface almost anywhere.

Nociceptors respond to three kinds of painful stimuli: thermal, chemical, and mechanical, or at least so it is universally assumed.

all types of pain are conveyed on to the spinal cord and brain by two different types of fibers—fast-conducting A delta fibers (they’re coated in myelin, so slicker, as it were) and slower-acting C fibers. The swift A delta fibers give you the sharp ouch of a hammer blow; the slower C fibers give you the throbbing pain that follows. Nociceptors only respond to disagreeable (or potentially disagreeable) sensations. Normal touch signals—the feel of your feet against the ground, your hand on a doorknob, your cheek on a satin pillow—are conveyed by different receptors on a separate set of A-beta nerves.

most authorities divide headaches into two broader categories: primary headaches, such as migraine and tension headaches, which have no direct, identifiable cause, and secondary headaches, which arise from some other precipitating event, like an infection or tumor.

Being depressed or worried will almost always increase perceived levels of pain. But equally pain is decreased by pleasant aromas, soothing images, pleasurable music, good food, and sex. Just having a sympathetic and loving partner cuts the reported pain of angina by half, according to one study.

No less alarmingly, drug-resistant strains of TB now account for 10 percent of new cases.

Symptoms usually first appear when the victim is in his or her thirties or forties, and progress ineluctably to senility and premature death. It is all because of one mutation in the HTT gene, which produces a protein called huntingtin, one of the largest and most complex proteins in the human body, and we have no idea what huntingtin is for.

You are probably aware that all flus have names like H5N1 or H3N2. That is because every flu virus has two types of proteins on its surface—hemagglutinin and neuraminidase—and these account for the H and N in their names. H5N1 means that the virus combines the fifth known iteration of hemagglutinin with the first known iteration of neuraminidase, and for some reason that is a particularly nasty combination.

In 2000, a landmark paper in the journal Cell listed six attributes in particular that all cancer cells have, namely: They divide without limit. They grow without direction or influence from outside agents like hormones. They engage in angiogenesis, which is to say they trick the body into giving them a blood supply. They disregard any signals to stop growing. They fail to succumb to apoptosis, or programmed cell death. They metastasize, or spread to other parts of the body.

Eighty percent of cancers, known as carcinomas, arise in epithelial cells—that is, the cells that make up the skin and the linings of organs. Breast cancers, for instance, don’t just grow randomly within the breast, but normally begin in the milk ducts. Epithelial cells are assumed to be particularly susceptible to cancers because they divide rapidly and often. Only about 1 percent of cancers are found in connective tissue; these are known as sarcomas.

The rise of penicillin and other antibiotics like Albert Schatz’s streptomycin had an obvious and significant impact on infectious diseases,

If there is one thing that should alarm and concern us today, it is how unequally the benefits of the last century have been shared.

If you are middle-aged, exceptionally well-off, and from almost any high-income nation, the chances are excellent that you will live into your late eighties. Someone who is otherwise identical to you but poor—exercises as devotedly, sleeps as many hours, eats a similarly healthy diet, but just has less money in the bank—can expect to die between ten and fifteen years sooner.

Among rich countries, America is at or near the bottom for virtually every measure of medical well-being—for chronic disease, depression, drug abuse, homicide, teenage pregnancies, HIV prevalence. Even sufferers of cystic fibrosis live ten years longer on average in Canada than in the United States.

The unfortunate bottom line is that breast cancer screening doesn’t save a lot of lives. For every thousand women screened, four will die of breast cancer anyway (either because the cancer was missed or because it was too aggressive to be treated successfully). For every thousand women who are not screened, five will die of breast cancer. So screening saves one life in every thousand.

A meta-analysis of six randomized control trials involving 382,000 men found that for every 1,000 men screened for prostate cancer, about one life was saved—great news for that individual, but not so good for the large numbers of others who may spend the rest of their lives incontinent or impotent,

A study in 2004, involving a total of twenty-four thousand patients, found that atenolol did indeed reduce blood pressure but did not reduce heart attacks or fatalities compared with giving no treatment at all.

A study in New Zealand of diabetic patients in 2016 found that the proportion suffering severe complications was 40 percent lower among patients treated by doctors rated high for compassion. As one observer put it, that is “comparable to the benefits seen with the most intensive medical therapy for diabetes.”

I IN 2011, AN interesting milestone in human history was passed. For the first time, more people globally died from non-communicable diseases like heart failure, stroke, and diabetes than from all infectious diseases combined.

He discovered that cultured human stem cells—that is, cells grown in a lab, as opposed to in a living body—can divide only about fifty times before they mysteriously lose their power to go on. In essence, they appear to be programmed to die of old age. The phenomenon became known as the Hayflick limit.

It is a myth, incidentally, that menopause is triggered by women exhausting their supply of eggs. They still have eggs. Not many, to be sure, but more than enough to remain fertile.

Costa Ricans have only about one-fifth the personal wealth of Americans, and have poorer health care, but live longer. Moreover, people in one of the poorest regions of Costa Rica, the Nicoya Peninsula, live longest of all, even though they have much higher rates of obesity and hypertension. They also have longer telomeres. The theory is that they benefit from closer social bonds and family relationships. Curiously, it was found that if they live alone or don’t see a child at least once a week, the telomere length advantage vanishes. It is an extraordinary fact that having good and loving relationships physically alters your DNA.

Alzheimer’s begins with an accumulation of a protein fragment called beta-amyloid in the sufferer’s brain.

Dementias of all types are considerably rarer in people who eat a healthy diet, exercise at least moderately, maintain a sound weight, and don’t smoke at all or drink to excess. Virtuous living doesn’t eliminate the risk of Alzheimer’s, but it does reduce it by about 60 percent.

Agonal breathing, in which the sufferer can’t get enough breath because of a failing heart, may last only for a few seconds, but it can go on for forty minutes or more and be extremely distressing to both victim and loved ones at the bedside. It can be stopped with a neuromuscular blocking agent, but many doctors won’t administer it, because it inevitably hastens death and is therefore thought unethical or even possibly illegal, even though death is just around the corner anyway.