The Body

Bill Bryson

GENRE: Health & Fitness

PAGES: 464

COMPLETED: August 6, 2023

RATING:

Short Summary

Bill Bryson takes readers through a head-to-toe tour of the human body — how it functions, its remarkable ability to heal itself, and the ways it can fail. The Body is packed with interesting facts about the various elements of the human body, from the brain and heart to the spleen, kidneys, and more.

Key Takeaways

Miraculous Body — The human body is miraculous, and we completely take it for granted. The way the various organs of the body communicate, sync, and work together to keep us alive and healthy is remarkable. The mind and body somehow find a way to keep us going even when we’re feeding it like crap and treating it like crap.

Microbes & Bacteria — We are literally covered in bacteria. Huge swarms of good and bad microbes are in and around us constantly. In 2016, researchers concluded that each of us contains about 30 trillion human cells and between 30-50 trillion bacterial cells, so we have almost an equal number of human and bacterial cells. We need these microbes in order to survive — they do some really important things for us like help digest food, protect against infection, and maintain reproductive health.

Brain Power — Your brain literally constructs your world. To your brain, the world is just a stream of electrical pulses, and, somehow, out of this neutral information it creates for you a vibrant, three-dimensional, sensually engaging universe. Your brain is you. It is one of the most mysterious and amazing things in the world.

Favorite Quote

“The main thing to bear in mind is that carbohydrates, upon being digested, are just more sugar — often quite a lot more. That means that 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.”

Book Notes

Ch. 1: How to Build a Human

Building a Human — In the end, we are just a pile of everyday elements and “stuff. According to the Royal Society of Chemistry, buying the elements needed to build a human would cost you $151,578.46. About 59 elements are needed to construct a human being. About 24 of these elements are knows as essential elements, meaning we can’t do without them. Six of these elements account for 99.1% of what makes us. The big six are:
- Carbon
- Oxygen
- Hydrogen
- Nitrogen
- Calcium
- Phosphorous
- Quote (P. 4): “That is unquestionably the most astounding thing about us — that we are just a collection of inert components, the same stuff you would find in a pile of dirt.”
Oxygen, Hydrogen, and Water — The biggest component in all humans is oxygen, which fills 61% of available space in the body. Literally 2/3 of us is composed of an odorless gas. The reason we aren’t light and bouncy like a balloon is that the oxygen is mostly attached at the hip with hydrogen (which accounts for 10% of a human) to make water, and water is surprisingly heavy (if you’ve worn wet clothes, you know water weighs a lot).
- Quote (P. 2): “It’s 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.”
Interesting Fact — We blink 14,000 times per day, enough that we have our eyes shut for 23 minutes every day just from blinking.
Interesting Fact — Every second your body creates a million red blood cells. They speed around the body and run through your veins, keeping you alive. Each red blood cell will travel around your body 150,000 times delivering oxygen to your cells. Then they get killed off in favor of newer, faster red blood cells.
Cells — The basic unit of life is the cell. Our bodies are a universe of about 37.2 trillion cells operating in almost perfect harmony all the time. Cells are little compartments. These compartments are filled with things like ribosomes and proteins, DNA, RNA, mitochondria, and more. All of these components bump and jostle with each other inside the cells, like a bunch of bumper cars. The contents of the cell respond to signals from each other to produce coordinated action across the cell and with other cells in the body.
- The Nucleus & DNA — This is the heart of the cell. It contains the cell’s DNA. Every cell nucleus contains three feet of DNA, which is super thin and is simply an instruction manual for making you. DNA is divided into segments called chromosomes and shorter units called genes. Remarkably, DNA lasts for tens of thousands of years, long after you’re gone. That’s what allows modern scientists to discover things about the distant past. It’s remarkable to think that your current DNA and genes are a reflection of your ancestors’ development since life started three billion years ago. For you to be here now, every one of your ancestors had to successfully pass on their genetic material to a new generation before dying. That’s quite a chain of success.
- Genes — Within DNA are your genes. Genes 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 changes and are called hormones. Others attack bad stuff in the body and are called antibodies. Interestingly, all humans share 99.9% of their DNA, yet no two humans are alike. There are 3-4 million places in our DNA where everybody’s genes are different, and that’s why we are all different. You also have about 100 personal mutations — stretches of genetic instructions that don’t match any of the genes given to you by your parents.
- Bad Cells — Cells replicate constantly, and it has been estimated that every day between one and five of your cells turn cancerous before your immune system captures and kills them. That means that a couple dozen times a week, and over a thousand times a year, you get the most dreaded disease of our age and your body saves you. Wild.
Chapter Takeaway — Life is miraculous. The way the body works together to keep you up and running is truly remarkable. We take it for granted, but the human body is a gift.

Ch. 2: The Outside - Skin and Hair

The Skin: Our Largest Organ — Surprisingly, the skin is our largest organ. It keeps our insides in and bad things out. It cushions blows. It gives us our sense of touch, bringing us pleasure and warmth and pain and nearly everything else that makes us vital. It produces melanin to shield us from the sun’s rays. It repairs itself when we abuse it. Depending on how tall and wide you are, your skin weigh about 10-15 pounds on its own. The skin consists of two layers:
- Epidermis (Outer Layer) — Interestingly, the very outermost surface of the epidermis is made up entirely of dead cells. These dead outer skin cells are replaced every month; we shed skin like crazy. We shed 25,000 flakes a minute, over a million pieces per hour. If you run your finger along a dusty shelf, you are in large part engaging with your former self in the form of dead skin cells that you’ve shed.
- Dermis (Inner Layer) — Beneath the epidermis is the dermis, where the skin’s active systems like blood and lymph vessels, nerve fibers, the roots of hair follicles, and sweat glands reside.
Meissner’s Corpuscles — Packed into the dermis are a variety of receptors that keep us in touch with the world by detecting pain, pleasure, and feeling. Everyone’s favorite are the Meissner’s corpuscles, which detect light touch and are located in areas of our body that are particularly sensitive to touch — fingertips, lips, tongue, private parts.
Melanin — Skin color is derived from a variety of pigments, and there are over 120 genes involved in pigmentation. The most important pigment by far is a molecule known as melanin. It’s almost like a natural sunscreen for your skin — it absorbs harmful UV rays and protects cells from damage from UV light exposure by tanning skin that is exposed to sunlight. But it doesn’t just color skin; it is heavily involved in many other key areas like hair and eye color. One of the reasons our hair turns gray as we age is that our levels of melanin in the body drop a lot as we get older.
- Quote (P. 15): “It (melanin) doesn’t just color skin. It gives birds the color of their feathers, fish the texture and luminescence of their scales, squid the purply blackness of their ink. It is even involved in making fruits go brown. In us, it also colors our hair. Its production slows dramatically as we age, which is why older people’s hair tends to turn gray.”
Vitamin D — Vitamin D is vital to health. It helps build strong bones and teeth, boosts the immune system, fights cancer, and helps the heart. 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. When we get a sunburn, the tiny blood vessels in the affected areas become swell with blood and make the skin hot to the touch. Most people do not get enough Vitamin D — about 50% of people globally are deficient.
Skin: Hair and Hairless — Skin comes in two varieties: with hair and without. There isn’t much truly hairless skin on our body; just our lips, nipples, private part, and the bottoms of our hands and feet. Everything else has hair follicles. We’ve evolved to this point of being mostly hairless — we used to be covered in hair. Every hair on your body had a growth cycle, with a growing and resting phase. Scalp hair has a cycle of 6-7 years, but it usually falls out sooner, which is fine because our hair cycles are staggered.
Sweat Glands — Sweating is a crucial part of being human. Because most other animals have far fewer sweat glands on their skin than we do, they cool themselves by panting (think: dog). We, on the other hand, are able to seep watery fluids (sweat) onto our nearly bare skin via our many sweat glands, which cools the body and turns us into a living air conditioner. There are two types of sweat glands:
- Eccrine — These are far more numerous and produce the watery sweat that dampens your shirt on a hot day or on a run.
- Apocrine — These are far less numerous and are found mostly in the groin and armpit areas, which is why they produce a thicker, sticker sweat.
We Sweat… A Lot — We are always sweating. Even as we rest, we sweat. But add in physical exercise and we drain our body’s water supply very fast. That’s why we have to stay hydrated, especially when it’s hot and/or we’re engaged in physical activity. Sweat is 99.5% water. The rest is half salt and half other chemicals. Sweating is activated by the release of adrenaline, which is why you break into a sweat when you’re stressed. Interestingly, unlike the rest of the body, the palms don’t sweat in response to physical exertion or heat, but only from stress. That’s why palm sweat is measured in lie detector tests.
- Quote (P. 23): “According to Peter Stark in Last Breath: Cautionary Tales from the Limits of Human Endurance, a man who weighs 155 pounds will contain a little over forty-two quarts of water. If he does nothing at all but sit and breathe, he will lose about one and a half quarts of water per day through a combination of sweat, respiration, and urination. But if he exerts himself, that rate of loss can shoot up to one and a half quarts per hour. That can quickly become dangerous. In grueling conditions — walking under a hot sun, say — you can easily sweat away ten and a half to twelve and a half quarts of water in a day. No wonder we need to keep hydrated when the weather is hot. Unless the loss is halted or replenished, the victim will begin to suffer headaches and lethargy after losing just three to five quarts of fluid. After six or seven quarts of unrestored loss, mental impairment starts to become likely. (That is when dehydrated hikers leave a trail and wander into the wilderness.) If the loss gets much above ten and a half quarts for a 155-pound man, the victim will go into shock and die.”
  - Takeaway — We sweat a lot! Stay hydrated. It’s crucial to constantly replenish your body’s water supply.
- Quote (P. 23): “Although salt is only a tiny part of your overall sweat, you can lose as much as three teaspoonfuls of it in a day in hot weather, which can be a dangerously high amount, so it is important to replenish salt as well as water.”
Microbes… Ew — You have about 200 different types of microbes, or bacteria, living on your skin. Some are on you for a very long time, while others camp out on your skin for a few weeks and then vanish. There are good and bad bacteria’s living in your skin. It’s not easy to sanitize yourself; to make one’s hands clean after a medical examination requires washing them carefully for over a minute. This is hard to accomplish for doctors who are always on the run to a new patient. This is a big part of why every year over 2 million Americans pick up a serious infection in the hospital. Bacteria is on all of us and it’s not always easy to get rid of bad bacteria.
Chapter Takeaway — The skin is very impressive. It’s our largest organ, and the outside of it is made up of dead cells.

