A fun fact from each chapter…
- How to Build a Human: You can buy the elements to build a human for ~$150,000 (or $168, depending on your calculations).
- The Outside: Skin and Hair: The outermost layer of your skin, the stratum corneum, is made entirely of dead cells and is replaced in about a month.
- Microbial You: Potential new mechanism for antibiotics is disrupting bacterial communication, perhaps by targeting quorum sensing signals, since bacteria don’t “attack” until sufficient numbers are assembled.
- The Brain: In a single cubic centimetre of brain matter, there are more synapses than stars in the Milky Way.
- The Head: The smile is a true universal expression; real smiles involve the contraction of the orbicularis oculi muscle in your eyes, which you don’t have independent control over!
- Sight: When you see white “stars” when looking at a blue sky, it’s actually your own white blood cells getting stuck in capillaries (blur sky sprites, or officially, Scherrer’ about field entropic phenomena).
- Hearing: Our hearing is so sensitive that we can sense a sound wave produced by something moving the width of an atom— literally as good as it could be.
- Smell: Two theories for how molecules activate their specific olfactory receptor are by shape (lock and key), or, more interestingly, by resonance of their vibrations.
- Down the Hatch: The Mouth and Throat: Taste receptors are found all the way down the throat and in the stomach, and even in the heart, lungs, even testicles— but the ones not in the mouth don’t send signals the same way to the brain, so you don’t actually perceive the taste.
- The Heart and Blood: During a lifetime, the heart does enough work to lift a one-ton object 150 miles into the air.
- The Chemistry Department: To recall facts about the spleen, remember 1, 3, 5, 7, 9, 11— it is about 1x3x5 inches in size, 7 ounces, and lies between the 9th and 11th ribs.
- In the Dissecting Room: The Skeleton: Bones produce the hormone osteocalcin, associated with regulating glucose levels, mood, and fertility, as well as maintaining memory. This could be the mechanism for how exercise is protective against Alzheimer’s: impact builds stronger bones, which produce more osteocalcin.
- On the Move: Bipedalism and Exercise: The heart, the brain, and kidneys burn about 400 kcal per day each, and the liver 200. Just standing burns about an extra 100 kcal per hour, and walking around 180.
- Equilibrium: Almost all animals have about 800 million heartbeats over their lifespan… except humans these days, who reach about 2.4 billion. This relates to body size because larger volumes have less relative surface area and thus require less energy to maintain their heat, so heart rate is lower.
- The Immune System: Rates of autoimmune diseases are skyrocketing: Chron’s has gone from affecting 1 in 50,000 people in 1932 to 1 in 250 today, while the percentage of people with peanut allergies has quadrupled since 1999 to around 2%.
- Deep Breath: The Lungs and Breathing: In all likelihood, with one day’s breathing you will inhale at least one molecule from every person who has ever lived, and every person that will ever live from now until the sun burns out (each exhale is 25 sextillion molecules!).
- Food, Glorious Food: The average fruit in the 1500s was only as sweet as a modern carrot.
- The Gut: Stool samples from the same person can have vastly different microbial compositions just a few days apart— or even samples from two ends of the same stool!
- Sleep: There are special (third kind of) photoreceptors (photosensitive RGCs) in your eye that specifically detect brightness and send signals to the superchiasmatic nucleus, thus affecting the circadian rhythm. They are completely independent of sight
- Into the Nether Regions: The X and Y chromosomes were not actually named after their shapes, and it’s a coincidence that they resemble their letters! The X chromosome was named so because it was mysterious, and the Y to follow it alphabetically.
- In the Beginning: Conception and Birth: There is some evidence that a mother absorb some of her baby’s saliva through her breast duct when nursing, which is “analysed” by her immune system, which then responds by adjusting the amount and type of antibodies supplied to the baby.
- Nerves and Pain: Signals from pain are transmitted by two kinds of fibers— fast-conducting delta A fibers that are coated in myelin which give you the initial sharp pain, and slower-acting C fibers that give you the throbbing pain after.
- When Things Go Wrong: Disease: There are 800,000 viruses in birds and mammals with the potential to adapt to humans and cause infection… Flu strains are named HXNY depending on which iteration of two surface proteins they have (hemagglutinin and neuraminidase).
- When Things Go Very Wrong: Cancer: Just after the discovery of radium in 1898, the element was added to medicines (and people drank it!) before it was found to literally dissolve people’s bodies.
- Medicine: Good and Bad: A 30 year old black male in Harlem, New York is at much greater risk of dying than a 30 year old male Bangladeshi, not from drugs or violence by heart disease, cancer, or diabetes.
- The End: Free radicals are wisps of cellular waste built up by metabolic processes that contribute to degeneration. Ultimately, then, the biochemical price of breathing is aging.