The Body by Bill Bryson — Notes

Sohil Gupta

·

Follow

30 min read

·

Dec 14, 2021

--

Listen

Share

Highlights

1. All the chemicals that make up a human body can be bought in a hardware store for $10.00
2. 59 elements are needed to construct a human being. Six of these — carbon, oxygen, hydrogen, nitrogen, calcium, and phosphorus — account for 99.1 percent of what makes us.
3. The biggest component in any human, filling 61 percent of available space, is oxygen. It may seem a touch counterintuitive that we are almost two-thirds composed of an odorless gas.
4. Skin and hair are made largely of the same stuff: keratin.
5. We don’t have any receptors for wetness. We have only thermal sensors to guide us, which is why when you sit down on a wet spot, you can’t generally tell whether it really is wet or just cold.
6. If you put all Earth’s microbes in one heap and all the other animal life in another, the microbe heap would be twenty-five times greater than the animal one.
7. Brain is 75 to 80 percent water, with the rest split mostly between fat and protein.
8. Over a lifetime, we eat about sixty tons of food, which is equivalent, notes Carl Zimmer in Microcosm, to eating sixty small cars.

1. HOW TO BUILD A HUMAN

1. All the chemicals that make up a human body can be bought in a hardware store for $10.00
2. 59 elements are needed to construct a human being. Six of these — carbon, oxygen, hydrogen, nitrogen, calcium, and phosphorus — account for 99.1 percent of what makes us, but much of the rest is a bit unexpected. Who would have thought that we would be incomplete without some molybdenum inside us, or vanadium, manganese, tin, and copper? Our requirements for some of these, it must be said, are surpassingly modest and are measured in parts per million or even parts per billion. We need, for instance, just 20 atoms of cobalt and 30 of chromium for every 999,999,999½ atoms of everything else.
3. The biggest component in any human, filling 61 percent of available space, is oxygen. It may seem a touch counterintuitive that we are almost two-thirds composed of an odorless gas. The reason we are not light and bouncy like a balloon is that the oxygen is mostly bound up with hydrogen (which accounts for another 10 percent of you) to make water — and water, as you will know if you have ever tried to move a wading pool or just walked around in really wet clothes, is surprisingly heavy. It is a little ironic that two of the lightest things in nature, oxygen and hydrogen, when combined form one of the heaviest, but that’s nature for you. Oxygen and hydrogen are also two of the cheaper elements within you. All your oxygen will set you back just $14 and your hydrogen a little over $26 (assuming you are about the size of Benedict Cumberbatch). Your nitrogen (2.6 percent of you) is a better value still at just forty cents for a body’s worth.
4. You need about thirty pounds of carbon, and that will cost you $69,550. Calcium, phosphorus, and potassium, though needed in much smaller amounts, would between them set you back a further $73,800. Thorium costs over $3,000 per gram but constitutes just 0.0000001 percent of you, so you can buy a body’s worth for thirty-three cents. All the tin you require can be yours for six cents, while zirconium and niobium will cost you just three cents apiece. The 0.000000007 percent of you that is samarium isn’t apparently worth charging for at all.
5. Cadmium is the twenty-third most common element in the body, constituting 0.1 percent of your bulk, but it is seriously toxic. We have it in us not because our body craves it but because it gets into plants from the soil and then into us when we eat the plants. If you are from North America, you probably ingest about eighty micrograms of cadmium a day, and no part of it does you any good at all.
6. Pluck almost any cell from your body, and it will have a million or more selenium atoms in it, yet until recently nobody had any idea what they were there for. We now know that selenium makes two vital enzymes, deficiency in which has been linked to hypertension, arthritis, anemia, some cancers, and even, possibly, reduced sperm counts. So, clearly it is a good idea to get some selenium inside you (it is found particularly in nuts, whole wheat bread, and fish), but at the same time if you take in too much you can irremediably poison your liver.
7. According to the RSC, the full cost of building a new human being, using the obliging Benedict Cumberbatch as a template, would be a very precise $151,578.46. Labor and sales tax would, of course, boost costs further. You would probably be lucky to get a take-home Benedict Cumberbatch for much under $300,000.
8. You blink fourteen thousand times a day — so much that your eyes are shut for twenty-three minutes of every waking day.
9. In the second or so since you started this sentence, your body has made a million red blood cells.
10. Altogether it takes 7 billion billion billion (that’s 7,000,000,000,000,000,000,000,000,000, or 7 octillion) atoms to make you.
11. Your lungs, smoothed out, would cover a tennis court, and the airways within them would stretch nearly from coast to coast.
12. The length of all your blood vessels would take you two and a half times around Earth. The most remarkable part of all is your DNA (or deoxyribonucleic acid). You have a meter of it packed into every cell, and so many cells that if you formed all the DNA in your body into a single strand, it would stretch ten billion miles, to beyond Pluto. Think of it: there is enough of you to leave the solar system. You are in the most literal sense cosmic.
13. The heart of the cell is the nucleus. It contains the cell’s DNA — three feet of it. The reason so much DNA can fit into a cell nucleus is that it is exquisitely thin. You would need twenty billion strands of DNA laid side by side to make the width of the finest human hair. Every cell in your body (strictly speaking, every cell with a nucleus) holds two copies of your DNA. That’s why you have enough to stretch to Pluto and beyond.
14. DNA exists for just one purpose — to create more DNA. Your DNA is simply an instruction manual for making you. A length of DNA is divided into segments called chromosomes and shorter individual units called genes. The sum of all your genes is the genome.
15. DNA is extremely stable. It can last for tens of thousands of years.
16. DNA passes on information with extraordinary fidelity. It makes only about one error per every billion letters copied. Still, because your cells divide so much, that is about three errors, or mutations, per cell division. Most of those mutations the body can ignore, but just occasionally they have lasting significance. That is evolution.
17. What genes specifically do is provide instructions for building proteins. Most of the useful things in the body are proteins. Some speed up chemical changes and are known as enzymes. Others convey chemical messages and are known as hormones. Still others attack pathogens and are called antibodies. The largest of all our proteins is called titin, which helps to control muscle elasticity.
18. All humans share 99.9 percent of their DNA, and yet no two humans are alike. My DNA and your DNA will differ in three to four million places, which is a small proportion of the total but enough to make a lot of difference between us. You also have within you about a hundred personal mutations — stretches of genetic instructions that don’t quite match any of the genes given to you by either of your parents but are yours alone.
19. Only 2 percent of the human genome codes for proteins, which is to say only 2 percent does anything demonstrably and unequivocally practical. Quite what the rest is doing isn’t known. A lot of it, it seems, is just there, like freckles on skin.
20. Suicide by lifestyle takes ages.
21. Five out of every six smokers won’t get lung cancer.
22. Every day, it has been estimated, between one and five of your cells turn cancerous, and your immune system captures and kills them. Think of that.
23. Our bodies are a universe of 37.2 trillion cells operating in more or less perfect concert more or less all the time.