Ch. 3: Microbial You

Nitrogen & Breathing — When you take a deep breath, you likely assume you are filling your lungs with a full inhale of oxygen. Not really. About 80% of the air you breathe is nitrogen, the most abundant element in the atmosphere. About 20% is oxygen, and that oxygen moves to your blood. Nitrogen is vital to our existence, but, unlike oxygen, it doesn’t interact with other elements. When you take a breath, the nitrogen goes into your lungs and straight back out again, like a bad shopper who has wandered into the wrong store. For nitrogen to be useful to us, it must be converted into other forms, like ammonia, and bacteria is what does that job for us.
Microbes — Microbes are a collection of bacteria, viruses, fungi, etc. that live on and inside of you. There are trillions of tiny, microscopic living microbes that call you home. We need them to survive — they do some really important things for us like help digest food, protect against infection, and maintain reproductive health. The average bacterium is extremely light and lives for no more than 20 minutes, but put together they are formidable. They reproduce extremely fast, which is how they stick around. They are also very adaptable — they are able to swap genes like Pokémon cards and pick up genes from dead neighbors. All of this allows them to adapt to whatever nature throws at them.
- Quote (P. 29): “What can be said is that as you sit here now, 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… That is, of course, just the numbers of species. In terms of individual microbes, the number is beyond imagining, never mind counting: it’s in the trillions. Altogether, your private load of microbes weighs roughly three pounds, about the same as your brain. People have even begun describing our microbiota as one of our organs.”
- Quote (P. 29): “Make no mistake. 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.”
Human vs. Bacterial Cells — In 2016, researchers concluded that each of us contains about 30 trillion human cells and between 30-50 trillion bacterial cells (depending on a lot of factors like health and diet), so we have almost an equal number of human and bacterial cells. That said, human cells are much bigger in size and are far more complex in what they do.
Bad Microbes — There are good microbes and bad microbes. Luckily, most microbes have nothing to do with us. Most live on or within is, but don’t do any harm. Only a tiny portion of microbes have been known to make us ill. These are bad microbes. Of the almost million microbes that have been discovered, only 1,415 are known to cause disease in humans. On the other hand, that’s 1,415 ways to be unwell, and all together those 1,415 bad bacteria cause 1/3 of all deaths globally.
Viruses — A virus is a type of microbe that is extremely small and is not quite living but is by no means dead. Outside of living cells, viruses are just things. They don’t move or eat or breathe — we must go out and collect them off of door handles, or handshakes, or when we draw in air via the breath. That’s how we get viruses. They are basically lifeless things, but they spring to life and reproduce quickly when put into a living cell. Most viruses only infect our bacterial cells (not our human cells) and usually don’t cause us any harm. Of the hundreds of thousands of viruses, only 263 affect humans. One researcher found that the average person harbors 174 species of virus, and ocean viruses alone if laid end to end would stretch 10 million light-years. Viruses become a problem when they are one of the 263 that impact humans and they infect us.
Common Cold — This is the most common virus we see and experience. The common cold is not a single illness but rather a family of symptoms generated by many different viruses. There are hundreds of varieties of these common cold viruses, which is why we never develop enough immunity to stop them all and we continue to develop colds here and there throughout our life. It’s nasty how easily a common cold virus is transferred onto furniture, doorknobs, etc., but the only way to reliably transfer cold germs is by touch.
- Quote (P. 35): “A survey of subway trains in Boston found that metal poles are a fairly hostile environment for microbes. Where microbes thrive is in the fabrics on seats and on plastic handgrips. The most efficient method of transfer for germs, it seems, is a combination of folding money and nasal mucus. A study in Switzerland in 2008 found that flu virus can survive on paper money for two and a half weeks if it is accompanied by a microdot of snot. Without snot, most cold viruses could survive on folding money for no more than a few hours.”
Alexander Fleming & Penicillin — In 1928, Alexander Fleming accidentally discovered the antibiotic penicillin. This was the first antibiotic ever discovered. While he was away on vacation, some mold from the genus Penicillium drifted into his lab and landed on a Petri dish containing a certain bacteria he was observing. The mold had slowed the bacteria’s growth. When he returned, Fleming realized the mold had killed some of the bacteria in the dish and decided to try to convert his findings into a useful medicine (penicillin). Fleming would later receive 189 honors from around the world for his discovery, including a Nobel Prize in 1945.
Ernst Chain & Penicillin — Because Fleming had other big things he was focused on, other researchers like the German Ernst Chain picked up some of the work on penicillin. In the 1930s, Chain experimented with penicillin at Oxford in England and found that it killed bad bacteria and viruses in mice without any side effects. Oxford then dedicated a ton of resources to growing the Penicillium mold and extracting penicillin from it. By 1941, they had enough penicillin to use the drug on a man who was battling a severe virus that had taken his eye. The penicillin worked, but they didn’t have enough to keep giving him and he later died.
The United States & Penicillin — Because penicillin was so hard to produce, the U.S. ended up taking on the challenge at a research facility in Illinois. There, a lab assistant named Mary Hunt randomly found a weird mold on a cantaloupe she had bought at a grocery store. They scraped off the mold and tested it. That mold proved to be 200 times more potent than anything else previously tested and allowed the U.S. to produce 100 billion units of penicillin a month. Every bit of penicillin made since that day is descended from that single random cantaloupe.
Antibiotics: Collateral Damage & Resistance — Although antibiotics like penicillin are outstanding and help stop many bad viruses and bacteria, there are some downsides associated with them.
- Collateral Damage — The first is that antibiotics attack a broad spectrum of bacteria, both good and bad microbes. They don’t target the harmful bacteria exclusively. They’re almost like a hand grenade; everything in the area (good or bad) is getting blown up. As a result, you are inflicting unnecessary collateral damage on microbes that are beneficial, and growing research shows that some of the good bacteria may never recover.
- Resistance — The more we expose microbes to antibiotics, the more opportunity they have to develop resistance to the medicine. In 1945, a typical case of pneumonia could be knocked out with 40,000 units of penicillin. Today, because of increased resistance, it can take more than 20 million units per day to achieve the same result. On some diseases, penicillin is no longer effective. As a result, the death rate for infectious diseases has been climbing and is back around levels from 40 years ago. What’s worse is that antibiotics are often prescribed when they aren’t needed and farm animals are given antibiotics to fatten them, meaning Americans consume secondhand antibiotics through their food. All of this adds to antibiotic resistance.
- Slowed Research — From 1950-1990, three new antibiotics were introduced every year. Today, we have one every other year. It’s incredibly expensive to develop new antibiotics today, and antibiotics last only a few weeks. Pharmaceutical companies now prefer to focus on developing other drugs like statins and antidepressants that can be taken regularly rather than a few weeks. All but two of the 18 largest pharmaceutical companies in the world have given up the search for new antibiotics. All of this means our arsenal of drugs to treat bacterial infections has been declining while we are simultaneously becoming more resistant to the antibiotics currently available.
Chapter Takeaway — Weird species of microbes in the form of bacteria and viruses are on and inside us 24/7. Some microbes are actually beneficial. We are becoming alarmingly resistant to antibiotics, and the search for new antibiotics has slowed significantly.

