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Michael: Everything is chemicals. Your brain, your skin, your blood, your organs, your entire body is made of chemicals. Some you might’ve heard of before, like the neurotransmitter dopamine, which helps you feel happiness and motivation, among other things. Others don’t get talked about as much, like alpha-ketoglutarate, which helps you make energy. And every day, your body produces some chemicals that you might find surprising -- ones you’d usually think of as poisons, or workout supplements, psychedelic drugs, or even embalming fluid. They might sound strange or even harmful, but they’re an important part of how your body works. And in some cases, we probably wouldn’t even survive without them.

First up is formaldehyde, a molecule best known for preserving dead things -- like animals in jars, or even human corpses. Formaldehyde is great at this because it locks a bunch of cellular components together in a process called fixation, which stops any chemical reactions and makes tissues more rigid. This slows down any decomposition and kills off stray bacteria. Formaldehyde solutions are so good at preserving dead bodies that funeral directors keep using it, even though it’s known to cause cancer after prolonged exposure. So too much formaldehyde isn’t very good for you, but your body does need a small amount of it to work properly. Your cells normally produce formaldehyde during some metabolic processes, where they break down molecules and build up new ones. For example, you convert formaldehyde into a compound called formate, which helps make the nucleic acids adenine and guanine -- two of the four building blocks of DNA. Some gets broken down further and peed out or exhaled, but normally there are at least a couple micrograms of formaldehyde floating around in your blood.

Small amounts of acetone are also naturally found in your blood and urine. You might know acetone as the active ingredient in nail polish remover and paint thinner. And, at high concentrations, acetone can cause skin rashes and irritation. But your body also makes acetone when you’re desperately in need of energy. Usually, most of your energy comes from carbohydrates -- like glucose that’s in your food or stored in your cells. But when you do a lot of exercise, or if you’re on a low-carb diet, your body starts making energy from other sources -- like by breaking down fats in different ways. And when your body breaks down fats without much glucose around, it produces compounds called ketone bodies.

One of those compounds is acetoacetate, which can break down further into acetone. Your body doesn’t really use acetone for anything, so it mostly tries to get rid of it. In fact, if you have too much acetone hanging around, it can make your blood acidic, which is not great This is more of a risk for people with type 1 diabetes, who have a harder time getting glucose into their cells, and rely more on the synthesis of ketone bodies for energy. Some of that acetone leaves your body when you exhale, and people with too many ketone bodies may even have a “fruity” smell to their breath from breathing out so much acetone. But mostly, you just get rid of extra acetone in your urine.

Hydrochloric acid is one of the strongest acids out there. Highly concentrated solutions can dissolve some metals, and it can cause severe burns if it gets on your skin. That dangerous dissolving power is precisely why your body makes it. We eat food to get lots of different nutrients -- things like glucose, fats, amino acids, and vitamins. However, these simple compounds that our cells use are usually trapped in more complex molecules. Plus, a lot of bacteria tend to hitch a ride on our food, since they want the nutrients, too. So to break down our food and kill a lot of that bacteria, our stomachs us the power of Hydrochloric acid.

Stomach acid has about the same pH as battery acid, so it’s plenty strong enough to break down all kinds of molecules in your food. It’s also strong enough to break down the proteins in the cell walls of your stomach... and you don’t exactly want your stomach eating holes in itself. For protection, our stomach cells generate a layer of mucus that’s full of bicarbonate ions, which acts as a physical barrier that also neutralizes the harsh hydrochloric acid. So, in some sense, your stomach is locked in a perpetual battle with itself so it can get you the energy you need to stay alive.