2 THE OUTSIDE: SKIN AND HAIR

1. Beauty is only skin deep, but ugly goes clean to the bone. — DOROTHY PARKER
2. The skin consists of an inner layer called the dermis and an outer epidermis. The outermost surface of the epidermis, called the stratum corneum, is made up entirely of dead cells. It is an arresting thought that all that makes you lovely is deceased. Where body meets air, we are all cadavers. These outer skin cells are replaced every month. We shed skin copiously, almost carelessly: some twenty-five thousand flakes a minute, over a million pieces every hour.
3. Skin and hair are made largely of the same stuff: keratin.
4. Beneath the epidermis is the more fertile dermis, where reside all the skin’s active systems — blood and lymph vessels, nerve fibers, the roots of hair follicles, the glandular reservoirs of sweat and sebum. Beneath that, and not technically part of the skin, is a subcutaneous layer where fat is stored. Though it may not be part of the cutaneous system, it’s an important part of your body because it stores energy, provides insulation, and attaches the skin to the body beneath.
5. Sebum mixes with sweat to form oil on the skin surface. This helps to keep skin supple and to make it inhospitable for many foreign organisms. Sometimes the pores become blocked with little plugs of dead skin and dried sebum in what is known as a blackhead. If the follicle additionally becomes infected and inflamed, the result is the adolescent dread known as a pimple.
6. Meissner’s corpuscles are everyone’s favorites. They detect light touch and are particularly abundant in our erogenous zones and other areas of heightened sensitivity: fingertips, lips, tongue, clitoris, penis, and so on.
7. We don’t have any receptors for wetness. We have only thermal sensors to guide us, which is why when you sit down on a wet spot, you can’t generally tell whether it really is wet or just cold.
8. Women are much better than men at tactile sensitivity with fingers, but possibly just because they have smaller hands and thus a more dense network of sensors. An interesting thing about touch is that the brain doesn’t just tell you how something feels, but how it ought to feel. That’s why the caress of a lover feels wonderful, but the same touch by a stranger would feel creepy or horrible. It’s also why it is so hard to tickle yourself.
9. A sliver of a translucent, one millimeter thick skin is where all the skin color is. That’s all that race is — a sliver of epidermis.
10. “People act as if skin color is a determinant of character when all it is is a reaction to sunlight. Biologically, there is actually no such thing as race — nothing in terms of skin color, facial features, hair type, bone structure, or anything else that is a defining quality among peoples. And yet look how many people have been enslaved or hated or lynched or deprived of fundamental rights through history because of the color of their skin.” — Nina Jablonski
11. Melanin’s production slows dramatically as we age, and as it colors our hair also, which is why older people’s hair tends to turn gray.
12. Melanin is a superb natural sunscreen. It is produced in cells called melanocytes. All of us, whatever our race, have the same number of melanocytes. The difference is in the amount of melanin produced. Melanin often responds to sunlight in a literally patchy way, resulting in freckles, which are technically known as ephelides.
13. light skin may be a consequence of human migration and the rise of agriculture. The argument is that hunter-gatherers got a lot of their vitamin D from fish and game and that these inputs fell sharply when people started growing crops, especially as they moved into northern latitudes. It therefore became a great advantage to have lighter skin, to synthesize extra vitamin D.
14. Vitamin D is vital to health. It helps to build strong bones and teeth, boosts the immune system, fights cancers, and nourishes the heart. It is thoroughly good stuff. We can get it in two ways — from the foods we eat or through sunlight. The problem is that too much UV exposure damages DNA in our cells and can cause skin cancer.
15. Humans have addressed the challenge by evolving a range of skin tones to suit sunshine intensity at different latitudes. When a human body adapts to altered circumstances, the process is known as phenotypic plasticity. We alter our skin color all the time — when we tan or burn beneath a bright sun or blush from embarrassment. The red of sunburn is because the tiny blood vessels in the affected areas become engorged with blood, making the skin hot to the touch. The formal name for sunburn is erythema.
16. Pregnant women frequently undergo a darkening of the nipples and areolae, and sometimes of other parts of the body such as the abdomen and face, as a result of increased production of melanin. The process is known as melasma.
17. To meet dietary requirements from food alone, you would have to eat fifteen eggs or six pounds of swiss cheese every day, or, more plausibly if not more palatably, swallow half a tablespoon of cod liver oil. In America, milk is helpfully supplemented with vitamin D, but that still provides only a third of daily adult requirements. In consequence, some 50 percent of people globally are estimated to be vitamin D deficient for at least part of the year. In northern climes, it may be as much as 90 percent.
18. Hair and eye color don’t affect vitamin D metabolism.
19. If you have blue or green eyes, it’s not because you have more of those colors in your irises than other people but because you simply have less of other colors.
20. Hairless skin is called glabrous, and there isn’t much of it. Our only truly hairless parts are lips, nipples and genitalia, and the bottoms of our hands and feet.
21. The rest of the body is covered with either conspicuous hair, called terminal hair, as on your head, or vellus hair, which is the downy stuff you find on a child’s cheek.
22. Horripilation (Goose Bumps): The erection of hairs on the skin due to cold, fear, or excitement
23. Hair on the head acts as a good insulator in cold weather and a good reflector of heat in hot weather.
24. For facial hair a cycle is normally completed in four weeks, but a scalp hair may be with you for as much as six or seven years. A hair in your armpit is likely to last about six months, a leg hair for two months. Hair grows by one third of a millimeter a day.
25. The textbook name for fingerprints is dermatoglyphics. The plow lines that make up our fingerprints are papillary ridges. They are assumed to aid in gripping, in the way tire treads improve traction on roads.
26. “It is plain old unglamorous sweat that has made humans what they are today.” — Nina Jablonski
27. Chimpanzees have only about half as many sweat glands as we have, and so can’t dissipate heat as quickly as humans can.
28. The loss of most of our body hair and the gain of the ability to dissipate excess body heat through eccrine sweating helped to make possible the dramatic enlargement of our most temperature-sensitive organ, the brain. Sweat helps to make you brainy.
29. Sweating is activated by the release of adrenaline, which is why when you are stressed, you break into a sweat.
30. It is eccrine sweat in your feet — or more correctly the chemical breakdown by bacteria of the sweat in your feet — that accounts for their lush odor. Sweat on its own is actually odorless. It needs bacteria to create a smell. The two chemicals that account for the odor — isovaleric acid and methanediol — are also produced by bacterial actions on some cheeses, which is why feet and cheese can often smell so very alike.
31. Your skin microbes are exceedingly personal. The microbes that live on you depend to a surprising degree on what soaps or laundry detergents you use, whether you favor cotton clothing or wool, whether you shower before work or after. Some of your microbes are permanent residents. Others camp out on you for a week or a month and then, like a wandering tribe, quietly vanish.
32. The problem with antibacterial soaps is that they kill good bacteria on your skin as well as bad.
33. Studies of scratching showed that the most prolonged relief comes from scratching the back but the most pleasurable relief comes from scratching the ankle.
34. About 60 percent of men are “substantially bald” by the age of fifty. One man in five achieves that condition by thirty.