Ch. 4: The Brain

Brain Power — The human brain is maybe the most extraordinary thing in the universe. Physically, it’s 75-80% water and extremely soft. It sits inside your head in silence and darkness, like a dungeoned prisoner. It has no pain receptors, literally no feelings. Altogether the human brain is estimated to hold around 200 exabytes of information.
- Quote (P. 49): “To your brain, the world is just a stream of electrical pulses, like taps of Morse code. And out of this bare and neutral information it creates for you — quite literally creates — a vibrant, three-dimensional, sensually engaging universe. Your brain is you. Everything else is just plumbing and scaffolding.”
- Quote (P. 49): “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. 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.”
The Brain: A Hungry Organ — The brain consists of just 2% of our body weight but uses 20% of our energy. It uses 65% of energy in infants, which is why babies sleep all the time — their growing brains exhaust them. Your brain requires about 400 calories per day, about as many as you get in a blueberry muffin. It churns out that 400 calories at a steady rate no matter what you’re doing. Hard thinking. No thinking. Doesn’t matter.
Neurons — The brain has about 86 billion neurons, or nerve cells. These neurons extend out and connect with each other in a process referred to as “synaptic entanglement.” It is in this synaptic entanglement that our intelligence lies, not in the number of neurons, as was once thought.
Parts of the Brain: The Cerebrum — The brain essentially divides into three sections. At the top is the cerebrum, which is the part we normally think of when we think of “the brain.” The cerebrum stores all of our higher functions and is divided into two hemispheres, each of which controls and regulates one side of the body. The cerebrum is where our thinking, hearing, and seeing goes on and is often referred to as the cerebral cortex. Oddly, the right hemisphere controls the left side of the body. And vice versa. Each hemisphere of the cerebrum is then divided into four lobes:
- Frontal — This is where the majority of the higher functions of the brain rest. The frontal lobe controls reasoning, forethought, problem solving, emotional control, speech, and so on. It is the part responsible for personality and who we are.
- Parietal — Manages sensory inputs like touch and temperature
- Occipital — Processes visual information
- Temporal — Manages sounds and other auditory information
Parts of the Brain: The Cerebellum — The cerebellum is at the very back of the head. It has a ton of neurons, not because it does a lot of thinking but because it controls balance and complex movements. These responsibilities require a lot of wiring.
Parts of the Brain: The Brain Stem — At the base of the brain is the brain stem. It is the home of our more basic operations: sleeping, breathing, keeping the heart going. It is central to our existence.
Parts of the Brain: The Limbic System — Scattered through the brain like nuts in a fruitcake are many smaller structures — the hypothalamus, amygdala, hippocampus, telencephalon, septum pellucidum, habenular commissure, entorhinal cortex, and a dozen or so others — which are collectively known as the limbic system. Despite their obscurity and modest dimensions, the structures of the limbic system have a fundamental role in our happiness by controlling and regulating basic processes like memory, appetite, emotions, drowsiness and alertness, and the processing of sensory information. A few details on some of these include:
- Hypothalamus — This is the size of a peanut and controls much of the most important chemistry of the body. It regulates sexual function, controls hunger and thirst, monitors blood sugar and salts, and decides when you need to sleep.
- Hippocampus — This is central to memory. In one experiment in the mid-1950s, surgeons drilled into the skull of Henry Moliason to remove part of his hippocampus in an attempt to stop his severe seizures. It worked, but he basically completely lost his memory.
- Amygdala — This specializes in handling intense and stressful emotions — fear, anger, anxiety, phobias of all types. 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.
The Brain & Sight — The eyes send a hundred billion signals to the brain every second. When you “see” something, only about 10% of the information comes from the optic nerve. Other parts of your brain have to deconstruct the signals — recognize faces, interpret movements, identify danger, etc. In other words, the biggest part of seeing isn’t receiving visual images; it’s making sense of them. But for each visual input, there’s a slight lag from eye to brain.
- Quote (P. 55): “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.”
The Brain & Memory — The brain breaks every memory into its component parts — names, faces, locations, contexts, how a thing feels to the tough — and sends the parts to different places, then calls then back and reassembles them when the whole is needed again. Fundamentally, however, memories come in three varieties:
- Declarative — Declarative memory is the kind you can put into words: the names of state capitals, your date of birth, how to spell words, and everything else you know as a fact.
- Procedural — 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.
- Recognition — Recognition memory is where you are a bit hazy on the substance but can recall the context of something. Recognition memory explains why so many of us struggle to remember the contents of a book but can often recall where we read the book and the color or design of the cover.
Brain Development — The brain isn’t fully developed until your mid-to-late 20s. Up until that point, you are still developing neurons and the neurons are still going through synapses (connecting with each other). That said, the majority of your neurons are created by the end of childhood. When a person has a stroke or develops some other brain-related disease, he/she loses neurons in the brain and they can’t be re-created.
Lobotomy — A lobotomy is a type of psychosurgery that was used to treat mental health conditions such as mood disorders and schizophrenia. The surgeries involved physically removing or altering part of the brain. These are no longer a thing, but it’s wild that they used to do this in the 1800s and early 1900s. It’s true that removing part of the brain seems to significantly alter personality and mood, but this type of surgery is very reckless. Doctors used to stick ice picks up a patient’s eye socket to scrape away at their brain. These surgeries did a lot of harm to people, most notably Rosemary Kennedy, sister of former President John F. Kennedy.
Interesting Fact — As recently as 1956, it was illegal in 17 states for people with epilepsy (seizures) to marry. These laws were later repealed in 1980. Epilepsy is caused by misfiring of neurons in the brain.
Chapter Takeaway — The brain is both marvelous and mysterious. It is an incredibly complex organ, but it is maybe the most miraculous thing in life. What it can do is incredible.

Ch. 5: The Head

Interesting Fact — Researchers who study decapitations have found that “a decapitated head will still have some oxygen in it, so loss of consciousness may not be instantaneous.” 😳
Facial Recognition — Interestingly, more than 40 muscles, a significant portion of the body’s total, are involved in facial expression. Whole regions of the brain are devoted solely to recognizing faces and expressions. We are also extremely sensitive to the slightest alteration of mood or expression. We just tend to pick up on facial expressions really well, even if we aren’t always fully conscious of them.
Facial Features & Senses — The real purpose of most of our facial features is to help us interpret the world through our senses. The head has three familiar senses worth noting: sight, hearing, and smell.
Senses: Sight — About a third of your entire cerebral cortex in the brain is engaged with vision. Interestingly, the eye is built back to front — the rods and cones that detect light are at the rear, but the blood vessels that keep it oxygenated are at the front. Interestingly, we have ‘blind spots’ in our field of vision and “a significant part of what we see is actually imagined” by the brain. There are several interesting phenomena involved with sight:
- Floaters — The brain normally edits out any interferences, but it doesn’t always succeed. This is experienced when seeing “floaters and “white sparks” while looking at a clear blue sky. These are really your own white blood cells moving in front of the retina.
- Tears — We produce about 5-10 ounces of tears every day. The tears drain away through holes in the corner of each eye beside the nose. When we cry emotionally, these areas can’t drain the fluid fast enough, so it overflows our eyes and runs down our cheeks. We also have three types of tears: basal, reflex, and emotional.
Senses: Hearing — Like sight, hearing is a miracle. We hear extremely well, much better than would be expected based on how the ear is designed. Our pain threshold for noise is about 120 decibels, and noises above 150 decibels can burst the eardrum. A library or countryside has about 30 decibels of noise. Other things to note about hearing include:
- Balance — The ear is also very involved in balance via the vestibular system, as I have learned from personal experience. There’s a gel inside our head that moves/shifts and tells the brain which direction we are traveling. When we feel dizzy, it’s because the gel keeps moving even though the head has stopped moving. The gel thickens as we age and doesn’t slosh around as well, which is one reason why elderly people are not steady on their feet. When loss of balance happens for a long period of time, the brain interprets it as poisoning, which is why loss of balance (i.e. vertigo) often results in nausea.
- The Valsalva Effect — The Valsalva effect arises when air pressure inside you head fails to keep up with the changing air pressure outside of it. You experience the Valsalva effect when changing heights rapidly, as often happens in an airplane. Keeping your noise plugged and blowing out through the ears is known as the Valsalva maneuver.
Senses: Smell — The science of smell is very interesting in that nobody really smells things the same. We all have 350-400 types of odor receptors, but only half of them are common in all people. That means what Johnny is smelling when presented with a certain odor might be different than what I’m smelling. We also know very little about odors and smell because there aren’t many people focused on researching it. There are usually many different chemicals that go into a single smell and none of the individual chemicals typically smell like the final outcome.
Chapter Takeaway — The head is where our senses live. Eyesight, hearing, and taste are senses that we often take for granted but bring a lot of vitality to our lives. The way the eyes and brain work together to project our world is complex but very interesting.

Ch. 6: Down the Hatch - The Mouth and Throat

Swallowing — We swallow about 2,000 times per day; once every 30 seconds or so. When you swallow, food doesn’t just drop into your stomach by means of gravity — it is pushed down by muscular contractions in the throat and other areas of the mouth. Altogether, 50 muscles are involved in getting a piece of food to your stomach, and they must sync up perfectly and work together to avoid choking.
- Quote (P. 95): “Uniquely among mammals, we send our air and food down the same tunnel. Only a small structure called the epiglottis, a kind of trapdoor for the throat, stands between us and catastrophe. The epiglottis opens when we breathe and closes when we swallow, sending food in one direction and air in another, but occasionally it errs and the results are sometimes dire… It is pretty amazing when you reflect upon it that you can sit at a dinner party enjoying yourself extravagantly — eating, talking, laughing, breathing, slurping wine — and that your nasopharyngeal guardians will send everything to the right place, in two directions, without you having to give it a moment’s consideration. That’s quite an accomplishment.”
The Heimlich Maneuver — Considering the precision required and the number of times in a lifetime that the systems are challenged by eating, it’s amazing that we don’t choke more often. The most well-known solution to a choking crisis is the Heimlich maneuver, named for Dr. Henry Judah Heimlich, a surgeon from New York who invented it. The maneuver involves embracing a chocking victim from behind and giving him/her a series of sharp hugs at the breastbone to force out the blockage, like a cork from a bottle.
Saliva — The mouth is a moist and glistening area because there are 12 salivary glands in and around it. That’s one of the reasons so many microbes and bacteria call the mouth home — you have about 200 species of bacteria in your mouth at one time. Saliva is 99.5% water, but the other 0.5% is full of useful enzymes. Interestingly, we don’t produce saliva at night while we’re asleep. That’s why our mouth is dry in the morning. It’s also why microbes and bad-smelling chemicals pile up overnight and make our breath stink in the morning.
Interesting Fact — The outside of your tooth is called the enamel. It is the hardest substance in the human body, but forms just a thin layer and can’t be replaced if it is damaged.
The Tongue & Taste Buds — The tongue is a muscle unlike any other. It is extremely sensitive, which is how you pick out things in your food that shouldn’t be there (i.e. eggshell) and react to hold and cold so sharply. The tongue is coated with taste buds, which are taste receptor cells found in the bumps on your tongue. They are the most regenerative cells in the body and are replaced every ten days. We have about 10,000 of them, and they are everywhere on the tongue except the very middle.
Interesting Fact — Puffer fish contain a poison called tetrodotoxin, which is 1,000 times more powerful than cyanide. You don’t want to eat these. But despite its extreme toxicity, puffer fish is a famous delicacy in Japan, where it is called fugu. Preparing fugu is a job entrusted to only a few specially trained chefs, who must carefully remove the fish’s liver, intestines, and skin before cooking because they are particularly saturated in poison. Even then, enough toxin remains to numb the mouth and leave the dinner feeling pleasantly woozy. On average, one person per year dies from overeating puffer fish.
Capsaicin: The Spicy Stuff! — The primary active ingredient in chilis and many other spicy things is capsaicin. They’re even in Hot Cheetos! Capsaicin in its pure form has 16 million Scovilles. Capsaicin has been reported to lower blood pressure, fight inflammation, and reduce susceptibility to cancer, among many benefits. Capsaicin grew in peppers as a self-defense mechanism after small mammals kept eating peppers.
Scoville Rating — We actually have more pain receptors in our mouth than taste buds. These pain receptors give us feedback when we’ve eaten spicy things like chilis, which have capsaicin as the primary active ingredient. The amount of heat in chilies is measured in units called Scovilles, after Wilbur Scoville (1865-1942), an American pharmacist. A bell pepper has a rating of between 50 and 100. Jalapeños come in at 2,500-5,000 Scovilles. The system is also used to measure other spicy things — Hot Cheetos range from 50-50,000 Scovilles.
Chapter Takeaway — We have a ton of taste buds, and even more pain receptors, in our mouth. The Scoville rating is a measure of how spicy something is. Don’t eat puffer fish.

