The Body

The Body, a guide for occupants is a book written by Bill Bryson in which he covers different parts of the human body, providing interesting facts.

He intersperses raw facts with personal narratives, often telling the story of individual scientists involved in their discovery, or a notable patient that suffers a condition related to the topic.

Instead of trying to summarize, I’ll just list bullet points from my notes of things that I learneda and found interesting.

How to build a human

There are 100k to 1M types of proteins.
Only 2% of DNA codes for proteins.
We have 37 trillion cells.
Nearly all animals produce their own vitamin C, but not humans.

Skin and hair

Skin is the thinnest at eyelids and thickest on heels.
Pimple vs. acne: acne is the chronic condition.
We don’t have sensor for wetness, only temperature.
Melanin is what gives color to bird feathers.
Hair is exclusive to mammals.
Sweat is activated by adrenaline. Palm sweating doesn’t get triggered by exercise but stress.
There are two different types of sweat glands: aprocrine (armpit) and eccrine (elsewhere).

Microbial you

Bacteria only lives for 20 minutes on average.
There are roughly the same number of cells and microbes in our body.
Red blood cells are not true cells: no mitochondria nor nuclei.
There are 1.5k types microbes that can make us ill, account for ⅓ of the diseases.
Archae isn’t known to cause diseases.
Only 263 viruses affect humans.
Most common way to get cold viruses is through touch.
Julius Richard Petri (of the dish fame) was a student of Robert Koch (nicknamed the father of microbiology). The idea of using agar came from his lab too.

The Brain

Quote on our brain predicting the short term future:

One-fifth of a second is not a trivial span of time when a rapid response is required-to step back from an oncoming car, say, or to avoid a blow to the head. 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.

Another good quote by James Le Fanu on adding meaning to sensory information:

While we have the overwhelming impression that the greenness of the trees and the blueness of the sky are streaming through our eyes as through an open window, yet the particles of light impacting on the retina are colourless, just as the waves of sound impacting on the eardrum are silent and scent molecules have no smell. They are all invisible, weight-less, subatomic particles of matter travelling through space. All the richness of life is created inside your head.

Researchers sometimes categorize memory into recall memory (e.g. when answering a trivia quiz) and recognition memory (when things are hazy but we recognize context).

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, the color or design of the cover, and other seeming irrelevancies/ Recognition memory is actually useful because it doesn’t clutter the brain with unnecessary details but does help us to remember where we can find those details if we should need them again.

Gray matter and white matter are named after their appearances when dissecated, but don’t have those colors when alive.
Lobotomy was invented by a Portuguese guy, António Egas Moniz, who was awarded Nobel prize.
Epilepsy is the chronic condition of having seizures, which means neuron misfiring.

Head

We cannot fake smiles because we don’t have control of the muscles in the eye.
People have more trouble identifying celebrities missing eyelids that eyes.
Papilla lacrimalis is the knot at the corner of our eyes and act as a drain.
Ancestor of mammals was nocturnal, so it sacrificed color for night vision. Primates re-evolved some color receptors, but birds have 4 color receptors.
A significant part of what you actually see is imagined.
Bones of the inner ear evolved from jaw bones
Acoustic reflex - to protect our hearing, when a sounds is too loud, the stapes (inner ear bone) gets disconnected from the cochlea - that’s why we feel deaf after a loud concert.
Cilia for detecting higher frequency is in front, so they wear out first as we age.
Brain interprets loss of balance as poisoning, hence we feel nausea.
We have 300-400 receptors for smell.
About 70% of people who lose the sense of smell from the flu never recover from it.

Mouth and Throat

We have taste receptors in gut and other places but not connected to brain. Maybe useful for detecting toxic substances.
Pepper developed spiciness to protect against small mammals who destroy their seeds - birds swallow seeds and spread them via poop so there’s no defense mechanism agaisnt them.
Flavor vs taste: flavor is done by nose (e.g. strawberry flavor).

Heart and Blood

A measurement of 120/80 for pressure represents the highest (during contraction) and lowest (relaxation)
Heart attacks more common in the dead of the night
Bradycardia is slow beating, tachycardia is fast beating
Heart attack is when oxygen can’t get to rest of the body (e.g. due to clogged artery). Heart arrest is when heart stops beating.
Heart attacks can happen to healthy people.
The sale of blood plasma accounts for 1.6% of US exports.
The blood type O was meant to be 0 (because it didn’t clump when mixed with other blood types).

Chemistry department

Hormone is defined as substances produced in one place and used elsewhere.
Puberty starts early nowadays, possibly due to nutrition.
NAFLD stands for No-Alcoholic Fatty Liver disease (⅓ of us have, associated with obesity).