3. MICROBIAL YOU

1. And we are not at the end of the penicillin story. Perhaps we are only just at the beginning. — ALEXANDER FLEMING
2. Eighty percent of the air you breathe is nitrogen.
3. Trillions and trillions of Microbes provide you with about 10 percent of your calories by breaking down foods that you couldn’t otherwise make use of, and in the process extract beneficial nutriments like vitamins B 2 and B 12 and folic acid. Humans produce twenty digestive enzymes, which is a pretty respectable number in the animal world, but bacteria produce ten thousand, or five hundred times as many, according to Christopher Gardner of Stanford University. “Our lives would be vastly less well nourished without them,”
4. E. coli can reproduce seventy-two times in a day, which means that in three days they can rack up as many new generations as we have managed in the whole of human history.
5. A single parent bacterium could in theory produce a mass of offspring greater than the weight of Earth in less than two days. In three days, its progeny would exceed the mass of the observable universe.
6. If you put all Earth’s microbes in one heap and all the other animal life in another, the microbe heap would be twenty-five times greater than the animal one.
7. This is a planet of microbes. We are here at their pleasure. They don’t need us at all. We’d be dead in a day without them.
8. you are likely to have something like 40,000 species of microbes calling you home — 900 in your nostrils, 800 more on your inside cheeks, 1,300 next door on your gums, as many as 36,000 in your gastrointestinal tract.
9. Thin people have more gut microbes than fat people; having hungry microbes may at least partly account for their thinness.
10. Altogether your private load of microbes weighs roughly three pounds, about the same as your brain.
11. Microbiota is considered as one of our organs.
12. Looked at genetically, you have about twenty thousand genes of your own within you, but perhaps as many as twenty million bacterial genes, so from that perspective you are roughly 99 percent bacterial and not quite 1 percent you.
13. Passionate kissing alone, according to one study, results in the transfer of up to one billion bacteria from one mouth to another, along with about 0.7 milligrams of protein, 0.45 milligrams of salt, 0.7 micrograms of fat, and 0.2 micrograms of “miscellaneous organic compounds” (that is, bits of food).
14. 1,415 tiny, mindless entities cause one-third of all deaths on the planet.
15. A virus is a piece of bad news wrapped up in a protein. — Peter Medawar
16. Most viruses infect only bacterial cells and have no effect on us at all. Of the hundreds of thousands of viruses reasonably supposed to exist, just 586 species are known to infect mammals, and of these only 263 affect humans.
17. Ocean viruses alone if laid end to end would stretch for ten million light-years. — Dorothy H. Crawford
18. Surprisingly, the least effective way to spread germs (according to yet another study) is kissing. It proved almost wholly ineffective among volunteers at the University of Wisconsin who had been successfully infected with cold virus. Sneezes and coughs weren’t much better. The only really reliable way to transfer cold germs is physically by touch.
19. The two other forms of microbe that commonly lurk within us are fungi and protists.
20. Fungi is of two types - Mold and yeast
21. All single-celled organisms were called protozoa. Plasmodium protists are the evil little creatures that transfer from mosquitoes into us and give us malaria.
22. The more we expose microbes to antibiotics, the more opportunity they have to develop resistance