Ch. 7: The Heart and Blood

The Heart — The heart has one job, and it does it extremely well: it beats. It beats around 100,000 times per day, rhythmically pushing blood through and around your body. Every hour, your heart dispenses around 70 billion gallons of blood — that’s 1,680 gallons in a day, more gallons pushed through you in a day than you likely put into your car in a year. The heart pumps blood with enough force to send it to your outermost extremities and back; not an easy task.
The Heart: Size & Chambers — The heart weighs less than a pound and is divided into four simple chambers: two atria and two ventricles. Blood enters through the atria (think entry room) and exits via the ventricles. 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, but actually the greatest amount, 20 percent, goes to the kidneys. The journey of blood around your body takes about 50 seconds to complete.
Interesting Fact — The heart looks nothing like the popular heart shape we all know ❤️. The symbol of a red heart first appeared in paintings from Northern Italy in the early 1300s, but nobody really knows what inspired it.
Heartbeat & Blood Pressure — The two phases of a heartbeat are known systole (when the heart contracts and pushes blood out into the body) and diastole (when it relaxes and refills). The difference between the two is your blood pressure. The two numbers in a blood pressure reading (e.g. 120/80) measure the highest and lowest pressures your blood vessels experience with each heartbeat. The first number is the systolic pressure; the second is the diastolic. Blood pressure isn’t a fixed figure — it changes from one part of the body to another and across the body as a whole throughout the day. One of the reasons it’s important to get up and move around regularly is that by contracting your muscles, especially in the legs, you are helping blood get back to the heart. The American Heart Association says 130/80 and above is hypertension.
Heart Disease — Heart disease is the leading cause of death. There are many issues that can happen with the heart. Two of the most common include:
- Heart Attack — Occurs when oxygenated blood can’t get to the heart muscle because of a blockage in a coronary artery. When the heart is deprived of oxygen, it begins to die. Heart attacks are sudden, whereas some other forms of heart failure are often more gradual.
- Cardiac Arrest — Occurs when the heart stops pumping altogether, usually due to failure in electrical signaling. When the heart stops pumping, the brain is deprived of oxygen and you become unconscious and die, unless you get immediate treatment. A heart attack often leads to cardiac arrest, but you can suffer cardiac arrest without having a heart attack.
Blood — Blood carries oxygen to our cells. But it also does a lot more — it transports hormones and chemicals, carries off waste, tracks down and kills pathogens, ensures oxygen is directed to the areas of the body where it is most needed, regulates body temperature, helps with male elections. A single drop of blood may contain 4,000 different types of molecules. That’s why doctors are so focused on blood tests; blood is packed with information. There are four main layers of blood:
- Plasma — Plasma is the most abundant layer in the blood, making up over half of the blood’s volume. It is 90% water.
- Red Blood Cells — These are the next most plentiful component constituting about 14 percent of the total volume of the blood. Red blood cells are designed to do one job: deliver oxygen to our other cells throughout the body. They are very small but very abundant. A teaspoon of human blood contains about 25 billion red blood cells. Red blood cells are almost entirely hemoglobin, which is the most important part of a red blood cell. Hemoglobin is a protein in red blood cells that carries oxygen; it’s basically a shipping container for the oxygen. A typical red blood cell will be shot around the body about 150,000 times before it is too battered to go on. AT that point, the battered cell will be collected and sent to the spleen to be discarded. You discard about 100 billion red blood cells every day. These discarded red blood cells are a big reason your poop is brown and your urine is yellow.
- White Blood Cells — White blood cells are critical for fighting off infections. Your immune system uses them to help fight infections of all kinds. You have over 700 times as many red blood cells as white ones.
- Platelets — Platelets are the final part of the blood and account for less than 1% of the blood’s volume. They play a huge role in blood clotting. Clotting is designed to stop bleeding. As soon as a bleed starts, millions of platelets begin to cluster around the wound and deposit material called fibrin. Together, these form a plug to stop the bleeding. If the bleeding is too much, platelets can’t stop it. That’s why major bleeds have to be stopped by putting a lot of pressure on the wound via a towel or something like that.
History of Bleeding — Prior to 1885 or so, bleeding was actually thought to help fight infections and other ailments. Many people resorted to intentional bleeding to try to fight an illness. After George Washington developed a bad sore throat in 1799, his doctors decided to bleed him 4 times. Over 40% of his blood was removed over two days. He died shortly after. Bleeding bowls were actually treasured within families and passed on as heirlooms.
Blood Types — The way blood typing works is this: All blood cells are the same inside, but the outsides are covered with different kinds of antigens — proteins that project outward from the cell surface — and that is what accounts for blood types. This is similar to apo-A and apo-B and their role with cholesterol on the blood. The four main antigens that cover the blood cells, and which make up the four blood types, are:
- Type A
- Type B
- Type AB
- Type 0
How Blood Types Work — People with blood type A can donate to those with A or AB but not B; people with B can donate to B or AB but not A; people with AB can donate only to other people with AB blood. People with type O blood can donate to all others, and are known as universal donors. Type A cells have A antigen on their surface, type B have B, and type AB have both A and B. Put A type blood in a B type person and the recipient body sees it as an invasion and attacks the new blood.
Blood Transfusions — One of the big reasons blood transfusions don’t always work out is that blood is a living thing, just like the heart or liver. When it is extracted from people (via a blood donation, for example), it immediately starts to degrade. The FDA says blood can be kept for transfusion for a max of 42 days, similar to how long a typical blood cell circulates in the body. That said, the longer it sits in storage, the less effective it is if given to another person with the same blood type. Blood banks normally dispatch their oldest blood first to beep their stock fresh so almost everybody gets old blood when receiving a transfusion. Different blood in the body also has a tendency to cause confusion and complications. All of this has led to doctors to avoid blood transfusions if possible.
Nitric Oxide & Blood Distribution — Nitric oxide is responsible for directing blood to the areas of the body that need it most based on every moment in every day. Most people think that blood is equally distributed in the body, but it’s not. If you are sitting down, for example, your legs won’t need as much blood because the tissues there won’t need as much oxygen. But if you get up and start running, your legs will need more oxygen, and nitric oxide will purposely direct more blood to them as a result.
Chapter Takeaway — The heart pumps blood to all areas of the body. Blood carries oxygen to all of our cells to keep them up and running.

Ch. 8: The Chemistry Department

Discovery of Insulin — Insulin is a small protein/hormone released by the pancreas that is vital to maintaining balance of blood sugar in the body. Insulin was discovered in the late 1800s and is considered one of the great medical findings of all time because diabetes was a quick death sentence in those days. After insulin was discovered, doctors found ways to produce large quantities of it to give to patients. Insulin allowed those with diabetes to bring down their elevated blood sugar levels right away, which saved their lives.
Diabetes — Diabetes comes in two forms. Both essentially come from chronically high blood sugar levels in the body. Diabetes is a growing problem — between 1980 and 2014, the number of adults with diabetes went from 100 million to over 400 million. The two types of diabetes are:
- Type 1 Diabetes — With Type 1 diabetes, the body just stops producing insulin altogether. Insulin is the protein and hormone released by the pancreas to help get rid of excess sugar in the bloodstream.
- Type 2 Diabetes — With Type 2 diabetes, insulin is less effective in the body. This either means (a) the pancreas isn’t producing enough insulin to dispatch the excess sugar in the bloodstream or (b) the cells in your muscles, fat, and liver are insulin resistant, meaning they don’t accept the insulin your body is producing, so your blood sugar levels stay elevated.
Endocrine Gland vs. Exocrine Gland — An endocrine gland is one that secretes its products directly into the bloodstream, while exocrine glands secret onto a surface (e.g. sweat glands onto skin or salivary glands into the mouth). The key endocrine glands are the thyroid, pancreas, pituitary, testes, and ovaries.
Pituitary & Endorphins — The pituitary is often called the master gland because it controls so much. It produces or regulates growth hormone, cortisol, estrogen, testosterone, oxytocin, adrenaline, and more. Endorphins are the body’s natural painkillers. Endorphins are released by the hypothalamus and pituitary gland in response to pain or stress, this group of peptide hormones both relives pain and creates a general feeling of well-being. 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,
Hormones — Hormones are chemicals that coordinate different functions in your body by carrying messages through your blood to your organs, skin, muscles and other tissues. These signals tell your body what to do and when to do it. There are over 50 known hormones and they are incredibly complicated molecules. Every hormone is very flexible in that it can handle many different responsibilities. A few of the known hormones include:
- Cortisol — Cortisol is a stress hormone that regulates blood pressure and overall stress in the body. It is produced and released by the adrenal glands.
- Oxytocin — Oxytocin is a hormone well known for its role in generating feelings of attachment and affection. It is sometimes called the “hug hormone.”
- Testosterone — Testosterone is found in men and women. In men, it makes a man fertile, gives him attributes like a deep voice and facial hair, and influences behavior via sex drive and a taste for risk and aggression. It is primarily produced in the testes. Testosterone levels tend to fall by 1% a year beginning in the 40s.
The Liver — A gland is any organ in the body that secretes chemicals. Compared to our other glands, the liver is huge. It weighs three pounds and is located in the central abdomen just below the diaphragm. It is the most busy organ in the body and has responsibilities so vital to our health that we would be dead in a few hours if it shut down. What’s maybe most remarkable about the liver is that it can regenerate. You could remove 2/3 of your liver and it will grow back to its original size in a matter of weeks.
- Functions — Among its many jobs, the liver manufactures hormones, proteins, and the digestive juice known as bile. It filters toxins, disposes of old and battered red blood cells, stores and absorbs vitamins, converts fats and proteins to carbohydrates, and manages glucose levels in the bloodstream — a process which is so vital for the body that its absence for even a few minutes can cause organ failure and even brain damage. More 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 bodys laboratory. Right now, about a quarter of all your blood is in your liver.
The Pancreas — The pancreas is packed in beside the liver behind the stomach and in the upper abdomen area. Like the liver, the pancreas is a gland that secretes chemicals inside the body. The pancreas is a jellylike organ, about six inches long, shaped roughly like a banana (and about the same size). As well as insulin, it produces the hormone glucagon, which is also involved in regulating blood sugar, and the digestive enzymes trypsin, lipase, and amylase, which help digest cholesterol and fats. Altogether every day it produces over a quart of pancreatic juice.
The Spleen — The spleen is roughly the size of your fist, weighs half a pound, and sits fairly high up on the left side of your chest. It does important work monitoring the condition of circulating blood cells and dispatching white blood cells to fight infections. It also acts as a reservoir for blood so that more can be supplied to muscles when suddenly needed. It also aids the immune system.
The Kidneys — You have two kidneys. The kidneys are called the workhorses of the body. Each day they process about 190 quarts of water — that is the amount a bath holds up to the overflow level — and 3.3 pounds of salt. They are located at the bottom of the rib cage.
- Function — Filtering wastes is the principal function of the kidneys, 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 over too long a period, they get tired and stop functioning well. As the kidneys become less efficient the sodium levels in your blood creep up, pushing your blood pressure dangerously high. More than most other organs, the kidneys lose function as you age. Between the ages of forty and seventy, their filtration capacity drops by about 50 percent.
The Urinary Bladder — What the kidneys don’t return to the body via the bloodstream, they pass on to the urinary bladder for disposal. Each kidney is connected to the bladder via a run called a ureter. The urinary bladder is like a balloon in that it is designed to swell as we fill it (with fluid, aka pee). As we age, the bladder loses elasticity and can’t expand as much as before, which is partly why old people have to go to the bathroom so much.