Hypochlorous acid is weaker than hydrochloric acid, but it’s still not something to play around with. Hypochlorous acid is the active ingredient in a lot of household bleaches, and it’s also in a lot of disinfectants because it’s so good at killing bacteria. Bacterial cell walls are often negatively charged, which means that they repel any potential harmful molecules that also happen to be negatively charged. But hypochlorous acid is neutral, so it’s able to slip right past the defensive wall and start messing with the proteins inside, or even start breaking the wall itself. Since cells don’t really do so well without working proteins, the bacteria die. Your body uses hypochlorous acid for the same reason. The white blood cells in your immune system protect your body by seeking out invaders like viruses and bacteria. Then, they engulf the intruder and use hypochlorous acid to kill it. So when you clean off your counters at home, you’re disinfecting just like your white blood cells do.

Despite what you might have learned about Hydrogen peroxide when you were little, you probably shouldn’t be using it to clean up wounds because it kills whatever it touches, including the cells that are trying to help you stop bleeding. But whether you put it there or not, you’re going to find some hydrogen peroxide around a new cut, because that cut makes your cells release it naturally. The burst of hydrogen peroxide acts like a big “Please send help!” signal -- so your body sends platelets and other cells to start blocking up the wound. Plus, it sends a flock of white blood cells to kill any bacteria.

Citric acid is responsible for that bitter taste in oranges, lemons, limes, and lots of other citrus fruits. It’s also used to add a tang to lots of sodas, and it’s often used to make sour candy sour. Your cells make citric acid as part of the process that turns everything that you eat -- carbohydrates, proteins, and fats -- into energy and carbon dioxide. The citric acid gets put into the citric acid cycle, also known as the TCA cycle, or the Krebs cycle... or just as that thing everybody hates memorizing for bio class. Ammonia is a base, unlike all the acids we’ve talked about so far. It’s used as a fertilizer, and it’s also in a lot of cleaning products because it’s good at breaking down fats and oils. But your body also produces ammonia when it metabolizes proteins -- and so do a lot of the bacteria in your digestive system. Your body uses some of that ammonia in your kidneys -- the ammonia bonds to hydrogen, which helps stop too much acid from building up. Your liver then turns any extra ammonia into urea -- one of the main components of urine -- and gets rid of it as waste.

Now, let’s talk about drugs. Specifically, endocannabinoids. Cannabinoids may sound familiar, because some of them are the main chemicals that interact with receptors in people’s brains when they use cannabis -- or pot, as the kids are calling it these days. Endocannabinoids are compounds your body makes that work on those same receptors. Their main purpose seems to be reinforcing energy-storing behaviors by making them pleasurable -- like eating fatty foods. The compounds are even found in the developing brains of babies -- and in breast milk. They probably keep babies more interested in eating, and in eating more often -- like a chemical appetite booster to keep them well-nourished.

Endocannabinoids are nothing compared to a much more intense compound called dimethyltryptamine, or DMT. DMT has been called “the most powerful hallucinogen known to man and science.” Unlike everything else we’ve talked about, scientists aren’t quite sure why your body makes such a powerful psychedelic. It’s been detected in trace amounts in human blood, urine, and cerebrospinal fluid, and it’s probably some kind of byproduct. It’s possible that DMT is produced by our brains, and, if that’s the case, it might help our brains calm down. But the research so far has mostly been inconclusive, so nobody knows for sure.

We’ll wrap up today with creatine, a compound that a lot of people use as a workout supplement. Creatine is typically stored in your body as the compound phosphocreatine -- which is just a phosphate group bound to a creatine molecule. Phosphocreatine makes itself useful by donating its phosphate to create more of the ATP molecules that keep your muscles going. That’s why people consume creatine as a fitness supplement: it can give you a little bit of extra energy during intense muscle activity. In your body, creatine is normally made in your liver, kidneys, and pancreas from parts of the amino acids glycine, arginine, and methionine. From there, it’s distributed to your muscles through your bloodstream and converted into phosphocreatine, where it sits and waits until you need a burst of energy. Different people naturally have different levels of creatine in their systems. So people with lower levels may get more out of taking creatine supplements, but people who naturally synthesize more don’t really respond very much to it. Their bodies just don’t need the extra help.

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