4. THE BRAIN

1. The brain is wider than the sky, For, put them side by side, The one the other will include With ease, and you beside. — EMILY DICKINSON
2. Brain is 75 to 80 percent water, with the rest split mostly between fat and protein.
3. Brain has no pain receptors, literally no feelings. It has never felt warm sunshine or a soft breeze. To your brain, the world is just a stream of electrical pulses, like taps of Morse code.
4. Just sitting quietly, doing nothing at all, your brain churns through more information in thirty seconds than the Hubble Space Telescope has processed in thirty years.
5. A morsel of cortex one cubic millimeter in size — about the size of a grain of sand — could hold two thousand terabytes of information, enough to store all the movies ever made, trailers included, or about 1.2 billion copies of this book.
6. The human brain is estimated to hold something on the order of two hundred exabytes of information, roughly equal to “the entire digital content of today’s world.
7. The brain is often depicted as a hungry organ. It makes up just 2 percent of our body weight but uses 20 percent of our energy.
8. In newborn infants, it’s no less than 65 percent. That’s partly why babies sleep all the time — their growing brains exhaust them — and have a lot of body fat, to use as an energy reserve when needed.
9. Your muscles actually use even more of your energy, about a quarter, but you have a lot of muscle; per unit of matter, the brain is by far the most expensive of our organs.
10. Your brain requires only about four hundred calories of energy a day — about the same as you get in a blueberry muffin.
11. Unlike other parts of the body, the brain burns its four hundred calories at a steady rate no matter what you are doing. Hard thinking doesn’t help you slim.
12. Richard Haier used positron emission tomography scanners to find that the hardest-working brains are usually the least productive. The most efficient brains, he found, were those that could solve a task quickly and then go into a kind of standby mode.
13. We use exactly the same components — neurons, axons, ganglia, and so on — as a dog or hamster. Whales and elephants have much larger brains than we have, though of course they also have much larger bodies. But even a mouse scaled up to the size of a human would have a brain just as big, and many birds would do even better.
14. Brain has 86 billion nerve cells, or neurons.
15. Other cells are compact and spherical. Neurons are long and stringy, the better to pass on electrical signals from one to another.
16. Each neuron connects with thousands of other neurons, giving trillions and trillions of connections — as many connections “ in a single cubic centimeter of brain tissue as there are stars in the Milky Way,” to quote the neuroscientist David Eagleman.
17. To survive on Earth, you don’t need to be able to write music or engage in philosophy — you really only need to be able to outthink a quadruped — so why have we invested so much energy and risk in producing mental capacity that we don’t really need?
18. At the top, literally and figuratively, is the cerebrum, which fills most of the cranial vault and is the part that we normally think of when we think of “the brain.” The cerebrum (from the Latin word for “brain”) is the seat of all our higher functions. It is divided into two hemispheres.
19. Each hemisphere of the cerebrum is further divided into four lobes: frontal, parietal, occipital, and temporal.
20. The parietal lobe manages sensory inputs like touch and temperature. The occipital lobe processes visual information, and the temporal lobe principally manages auditory information, though it also helps with processing visual information.
21. The frontal lobe is the seat of the higher functions of the brain — reasoning, forethought, problem solving, emotional control. It is the part responsible for personality.
22. Beneath the cerebrum, at the very back of the head about where it meets the nape of the neck, is the cerebellum (Latin for “little brain”). Although the cerebellum occupies just 10 percent of the cranial cavity, it has more than half the brain’s neurons. It has a lot of neurons not because it does a great deal of thinking but because it controls balance and complex movements, and that requires an abundance of wiring.
23. At the base of the brain, descending from it rather like an elevator shaft connecting the brain to the spine and the body beyond, is the oldest part of the brain, the brain stem. It is the home of our more basic operations: sleeping, breathing, keeping the heart going.