Ch. 9: In the Dissecting Room - The Skeleton

Gray’s Anatomy — In 1858, Henry Gray and Henry Vandyke Carter published Anatomy: Descriptive and Surgical, which later became known as Gray’s Anatomy. The book was the first extensive breakdown of the human body from an anatomy perspective. The book is very long and outlines the different roles and functions of the body and its components.
Bones — Our skeleton is truly amazing and allows us to do so many different things with relative ease. We have about 206 bones, but the number depends on the person. We have 52 bones in our feet alone, and the hands and feet together have more than half of the bones in the body. Because of the way they are constructed, bones are both extremely strong and light. Altogether, your bones weight about 20 pounds, but they can handle a huge amount of compression. Maybe most remarkably, bone can grow back.
Collagen — Typically about 70% of a bone is inorganic material and 30% organic. The most fundamental element of a bone is collagen, which is the most abundant protein in the body with 40% of our proteins being collagen.
- Quote (P. 166): “Collagen makes the white of the eye but also the transparent cornea. In muscle it forms fibers that behave just like rope in that they are strong when stretched but collapse when pushed together. That’s great for muscle but wouldn’t be so useful in your teeth. So when permanent stiffness is needed, collagen often twins with a mineral called hydroxyapatite, which is strong when compressed and thus allows the body to create good solid structures like bones and teeth.”
Tendons & Ligaments — 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 extensions of muscles. Tendons are strong, and generally it takes a lot of force to tear them, but they also have very little blood supply and therefore take a long time to heal.
Muscle — We have more than 600 muscles altogether, and our body is about 40% muscle. We tend to notice our muscles only when they ache, but they are involved in so many things that we don’t even think about, like puckering our lips, blinking our eyelids, moving food through the digestive tract. It takes 100 muscles just to stand up. You need 12 to move your eyes when reading. When resting, it takes 40% of your energy allowance just to maintain the muscle in your body (and much more when you’re active). Because muscle takes up so much energy to maintain, we lose it quickly when we aren’t using it. Studies by NASA have shown that astronauts can lose up to 20% of muscle mass (and bone density) on short missions.
Thumbs — Our thumbs are really what help us stand apart from any other animal on earth. We have three muscles inside our thumbs — the extensor pollicis brevis, the flexor pollicis longus, and the first volar interosseous of Henle — that allow us to grasp and manipulate tools with sureness and delicacy. The thumbs are really an under-appreciated part of our body.
- Quote (P. 169): “You might never have heard of them, but these three small muscles are at the heart of human civilization. Take them away and our greatest collective achievement might be maneuvering ants out of their nests with sticks.”
Back and Lower Body Problems — One of the main reasons back problems are so common is that we didn’t use to walk on two feet. We evolved over time to the point of walking on two limbs rather than all four. With those changes (which took place over millions of years), we have adopted back pain because of the redistribution of our weight load. Our hips and knees have also taken a hit from that evolutionary change via wear and tear on the cartilage lining the joints. Hips often give out because they have to do two tough things: provide mobility for the lower limbs and support the weight of the body. The hip socket and head of the femur end up grinding on each other over time, which causes pain and discomfort. That’s why hip surgeries are fairly common.
Bone Density Loss — We lose bone mass at a rate of about 1% per year from late middle age onward, which is why elderly people break bones so easily. Broken hips are especially tough on older people. About 40% of people over 75 who break their hip are no longer able to care for themselves. For many it’s the last straw — 10% die within 30 days and nearly 30% did within 12 months. This is why it’s so important to build your body up to avoid and/or withstand falls in old age. Falls and injuries in old age are so damaging because they lead to bone loss and inactivity while recovering. For many, a fall or major injury in old age sends them into a rapid tailspin.

Ch. 10: On the Move - Bipedalism and Exercise

Bipedalism — Out of over 250 species of primates, humans are the only ones to get up and move around on two legs. Bipedalism is about as defining of a characteristic of what it means to be human as our high-functioning brain. We evolved to bipedalism — our ancestors used to be completely hairy and climb/live in trees. The protohuman famously known as Lucy lived in what is now Ethiopia some 3.2 million years ago. She is often used as a model for early bipedalism. She weighed 60 pounds and was 3.5 feet tall.
- Quote (P. 174): “Many theories have been proposed as to why our distant ancestors dropped out of trees and adopted an upright posture — to free their hands to carry babies and other objects; to gain a better line of sight across open ground; to be better able to throw projectiles — but the one certainty is that walking on two legs came at a price. Moving about in the open made our ancient forebears exceedingly vulnerable, for they were not formidable creatures, to say the least.”
Anatomy Changes — After becoming bipedal, we developed a set of important anatomical changes over the course of 6 million years or so to support our new structure. We shed most of our hair to allow for sweat glands to release sweat and cool our bodies as we run and exercise. Our head and facial setup changed. We developed a gluteus maximus (butt) and achilles tendon to power our bodies forward. The nuchal ligament in the back of our head was developed to hold the head steady when running.
Running & Throwing — We run better than any other species. We aren’t the fastest, but because we have very little hair and we have sweat glands that allow us to perspire and therefore cool the body, we can run longer distances than any other animal. All other mammals lose heat by respiration (panting). If they can’t stop to collect themselves, they will overheat and become helpless. Most large animals can’t run more than 9 miles. Also during this time, we developed the ability to throw things. All of these developments allowed us to hunt very well.
Exercise — As discussed in other books (especially Outlive by Peter Attia), exercise is vital to our health and wellness, mentally, physically, and emotionally. The evidence and benefits of exercise cannot be disputed. A consistent exercise routine is one of the single best things you can do for yourself and your body. Just going for regular walks reduces your chances of a heart attack or stroke by 31%.
- Quote (P. 179): “As well as strengthening bones, exercise boosts your immune system, nurtures hormones, lessens the risk of getting diabetes and a number of cancers (including breast and colorectal), improves mood, and even staves off senility. As has been noted many times, there is probably not a single organ or system in the body that does not benefit from exercise. If someone invented a pill that could do for us all that a moderate amount of exercise achieves, it would instantly become the most successful drug in history.”
  - Takeaway — As Peter Attia pointed out in Outlive, exercise is more powerful than medicine. It’s the single best thing you can do for your health.
Move! — Get out and move as much as you can. Sitting on the couch (or a workstation) for long periods of time over years is very bad for you. According to one study, people who sit for 6 hours or more per day have a 20% greater chance of mortality than those who don’t sit around for that amount of time consistently. These same people also have considerably higher chances of having a heart attack or stroke. Whenever possible, get up and just walk around for a bit.
Interesting Fact — Our ancestors had to survive times where food was readily available and times when it was very hard to find. To survive the lean times, we developed the ability to store fat on our body for the purpose of having it readily available for fuel if needed. The problem is that we now live in a time where food is very easy to get 24/7. Many people eat way too much, resulting in more fat stored on the body as fuel, resulting in obesity. This wasn’t a problem for our ancestors, who didn’t have access to bad food 24/7.
Interesting Fact — We burn a good amount of calories just existing. The heart, brain, and kidneys burn about 400 calories a day each, the liver about 200. The process of eating and digesting food alone accounts for about one-tenth of the body’s daily energy requirements. But we can do much more by simply getting up off our backsides. Even just standing burns an extra 107 calories an hour. Walking around burns 180. In one study, volunteers were instructed to watch television as normal through an evening, but to get up and walk around the room during every commercial break. That alone burned 65 extra calories an hour, about 240 calories over an evening.
Chapter Takeaway — Exercise! Move your body! Exercise is the single best thing you can do for your body and your mental, physical, and emotional health.

Ch. 11: Equilibrium

Body Temperature — Our body temperature varies throughout the day, but normally doesn’t stray too far away from 98.6 degrees Fahrenheit. Straying away from that number becomes dangerous. A fall of just two degrees below normal, or a rise of four degrees above, can tip the brain into crisis that can lead to big damage or death. A fever is a slight rise in body temperature, and usually signals that your body is busy fighting something off.
Cellular Energy — The body requires a staggering amount of energy at the cellular level to maintain itself. In fact, the amount of electricity going on within your cells is a thousand times greater than the electricity in your house.
ATP — The stuff responsible for the energy in our cells is a chemical called adenosine triphosphate (ATP). Every molecule of ATP is like a tiny battery in that it stores up energy and releases it to power all the activities required by your cells. The chemistry involved in the process is very complex. It’s enough to know that we are very dependent on ATP to keep our cells running well. ATP is produced in the body and then consumed almost immediately, which means we have only about 60 grams of it inside of us at any given moment.
Body Size & Gravity — Body size has a great deal to do with how we are affected by gravity. A small bug that falls off a tabletop will land unharmed and continue on its way unperturbed. That is because its small size (strictly, its surface area-to-volume ratio) means that it is not really affected by gravity. The bigger you are, the more you feel the punishment of a fall.