Skeleton

Cartilage is smoother than ice
The hands and feet alone have more than half of the bones in the body.
Bones produce hormones too: osteocalcin.
Bones grow thicker with use.
Tendons: muscle to bone, ligaments: bone to bone.
Three muscles in the thumb that sets us apart from all other animals
“We enter the body through the pelvis and leave it though the hip”, because 30% of elderly who break hips die within 1 year.

Locomotion

We first started walking and only about 4 million years later started running. Lucy the ape could not run.

Equilibrium

A child half my height would suffer 32x the impact of a fall?
Children cannot handle heat well because their sweat glands is not fully developed.
Unit 731 was a secret research center by the Imperial Japanese Army that did biological and chemical experimentation on prisoners in China. It was kept in secret until 1984.

Immunity

Allergy to penicillin is a common cause of anaphylaxis

Lungs and breathing

Our nose runs because hot air from the lungs meet cold air from outside and condensates.

Nutrition

Roughage is a synonym for dietary fiber
On average, about 6% of weekly income spent on food today, compared to 50% a century ago.

Digestion

Food gets fermented in the colon where bacteria process dietary fiber we cannot digest.
Stomach is helpful but not essential. It kills pathogens with hydrochloric acid.
The sound made by the stomach has a name: borborygmi.
Most food poisoning takes 24h to act, so when we get reactions, it’s not the last thing you ate.
Most of the digestion happens in the small intestine. Colon is another name for large intestine.
Western diet is more likely to cause colon cancer, while Eastern diet is more likely to cause stomach cancer.
About ⅔ of people don’t produce methane in fart. It’s dangerous to lit fire near the anus, it could explode the colon.

Sleep

Hibernation is different from sleep. In fact, there’s sleep within hibernation. Bears don’t hibernate.
We turn 30-40x a night.
We have brightness receptors that tells us whether it’s day or night and it’s independent of vision (blind people can detect it too).
People in coma can yawn.

Sex

Chromosomes were named after how easily they absorb dyes (color, chroma) in the lab.
The X chromosome was named because it was a mystery. Y chromosome named after X.
Epididymis is a fine tubing coiled in the scrotum where sperm matures

Birth

The word sperm was first recorded in English in the Canterbury tales.
Chances of having twins increases after the age of 30.
According to studies, women forget about the pain of birth so to not prevent them from having subsequent babies.
After birth only the liver, brain and immune system remain plastic.

Nerves and Pain

There’s no specific area in the brain for processing pain.
Pain and touch signals are send over by different types by never fibers. So pain is not just a touch with stronger intensity.
Chronic pain serves no apparent purpose.
Internal organs and brain don’t have pain receptors so headaches are external like scalp or face.
Migraine comes from the French demi-craine (half-skull).
Opioid crisis has led to increase in organ donation.
The word placebo used to mean sycophant (from Latin “to please”).

Diseases

An infectious disease is one caused by a microbe. A contagious one is transmitted by contact.
Diphtheria comes from the Greek “leather”, due to the appearance of the coat formed by dead cells in the throat.
Smallpox vaccine doesn’t last for life.

I believe this book was written before the Covid-19 pandemic, so these quotes from Michael Kinch are prescient:

In the event of a really catastrophic epidemic-one that killed children or young adults in large number (…) we wouldn’t be able to produce vaccine fast enough to treat everyone, even if the vaccine was effective.

And:

We are really no better prepared for a bad outbreak today than we were when Spanish flu killed tens of millions of people a hundred years ago. The reason we haven’t had another experience like that isn’t because we have been especially vigilant. It’s because we have been lucky.”

Cancer

½ men over 60 and ¾ over 70 has prostate cancer at death (many undiagnosed).
Types: carcinoma happens in epithelial cells including lining of organs and accounts for 80% of cancers. Sarcomas happen in connective tissue.
Ernest Lawrence, inventor of the cyclotron and after which the Lawrence Berkeley National Laboratory is named, discovered that shooting X-rays could be a cancer treatment, by trying on his mother.
Chemotherapy uses a variant of mustard gas for treating cancer.

Medicine good and bad

Albert Schatz and the streptomycin
There are 11 traffic deaths per 100k people in the US, compared to 4.3 in Japan (I’m actually surprised the difference is not larger).
Mammogram screening is not that effective: it improves death rate from 5/1000 lives to 4/1000, with similar rates for prostate cancer.

Death

We are one of the few land animals that go through menopause. The “land” qualification is needed because apparently many types of whales do too.
Only 1 in 10k people are reach past 100.
The condition that Alois Alzheimer originally described in 1906 is not exactly the same as what we now broadly call Alzheimer’s disease. It was a genetic condition called metachromatic leukodystrophy.
Today, about 40% of Americans are cremated while 75% of Brits are. A hundred years ago it was about 1%.