24. Scattered through the brain rather like nuts in a fruitcake are many smaller structures — hypothalamus, amygdala, hippocampus, telencephalon, septum pellucidum, habenular commissure, entorhinal cortex, and a dozen or so others — which are collectively known as the limbic system (from the Latin limbus, meaning “peripheral”).
25. People whose amygdalae are destroyed are left literally fearless, and often cannot even recognize fear in others. The amygdala grows particularly lively when we are asleep, and thus may account for why our dreams are so often disturbing. Your nightmares may simply be the amygdalae unburdening themselves.
26. To help us deal better with this fractional lag, the brain does a truly extraordinary thing: it continuously forecasts what the world will be like a fifth of a second from now, and that is what it gives us as the present. That means that we never see the world as it is at this very instant, but rather as it will be a fraction of a moment in the future. We spend our whole lives, in other words, living in a world that doesn’t quite exist yet.
27. Human memory works like a Wikipedia page. You can go in there and change it, and so can other people. — Elizabeth Loftus
28. Memories are categorized long-term, short-term, and working (for duration) and procedural, conceptual, semantic, declarative, implicit, autobiographical, and sensual (for type).
29. Memories come in two principal varieties: declarative and procedural. Declarative memory is the kind you can put into words — the names of state capitals, your date of birth, how to spell “ophthalmologist,” and everything else you know as fact. Procedural memory describes the things you know and understand but couldn’t so easily put into words — how to swim, drive a car, peel an orange, identify colors.
30. Working memory is where short-term and long-term memories combine. Say you are presented with a mathematical problem to solve. The problem resides in short-term memory — you won’t, after all, need to remember the problem months from now — but the skills necessary to make the computation are kept in long-term memory.
31. Recall memory, which is what you can remember spontaneously — the kinds of things you know when you do a general knowledge quiz — and recognition memory, which is where you are a bit hazy on the substance but can recall the context. Recognition memory is actually useful because it doesn’t clutter the brain with unnecessary details but does help us to remember where we can find those details if we should need them again.
32. Short-term memory is really short — no more than half a minute or so for things like addresses and phone numbers. (If you can still remember something after half a minute, it is no longer technically a short-term memory. It’s long term.) Most people’s short-term memory is pretty abysmal. Six random words or digits is about all that most of us can reliably retain for more than a few moments.
33. Hippocampus has a central role in laying down memories.
34. Higher processes — thinking, seeing, hearing, and so on — happen right at the surface, in the four-millimeter-thick sheath of the cerebral cortex.
35. The cerebral cortex, is the brain’s celebrated gray matter. Beneath it is the much greater volume of white matter, which is so called because the neurons are sheathed in a pale fatty insulator called myelin, which greatly accelerates the speed at which signals are transmitted. Both white matter and gray matter are misleadingly named. Gray matter isn’t terribly gray in life, but has a pinkish blush. It only becomes conspicuously gray in the absence of blood flow and with the addition of preservatives. White matter is also a posthumous attribute because the pickling process turns the myelin coatings on its nerve fibers a luminous white.
36. The idea that we use only 10 percent of our brains is a myth
37. A teenager’s brain is only about 80 percent finished. Although most of the growth of the brain occurs in the first two years and is 95 percent completed by the age of ten, the synapses aren’t fully wired until a young person is in his or her mid- to late twenties.
38. The nucleus accumbens, a region of the forebrain associated with pleasure, grows to its largest size in one’s teenage years. At the same time, the body produces more dopamine, the neurotransmitter that conveys pleasure, than it ever will again.
39. Everybody has heard of neurons, but not so many are familiar with the other main brain cells, glia or glial cells, which is a little odd because they outnumber neurons by ten to one. Glia (the word means “glue” or “putty”) are the cells that support neurons in the brain and central nervous system.
40. Once you pass early childhood, you have all the brain cells you are ever going to have.
41. The heart pumps, the lungs inflate and deflate, the intestines quietly ripple and gurgle, but the brain just sits pudding-like, giving away nothing.