Ch. 12: The Immune System

The Immune System — Any invader that gets past our outer defenses (skin, earwax, tears, etc.) will run into swarms of immune cells (like T cells), which come pouring out of lymph nodes, bone marrow, the spleen, the thymus, and other corners of the body. Our immune system is in place to defend us from viruses, germs, drugs, toxins, cancers, foreign objects, and anything else that it doesn’t recognize.
- Quote (P. 201): “Despite the intricacy at the molecular level, all parts of the immune system contribute to a single task: to identify anything that is in the body that shouldn’t be there and, if necessary, kill it.”
Stress — Stress has a big impact on our immune system. When we we are stressed or exhausted, we are more likely to suffer an infection of some sort. Because protecting us from invasion is such a limitless challenge, the immune system sometimes makes mistakes and launches an attack on innocent cells.
White Blood Cells / Lymphocytes — At the heart of our immune system are five types of white blood cells: lymphocytes, monocytes, basophils, neutrophils, and eosinophils. They are all important, but lymphocytes are maybe the most important. They are known as some of the cleverest cells in the body because of their ability to recognize almost any unwanted invader and lead a swift and targeted response. Lymphocytes come in two types:
- B Cells — B cells are made in the bone marrow. Their primary function is to make antibodies. These are important when we’re fighting off a pathogen.
- T Cells — T cells are made in the thymus, a small organ in the chest just above the heart and between the lungs. T cells are like elite assassins that go out and kill bad cells. They are subdivided into three categories:
  - Helper T Cells — These T cells help other immune cells act. For example, they help B cells make proteins called antibodies.
  - Killer T Cells — These T cells kill cells that have been invaded by pathogens.
  - Memory T Cells — These T cells remember the details of earlier invaders and are therefore able to coordinate a quick response if the same infection or pathogen shows up again. Memory T cells instruct B cells to produce antibodies and tell them to attack the invading pathogen. This process is known as adaptive immunity. This process is also why you often only get one particular sickness once in your life. It’s also the process at the heart of vaccination.
Cancer — In addition to killing invasive cells, the immune system must also kill our own cells when they misbehave and become a problem, as is the case when they turn cancerous.
Inflammation & Fever — 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.
- Quote (P. 203): “Unlike red blood cells, white blood cells can leave the circulatory system to pass through surrounding tissues, like an army patrol searching through jungle. When they encounter an invader, they fire off Unlike red blood cells, white blood cells can leave the circulatory system to pass through surrounding tissues, like an army patrol searching through jungle. 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.”
Chapter Takeaway — When you feel sick or have a fever, what you’re really feeling is the rigors of your body defending itself from a pathogen of some kind. Your body is mounting an attack on the invading cells, which causes you to feel unwell. The immune system is all about defending your body.

Ch. 13: Deep Breath - The Lungs and Breathing

The Lungs and Diaphragm — Altogether the lungs weigh about 2.4 pounds, and they take up more space in your chest than you probably realize. They jut up as high as your neck and bottom out at about the breastbone. We tend to think of them as inflating and deflating independently, like bellows, but in fact they are greatly assisted by one of the least appreciated muscles in the body: the diaphragm. By pulling down on the lungs from below, the diaphragm helps the lungs to work more powerfully. The increased respiratory efficiency that the diaphragm brings enables us to get more oxygen to our muscles, which helped us to become strong, and to our brains, which helped us become smart.
CO2 and Oxygen — Interestingly, the discomfort you feel when you hold your breath for too long is caused not by the depletion of oxygen but by a buildup of carbon dioxide. That’s why the first thing you do when you stop holding your breath is blow out. You would think that the most urgent need would be to get fresh air in rather than stale air out, but no. The body so abhors CO2, that you must expel it before gulping in replenishment.
Bad Breathers — We are inefficient breathers. Our lungs can hold about six quarts of air, but normally we breathe in about half a quart at a time. There’s a lot of room for improvement with our breathing. It takes some work, but proper breathing is a lifechanger.

Ch. 14: Food, Glorious Food

Calories & Body Weight — The calorie is basically 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. Just how many calories each of us needs is pretty much a personal matter. In the end, you will put on weight if you consistently eat more calories than what your body requires in a day. You will lose weight if you consistently eat fewer calories than what your body requires in a day. It doesn’t matter what you eat from a calorie and body weight standpoint. When it comes to your overall health, what you eat does matter.
Vitamins & Minerals — Protein, carbs, and fat are the three macronutrients of a diet. For most people, it’s pretty much impossible to get all of the vitamins and minerals you need from diet alone. That’s where supplements come in. Supplements can help you get the necessary amount of vitamins and minerals on a consistent basis. Altogether, there are about 40 vitamins and minerals that we must get from our diet or supplements because we can’t produce them for ourselves in the body. Interestingly, the risk of getting too many vitamins and minerals is as great as the risk of getting too little; it’s easy to get too many, which causes problems just like not getting enough causes issues.
- Vitamins — Vitamins are organic chemicals from things that are or were once alive, like plants and animals.
- Minerals — Minerals are inorganic and come from soil or water.
- Quote (P. 233): “According to the Centers for Disease Control, far from having plenty in our diet, some 90% of American adults don’t get the recommended daily dose of vitamins D and E and about half don’t get sufficient vitamin A. No less than 97%, according to the CDC, don’t get enough potassium, a vital electrolyte, which is particularly alarming because potassium helps to keep your heart beating smoothly and your blood pressure within tolerable limits.”
  - Takeaway — Eat your bananas! It’s important to get potassium in your diet.
Interesting Fact — Contrary to popular belief, Vitamin C does not help you get rid of a cold. This is a myth that dates back to the mid-1900s, when Linus Pauling made the case that large doses of Vitamin C helped keep his prostate cancer at bay. His claims have since been discredited.
Proteins — In simple terms, a protein is a chain of amino acids. There are a million different proteins, but they are all made using just 20 amino acids, even though hundreds of amino acids exist. Overall, 8 of the 20 amino acids cannot be made in the body and must be consumed in the diet. A small number of amino acids in a chain make a peptide. Ten or twelve strung together makes a polypeptide. When a polypeptide gets bigger than that, it becomes a protein. Protein from meat is more effective than protein from plants because they contain more/better amino acids.
Carbohydrates — Carbs are compounds made 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. 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.
- Quote (P. 235): “The main thing to bear in mind is that carbohydrates, upon being digested, are just more sugar — often quite a lot more. That means that 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.”
  - Takeaway — Carbs of any variety (bread, Gatorade, sugar, etc.) all have the same effect on your blood glucose levels. They will all drive blood glucose levels up because they contain glucose.
Fats — Carbohydrates and fats are the two main fuel reserves of the body, but they are stored and used in different ways. When the body needs fuel it tends to burn up the available carbohydrates and store any spare fat. The main point to bear in mind is that the human body likes to hold on to its fat. It burns some of the fat we consume for energy, but a good deal of the rest is stored on the body as fat. Depending on where it ends up, fat is known as subcutaneous (beneath the skin) or visceral (around the belly). As also described in Outlive, visceral fat is much worse than subcutaneous.
Interesting Fact — In June 2004, the United States Department of Agriculture (USDA) classified french fries as a vegetable!
Salt — Salt is actually vital to us. We would die without it. In fact, lack of salt is nearly as dangerous to us as lack of water. Our bodies can’t produce salt, so we have to consume it in our diets. The key is to determine how much is the right amount. Too little leads to low sodium levels, which can be very dangerous. Too much can contribute to high blood pressure and potentially heart disease or stroke.
Chapter Takeaway — It’s important to eat healthy, but it doesn’t guarantee you a longer life. It definitely improves your probability of living a longer, healthier life, but it doesn’t guarantee it by any means. Carbs of any kind elevate your blood glucose levels. Stay away from sugar as much as humanly possible. Eat a lot of fiber because it’s good for your gut health. Salt, surprisingly, is really important to our overall health.

Ch. 15: The Guts

The Stomach — Contrary to popular belief, the stomach is not located in the belly area; it’s located much higher up and is off on the left side of your body. The stomach is less vital than most people think. It contributes a bit to digestion both chemically and physically, by squeezing its contents with muscular contractions and bathing them in hydrochloric acid, but its contributions to digestion are more helpful than vital. The real digestion and absorption happens further down. Maybe the best thing the stomach does is soak bacteria from food we eat in hydrochloric acid. Without the stomach doing that, a lot more of what we eat would make us sick.
Digestive Process — Roughly speaking, each meal you eat spends about 4-6 hours in the stomach, a further 6-8 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 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. That’s why we are told to eat a lot of fiber: it keeps our gut microbes happy and also reduces the risk of heart disease, diabetes, and death of all types.
Interesting Fact — The “rumblings” from your stomach signaling that you’re hungry don’t come from the stomach — they come from the large intestine.
Foodborne Illness — Foodborne illness is America’s secret epidemic. Every year 3,000 people died of food poisoning in the U.S. E. coli and salmonella are two of the worst, but there are many.
Food Safety — Altogether there are 15 agencies that have some kind of regulatory role over American food safety. There is no one agency that has overall control. For example, there is an agency (FDA) that looks at the skin on sausages, but another agency is responsible for the contents inside the sausage. There is an agency that looks at frozen cheese pizza while another agency looks at meat pizzas.
Jack in the Box E. coli Outbreak — In 1992, Jack in the Box had an E. coli outbreak that killed a 6-year-old and caused illness to over 700 other customers, some of whom suffered organ failure. The outbreak occurred because the fast food restaurant failed to cook their hamburgers to the recommended temperature because they felt the burgers at that temperature were “too tough.”
Small Intestine & Large Intestine — The heart of the digestive process is the small intestine, 25 feet of coiled tubing where most of the body’s digestion takes place. Wrapped around the outside of the small intestine is the large intestine/bowel/colon. The large intestine is engaged in a lot of important work. It reabsorbs large volumes of water, which it returns to the body. It also provides a warm home for vast colonies of microbes that chew away at whatever the smaller intestine hasn’t taken already, in the process capturing lots of useful vitamins like B, B2, B3, B4, and K, which are also returned to the body. What’s left is dispatched for evacuation as feces.
The Appendix — The appendix serves as a reservoir for gut bacteria. It isn’t really needed, but 1 in 16 in the developed world will suffer from appendicitis at some point, enough to make it the most common cause of emergency surgery. Without surgery, many appendicitis victims would die.
Farts — Farts consist primarily of carbon dioxide (up to 50%), hydrogen (up to 40%) and nitrogen (up to 20%). The smell of a fart is largely hydrogen sulfide, even though hydrogen sulfide is a very small part of what is expelled. Interestingly, farts can be explosive is they contain hydrogen and methane.