12. THE IMMUNE SYSTEM

1. We have some three hundred different types of immune cells at work within us.
2. If you are stressed or exhausted, you are much more likely to suffer an infection
3. At the heart of the system are five types of white blood cells: lymphocytes, monocytes, basophils, neutrophils, and eosinophils.
4. Lymphocytes are of two principal types: B cells and T cells. B cells are produced in Bone Marrow, and T cells in Thyme organ
5. T cells are a kind of elite corps in the immune system.
6. T cells subdivide into two further categories: helper T cells and killer T cells. Helper T cells help other immune cells act, including helping B cells produce antibodies.
7. 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.
8. Some infectious agents, like E. coli and salmonella, can trick the immune system into attacking the wrong organisms.
9. 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.
10. When WBCs 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.
11. Inflammation is a tricky thing. Too much and it destroys neighboring tissues and can result in unnecessary pain, but too little and it fails to stop infection. Faulty inflammation has been linked to all kinds of maladies, from diabetes and Alzheimer’s disease to heart attacks and strokes.
12. Sometimes 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.
13. As of late 2018, 114,000 people were on transplant waiting lists in the United States. A new person joins the list every ten minutes, and twenty people a day die before a donated organ can be found. People on dialysis live an extra eight years on average, but that rises to twenty-three years with a transplant.
14. About a third of kidney transplants come from living donors (typically a close relative), but all other transplanted organs are from deceased donors, which is a real challenge.
15. The median waiting time today for a kidney transplant in the United States is 3.6 years, up from 2.9 years in 2004, but many people can’t wait that long. In the United States, seven thousand people a year on average die before they can receive a transplant.
16. Altogether humans are afflicted by some fifty types of autoimmune diseases, and the numbers are rising.
17. 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.
18. The richer the country, the more allergies its citizens get.
19. Hygiene hypothesis: The idea is that children in the developed world grow up in much cleaner environments than children of earlier ages did, and so don’t develop resistance to infection as well as those who have a more intimate contact with dirt and parasites.

14. FOOD, GLORIOUS FOOD

1. 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.
2. We cannot make use of cellulose, which is what plants primarily consist of.
3. A cooked potato is about twenty times more digestible than a raw one.
4. Cooking frees up a lot of time for us. Other primates spend as many as seven hours a day just chewing. We don’t need to eat constantly to ensure our survival.
5. Too much or too little iron both provide the same symptom, lethargy. “Too much iron in the form of supplements can accumulate in our tissues causing our organs literally to rust,”
6. Potassium helps to keep your heart beating smoothly and your blood pressure within tolerable limits.

PROTEINS

1. 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.
2. 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

1. 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. Although all are sugars, not all are sweet. Some, like the starches found in pasta and potatoes, are too big to activate the tongue’s sweet detectors
2. All carbohydrates in the diet come from plants, with one conspicuous exception: lactose, from milk.
3. A 150-gram serving of white rice or a small bowl of cornflakes will have the same effect on your blood glucose levels as nine teaspoons of sugar.

FATS

1. When fats are broken down in the body, they are teamed up with cholesterol and proteins in a new molecule called lipoproteins, which travel through the body via the bloodstream. Lipoproteins come in two principal types: high density and low density. Low-density lipoproteins are the ones frequently referred to as “bad cholesterol” because they tend to form plaque deposits on the walls of blood vessels.
2. About 7 percent of Cholestrol — floats about in the bloodstream. Of that 7 percent, one-third is “good” cholesterol and two-thirds is “bad.”
3. Fiber is the material in fruits, vegetables, and other plant foods that the body cannot fully break down. It contains no calories and no vitamins, but it helps to lower cholesterol and slows the rate at which sugar gets into the bloodstream and is then turned into fat by the liver, among many other benefits.
4. The body burns some of the fat we consume for energy, but a good deal of the rest is sent off to tens of billions of tiny storage terminals called adipocytes, which exist all over the body.
5. Depending on where the fat ends up, it is known as subcutaneous (beneath the skin) or visceral (around the belly). For complex chemical reasons, visceral fat is much worse for you than the subcutaneous kind.
6. Animal fats tend to be saturated and vegetable fats to be unsaturated
7. Also known as hydrogenated oils, trans fats are much worse for your heart than any other kind of fat. They raise levels of bad cholesterol, lower levels of good cholesterol, and damage the liver.
8. We consume about two and a half quarts of water a day.
9. Drinking too much water can actually be dangerous. Normally, your body manages fluid balance very well, but occasionally people take in so much water that the kidneys cannot get rid of it fast enough and they end up dangerously diluting the sodium levels in their blood, setting off a condition known as hyponatremia
10. Over a lifetime, we eat about sixty tons of food, which is equivalent, notes Carl Zimmer in Microcosm, to eating sixty small cars.
11. One chocolate chip cookie a week, in the absence of any offsetting extra exercise, will translate into about two pounds of extra weight a year.
12. The French eat more cheese and drink more wine than almost anybody else on Earth and yet have some of the lowest rates of heart disease
13. The official guidance in most countries is that fats should account for no more than 30 percent of a person’s daily diet, and saturated fats no more than 7 percent.
14. A forty-year-old man who eats a hamburger every day will knock a year off his life expectancy.
15. Sugar has 16 calories per teaspoon.
16. Three apples would give you just as much sugar but compensate by also giving you vitamins, minerals, and fiber, not to mention a greater feeling of satiation.
17. It is often written that eating a daily helping of processed meat increases your risk of colorectal cancer by 18 percent, which is doubtless true. But as Julia Belluz of Vox has pointed out, “A person’s lifetime risk of colorectal cancer is about 5 percent, and eating processed meat every day appears to boost a person’s absolute risk of cancer by 1 percentage point, to 6 percent (that’s 18 percent of the 5 percent lifetime risk).”