Ch. 16: Sleep

Sleep Benefits — Sleep has been tied to many great biological processes — consolidating memories, restoring hormonal balance, emptying the brain of accumulated neurotoxins, resetting the immune system. People with early signs of hypertension who slept for one hour more per night than previously showed a significant improvement in their blood pressure readings. It seems to be a kind of nightly tune-up for the body.
The Sleep Cycle & REM Sleep — A normal night of sleep consists of a series of cycles involving 4-5 phases that takes the sleeper through various light-medium-deep stages of sleep. The cycle repeats 4-5 times a night and takes about 90 minutes to complete. The final stage of a typical cycle is the Rapid Eye Movement (REM) stage, the most interesting and mysterious of the stages. This is where we do our dreaming. During REM, the sleeper becomes mostly paralyzed, but the eyes dart about beneath closed lids and the brain grows as lively as at any time during wakefulness. Not all of you is paralyzed during the REM phase. Your heart and lungs continue to function, but the muscles that control bodily movement are all restrained. This is why you sometimes wake up and can’t move for a brief few seconds.
Sleep Drive & Adenosine — There’s only so long you can stay awake before your body “forces” you to sleep. We all have a sleep drive. The pressure to sleep grows stronger the longer we stay awake. This is in large part a consequence of an accumulation of chemicals in the brain as the day goes by, in particular one called adenosine, which is a by-product of the output of ATP (or adenosine triphosphate), the little molecule of intense energy that powers our cells. The more adenosine you accumulate, the drowsier you feel. Caffeine doesn’t provide energy; rather it temporarily “blocks” adenosine from reaching its receptors in the brain, thereby negating its sleep effects for a brief time. The adenosine then builds up and hits you all at once, which is the “caffeine crash” that a lot of people describe.
Chapter Takeaway — There is no part of your mind or body that doesn’t benefit from sleep. It is critical for your overall health and well-being. Getting good, consistent sleep is a game-changer. Its acts almost like a nightly tune-up. From an evolutionary standpoint, it’s not fully understood why we sleep.

Ch. 17: Into the Nether Regions

X and Y Chromosomes — Females have two X chromosomes and males have one X and one Y chromosome, which accounts for their sexual differences.
- X Chromosome — A zoologist named Hermann Henking discovered the X chromosome in 1891 while studying the testicles of a fire wasp.
- Y Chromosome — In 1905 the Y chromosome was discovered by Nettie Stevens while studying the reproductive organ of mealworms. She named it the Y chromosome to keep the alphabetical order going.

Ch. 18: In the Beginning - Conception and Birth

Sperm — Sperm is heroic: the astronauts of human biology, the only cells designed to leave our bodies and explore other worlds (women). But on the other hand, they are idiots. They are terrible swimmers and appear to have almost no sense of direction. Unaided, it could take a sperm ten minutes to swim across a space the width of one of the words on this screen. Sperm fails to do its job most of the time; the chances of a successful fertilization from a single sex act have been calculated to be only 3%.
Eggs — Interestingly, every woman is born with her lifetime’s supply of eggs already inside her. They are formed when she is still in the womb and sit in the ovaries for years and years before being called into play. A 20-week-old fetus will weigh no more than three or four ounces but will already have 6 million eggs inside her. That number falls to 1 million by the time of birth and continues to fall through life. As she enters her childbearing years, a woman will have about 180,000 eggs primed and ready to go.
- Quote (P. 291): “The bottom line is that as a woman ages, the number and quality of her eggs diminishes, and that can be a problem for those who postpone childbirth to the later stages of their productive years, which is exactly what is happening throughout the developed world… by the age of 35 a woman’s stock of eggs is 95% exhausted and those that remain are more liable to produce faults or surprises, like multiple births. Once women pass 30, they are much more likely to have twins. The one certainty of procreation is that the older both parties get, the more difficulty they are likely to have conceiving, and the more problems they may encounter if they do conceive.”
Zygote & Birth — When sperm does meet an egg inside a woman, the DNA from the sperm and egg are combined into a new entity called a zygote. This is the very start of a new life. Within a week, the zygote produces ten cells known as pluripotent stem cells, which are the master cells of the body and one of the great miracles of biology. These ten cells determine the nature and organization of all the billions of cells that later make up the human. After three weeks, the embryo has a beating heart. After 102 days, it has eyes that can blink. In 280 days, a child comes out.
- Quote (P. 299): “The moment of birth, the starting of a new life, really is quite a miracle. In the womb, a fetus’s lungs are filled with amniotic fluid, but with exquisite timing at the moment of birth the fluid drains away, the lungs inflate, and blood from the tiny, freshly beating heart is sent on its first circuit around the body. What had until a moment before effectively been a parasite is now on its way to becoming a fully independent, self-maintaining entity.”

Ch. 19: Nerves and Pain

Brain & Pain — Oddly, all pain is felt in the brain, but the brain doesn’t have any pain receptors itself. No matter where pain registers (i.e. you stub your toe), the pain isn’t felt until it reaches the brain. In other words, the brain is what makes you feel pain, regardless of where the pain originated.
Nociceptors — Nociceptors are the nerve endings around your body that alert you to pain. When you experience a pain, your nociceptors send “possible threat” signals to the spinal cord and brain. These receptors respond to three kinds of pain: thermal, chemical, and mechanical. Two different kinds of fibers then send the message to the brain and spinal cord:
- A Delta Fibers — These fibers give you the sharp “ouch” of a hammer blow.
- C Fibers — These slower fibers give you the throbbing pain that follows the hammer blow.
Nervous System — The nervous system has two divisions: the brain and the spinal cord. The nerves radiating out from this central hub — the ones that reach out to the other parts of your body — are the peripheral nervous system. The nervous system is additionally divided by function into the somatic nervous system, which is the part that controls voluntary actions (like scratching your head), and the autonomic nervous system, which controls all those things like heartbeats that you don’t have to think about because they are automatic. The automatic nervous system is further divided into two divisions:
- Sympathetic Nervous System — The sympathetic is the part that responds when the body needs sudden actions, generally referred to as the fight-or-flight response.
- Parasympathetic Nervous System — The parasympathetic is sometimes referred to as the “rest and digest” or “feed and breed” system and looks after many other generally less urgent matters like digestion and waste disposal, the production of saliva and tears, and sexual arousal.
Headaches — The brain does not have pain receptors in it and therefore doesn’t have feelings. So where do headaches come from? The answer is that the scalp the face, and the other outer parts of the head all have plenty of nerve endings — more than enough to account for most headaches. Even if it feels as if it were coming from deep within your head, a routine headache is almost certain to be a surface feature.
Opioids — Opioids are painkillers that act in much the same way as heroin and come from the same addictive source: opiates. For a long time, they were mostly used sparingly, primarily for short term relief after surgery or in the treatment of cancer. But in the late 1990s, pharmaceutical companies began pushing them as a long-term solution to pain. They are extremely addictive and have become a real problem, especially in the U.S.
Chapter Takeaway — Regardless of where the pain originates, pain isn’t felt until it reaches the brain. The brain is what makes you feel pain. Pain becomes chronic, rather than acute, when it is constantly being felt. Interestingly, the brain doesn’t have pain receptors inside it.

Ch. 20: When Things Go Wrong - Diseases

Smallpox — Smallpox was maybe the most devastating disease in the history of humankind. It infected nearly everyone who was exposed to it and killed about 30% of victims. The death toll in the 20th century alone is thought to have been around 500 million. In 1980, the World Health Organization announced that smallpox had been completely eradicated, making it the first human disease to be made extinct.
Tuberculosis — With smallpox gone, tuberculosis is today the deadliest infectious disease on the planet. Between 1.5-2 million people die of it every year. About 95% if it’s more than a million and half annual deaths are in low-or-middle-income countries.
Flu Shots — Every February, the World Health Organization and the Centers for Disease Control get together and decide what to make the next flu vaccine from, usually based on what’s going on in eastern Asia. The problem is that flu strains are extremely variable and really hard to predict. 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. H5N1 is the version commonly known as bird flu, and it kills between 50 to 90 percent of victims.