15. THE GUTS

1. Your alimentary canal is about forty feet long if you are an average-sized man. The surface area of all that tubing is about half an acre.
2. For a man, the average journey time from mouth to anus is fifty-five hours. For a woman, typically, it is more like seventy-two.
3. Each meal you eat spends about four to six hours in the stomach, a further six to eight hours in the small intestine, where all that is nutritious (or fattening) is stripped away and dispatched to the rest of the body to be used or, alas, stored, and up to three days in the colon, which is essentially a large fermentation tank where billions and billions of bacteria pick over whatever the rest of the intestines couldn’t manage — fiber mostly.
4. Many people have had their stomachs removed without serious consequence. The real digestion and absorption — the feeding of the body — happens further down.
5. The stomach of a big dog will hold up to twice as much food as yours does.
6. The rumblings of your gut, incidentally, come mostly from the large intestine, not the stomach. The technical term for gut rumblings is “borborygmi”
7. One thing the stomach does do is kill off many microbes, by soaking them in hydrochloric acid. “Without your stomach, a lot more of what you ate would make you ill,”
8. E. coli in your colon produces vitamin K for you.
9. Responsibility for food safety is split among a raft of federal agencies in America in a way that rather defies logic. The Food and Drug Administration is responsible for the skin of sausages, but the Food Safety and Inspection Service is responsible for what goes inside them
10. Most nausea-inducing microbes need time to proliferate inside you before they make you sick, mostly 24 hours.
11. “People tend to blame the last thing they ate, but it’s probably the thing before the last thing they ate”
12. The largest source of food-borne illness is not meat or eggs or mayonnaise, as commonly supposed, but green leafy vegetables. They account for one in five of all food illnesses.
13. Appendix serves as a reservoir for gut bacteria.
14. The large intestine (also known as bowel/colon) is a kind of fermentation tank, home of feces, flatus, and all our microbial flora.
15. Adults in the West produce about 200 grams of feces a day — a little under half a pound, about 180 pounds a year, 14,000 pounds in a lifetime.
16. Stools consist in large part of dead bacteria, undigested fiber, sloughed-off intestinal cells, and the residues of dead red blood cells.
17. Every gram of feces you produce contains 40 billion bacteria and 100 million archaea.
18. Stool samples taken two days apart can give strikingly different results. Even samples taken from two ends of the same stool can seem to come from two different people
19. Nearly all cancer that occurs in the gut is found in the large intestine and almost never in the small intestine.
20. Mice get cancer in the small intestine but not in the colon. But if you give them a Western-style diet, that reverses. It is the same for Japanese people when they move to the West and adopt a Western lifestyle. They get less stomach cancer, but more colon cancer.
21. E. coli has become the most studied microbe on the planet. Carl Zimmer, has written a fascinating book, Microcosm, on this bacillus.
22. Two strains of E. coli have more genetic variability than all the mammals on Earth put together.
23. Flatus (farts) consists primarily of carbon dioxide (up to 50 percent), hydrogen (up to 40 percent), and nitrogen (up to 20 percent)
24. About a third of people produce methane, a notorious greenhouse gas, while two-thirds produce none at all.
25. The smell of a fart is composed largely of hydrogen sulfide, even though hydrogen sulfide accounts for only about one to three parts per million of what is expelled.

21. WHEN THINGS GO VERY WRONG: CANCER

1. Pneumonia is the ninth most common cause of death. Heart disease number one, and cancer second.
2. Today some 40 percent of us will discover we have cancer at some point in our lives.
3. Half of men over sixty and three-quarters over seventy, for instance, have prostate cancer at death without being aware of it. It has been suggested, in fact, that if all men lived long enough, they would all get prostate cancer.
4. They divide without limit.
5. They grow without direction or influence from outside agents like hormones.
6. They engage in angiogenesis, which is to say they trick the body into giving them a blood supply.
7. They disregard any signals to stop growing.
8. They fail to succumb to apoptosis, or programmed cell death.
9. They metastasize, or spread to other parts of the body.
10. What it comes down to really is cancer is, appallingly, your own body doing its best to kill you. It is suicide without permission.
11. Cancer cells are just like normal cells except that they are proliferating wildly. Because they are so seemingly normal, the body sometimes fails to detect them and doesn’t invoke an inflammatory response as it would with a foreign agent. That means that most cancers in their early stages are painless and invisible. It is only when tumors grow big enough to press on nerves or form a lump that we become aware that something is wrong. Some cancers can quietly accrete for decades before they become evident. Others never become evident at all.
12. Even when seemingly defeated, cancer may leave behind “sleeper” cells that can lie dormant for years before springing to life again. Above all, cancer cells are selfish. Normally, human cells do their job, then die on command when instructed to by other cells for the good of the body. Cancer cells don’t.
13. “They have evolved to avoid detection. They can hide from drugs. They can develop resistance. They can recruit other cells to help them. They can go into hibernation and wait for better conditions. They can do any number of things that make it hard for us to kill them.”
14. 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.
15. Between birth and the age of forty, men have just a one in seventy-one chance of getting cancer and women one in fifty-one, but over sixty the odds drop to one in three for men and one in four for women. An eighty-year-old person is a thousand times more likely than a teenager to develop cancer.
16. mustard gas dramatically slowed the creation of white blood cells in those exposed to it. From this, it was realized that some derivative of mustard gas might be useful in treating some cancers. Thus was born chemotherapy.