Ch. 21: When Things Go Very Wrong - Cancer

Cancer — At its core, cancer is your body turning on itself. It’s your own body doing its best to kill you. Cancer cells are just like normal cells except that they are multiplying like crazy. Because they are so seemingly normal, the immune system sometimes fails to detect them and doesn’t send 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. All cancers have five main attributes in common:
- Constant Division — They divide without limit
- No Limits — They grow without direction or influence from outside agents like hormones
- Angiogenesis — They engage in angiogenesis, which is to say they trick the body into giving them a blood supply
- Unlimited Growth — They disregard all signals to stop growing
- Spread — They metastasize, meaning they spread to other parts of the body
Cancer Is Resilient — Cancer cells are extremely resilient. Cancer will retreat under an onslaught, regroup, and return in an even more powerful form. 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 a number of things that make it hard for us to kill them.
Cancer & Age — Cancer is above all an age thing. Between birth and the age of 40, men have just a 1-in-71 chance of getting cancer and women 1-51, but over 60 the odds drop to 1-in-3 for men and 1-in-4 for women. An 80-year-old person is 1,000 times more likely than a teenager to develop cancer. Lifestyle, environment, and just complete bad luck can also factor in, but age is the primary thing with cancer.
Cancer Treatments — The three biggest forms of cancer treatment are surgery, radiation, and chemotherapy. Interestingly, chemotherapy is essentially the process of using a derivative of mustard gas to kill cancer cells. In 1943, a U.S. Navy supply ship carrying mustard gas was blown up in battle near Italy. The explosion created a cloud of mustard gas and killed a lot of people living nearby. The Navy sent out an investigator, who found that mustard gas slowed the creation of white blood cells in those exposed to it. This insight led to the belief that some derivative of mustard gas could be useful in treating some cancers. Chemotherapy was born. We are essentially using mustard gas to treat cancer, the same kind of mustard gas that armies used on each other in war.
Side Effects of Cancer — Cancer treatments like radiation and chemotherapy are designed to kill cancer cells, but they don’t target cancer cells specifically. This means there’s a lot of collateral damage. These treatments kill cancer cells AND healthy cells. This is why there are usually bad side effects with cancer treatment; the treatments are killing hair cells, for example, and can also kill other cells in the body and result in bad side effects.
Chapter Takeaway — Cancer is basically your body waging war on itself. Your body is trying to kill you. It’s a terrible thing and seems to be highly correlated with age; older people above the age of 60 are far more likely to get cancer than people who are younger. That doesn’t mean young people are immune to cancer, however. If a cancer spreads, it’s really hard to stop. The best approach is to do everything possible to prevent cancer altogether by exercising, eating well, and getting screenings done early and often.

Ch. 22: Medicine, Good and Bad

Causes of Death — Today, we are much more likely to die of things like heart disease, cancer, diabetes, and Alzheimer’s than we were in the year 1900. This is because the rise of antibiotics, vaccines, and other medications have essentially eliminated death from infectious diseases. In 1900, half of all deaths were from infectious diseases. Today, it’s 3%. We are living longer lives in general thanks to huge advances in medical science in the 1900s.
- Quote (P. 356): “The more or less universal consensus among historians and academics was that medical science somehow turned a corner when it entered the twentieth century and just kept getting better and better as the century progressed.”
- Quote (P. 357): “However we decide to apportion the credit for our improved life spans, the bottom line is that nearly all of us are better able today to resist the contagions and afflictions that commonly sickened our great-grandparents, while having massively better medical care to call on when we need it. In short, we have never had it so good.”
Cost of Medical Care — In America, the cost of medical care is ridiculously high. According to the New York Times, an angiogram costs an average of $914 in the U.S., $35 in Canada. Insulin costs about six times as much in America as it does in Europe. The average hip replacement costs $40,364 in America, almost six times the cost in Spain, while an MRI scan in the United States is, at $1,121, four times more than in the Netherlands. The two drivers of high medical costs for patients? Doctors want to make a few bucks, and doctors are worried about being sued and therefore order sometimes unnecessary screenings.
The Prostate — The prostate is a small gland, about the size of a walnut and weighing just one ounce, which produces and distributes seminal fluid. It is tucked up against the bladder and wrapped around the urethra like a neckerchief ring.
Prostate Cancer — Prostate cancer is the second-leading cause of cancer death for men. The problem is that the test for prostate cancer, the PSA test, is not trustworthy. It ensures high levels of a chemical called prostate-specific antigen (PSA). A high PSA reading indicates a possibility of cancer, but only a possibility. The only way of confirming if cancer exists is with a biopsy, which involves sticking a long needle into the prostate via the rectum and withdrawing multiple tissue samples. Because the needle can only be randomly inserted into the prostate, it is a matter of luck whether it hits a tumor or not. If it does find a tumor, there is no telling with current technology if the cancer is aggressive or benign.
- Quote (P. 363): “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, the majority of them having undergone serious but possibly ineffectual treatments. All this isn’t to say that men should absolutely avoid PSA tests or women breast cancer screening. For all their flaws, they are the best tools available, and they do indubitably save lives. But those undergoing screenings should perhaps be made more aware of the shortcomings.”
  - Takeaway — Although it’s great to get preventative screenings for things like cancer, it’s important to keep in mind that false-positives and other misreading are entirely possible and could lead to an unnecessary procedure or surgery. You have to be aware of this.
Chapter Takeaway — The 1900s are where huge advancements in medical science and treatment were made. Infectious diseases used to be responsible for half of all deaths. Today, they are nowhere near as deadly thanks to the discovery and development of antibiotics, vaccines, and other medications. Now things like heart disease, cancer, diabetes, and Alzheimer’s are the major killers. It’s important to keep in mind that preventative screenings have been known to deliver false readings. These false readings could lead to unnecessary surgery.

Ch. 23: The End

Diminishing Returns — It seems medical science has reached the point of diminishing returns when it comes to aging. By one calculation, if we found a cure for all cancers tomorrow, it would add just 3.2 years to overall life expectancy. Eliminating every last form of heart disease would add only 5.5 years. That’s because people who die of these things tend to be old already, and if cancer or heart disease doesn’t get them, something else will. Eliminating Alzheimer’s would add 19 days.
Lifespan vs. Healthspan — We have become very good at extending overall lifespan (number of years we live), but we haven’t done as great of a job when it comes to healthspan (quality of life). Many people spend the last 5-10 years of their life in agony. It can miserable. That’s why it’s important to take really good care of yourself and build up your strength and cardiovascular endurance in your younger years. By doing so, you give yourself the best chance to feel good late in life.
Telomeres — Telomeres are located at the end of a cell’s chromosome. Each time a cell divides, the telomeres become slightly shorter. Eventually, they become so short that the cell can no longer divide successfully, and the cell dies. Telomeres are essentially “shut off” in cancer cells, which is why cancer cells are able to divide infinitely and experience never-ending growth.
Getting Old — As you get old, many things happen. Your bladder become less elastic which sends you to the bathroom constantly, blood vessels break easily causing bruises, the immune system fails to detect intruders as well as it used to, and the layer of fat directly associated with skin thins, making it harder for old people to stay warm. More seriously, the amount of blood pushed out with each heartbeat falls gradually as we age. If nothing else gets us first, our heart will eventually give out. Because the amount of blood being moved around by the heart falls, our key organs get less blood, too.
- Quote (P. 381): “Getting old is the surest route to dying. In the Western world, 75% of deaths from cancer, 90% from pneumonia, 90% from flu, and 80% from all causes occur in people 65 years of age or older.”
  - Takeaway — Once you hit age 60 or so, things get tough. Your odds of getting some kind of disease and dying increase considerably. It’s critical to prepare your mind and body for this well ahead of time. You have to build yourself up so you can enter this late-stage of life in a good spot.
Alzheimer’s Disease — Alzheimer’s disease is now one of the four top killers. In its normal progression, Alzheimer’s first demolishes short-term memories, then moves on to all or most memories, leading to confusion, shortness of temper, loss of inhibition, and eventually loss of all bodily functions, including how to breathe and swallow. Alzheimer’s first develops when a protein called amyloid-beta builds up in the brain. Sadly, there is still no cure for Alzheimer’s disease, and we still have a hard time definitely diagnosing it. The only way to tell for sure is by studying the victim’s brain after they’ve died. Medications are of no help, either; Alzheimer’s drugs have a 99.6% failure rate in clinical trials.
- Quote (P. 378): “We now know that Alzheimer’s begins with an accumulation of a protein fragment called beta-amyloid in the sufferer’s brain. Nobody is quite sure what amyloids do for us when they are working properly, but it is thought they may have a role in forming memories. In any case, they are normally cleared away after they have been used and are no longer needed. In Alzheimer’s victims, however, they aren’t flushed away but accumulate in clusters known as plaques and stop the brain from functioning as it should. Later in the disease, victims also accumulate tangled fibrils of tau proteins, which are invariably referred to as tau tangles. How tau proteins relate to amyloids and how both relate to Alzheimer’s are also uncertain, but the bottom line is that sufferers experience steady, irreversible memory loss.”
Auguste Deter & Alzheimer’s Disease — The first person to exhibit symptoms of Alzheimer’s disease was Auguste Deter, who in 1901 in Germany checked herself in with a psychiatrist named Alois Alzheimer after experiencing memory loss and just not feeling like herself. Nothing Alzheimer tried worked, and she later died in 1906. Alzheimer studied Deter’s brain via an autopsy and found that her brain was riddled with clumps of destroyed cells. Alzheimer reported his findings in a paper and became linked with the disease, which is why today it’s called Alzheimer’s disease.

Mack's Book Notes

Mack's Book Notes

Mack's Book Notes

The Body

Bill Bryson

GENRE: Health & Fitness

PAGES: 464

COMPLETED: August 6, 2023

RATING:

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Book Notes

Ch. 1: How to Build a Human

Ch. 2: The Outside - Skin and Hair

Ch. 3: Microbial You

Ch. 4: The Brain

Ch. 5: The Head

Ch. 6: Down the Hatch - The Mouth and Throat

Ch. 7: The Heart and Blood

Ch. 8: The Chemistry Department

Ch. 9: In the Dissecting Room - The Skeleton

Ch. 10: On the Move - Bipedalism and Exercise

Ch. 11: Equilibrium

Ch. 12: The Immune System

Ch. 13: Deep Breath - The Lungs and Breathing

Ch. 14: Food, Glorious Food

Ch. 15: The Guts

Ch. 16: Sleep

Ch. 17: Into the Nether Regions

Ch. 18: In the Beginning - Conception and Birth

Ch. 19: Nerves and Pain

Ch. 20: When Things Go Wrong - Diseases

Ch. 21: When Things Go Very Wrong - Cancer

Ch. 22: Medicine, Good and Bad

Ch. 23: The End

Mack's Book Notes

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