You’re a human. You poop (nearly) every day, and you puke, sure, but it’s rare, even though your body actually has so many reasons to do so. Pooping and puking are two totally disgusting, sometimes therapeutic body expulsions. But why do you do them and how do they work?
No, we’re going to not lounge about in the high-level explanation (it’s your butt and your mouth, people). Let’s jump right into the cool science stuff!
Pooping is the process of expelling all that stuff inside you that, hey, you don’t need. It’s a periodic upkeep of the body. Though your waste is mostly made up of water, its somewhat solid quality is due to the rest of it being made up of dead and living bacteria, protein, fiber, plenty of bogus things like salts and fats, and a score of things from the intestines and liver. Whatever your porcelain throne-room sit-down schedule is, pooping is normal. Keep it regular, yo.
Diarrhea, on the other hand, is the nasty business of food and fluids passing through your colon way too fast. Your colon typically absorbs liquids, leaving that usual fecal matter you should honestly be accustomed to by now. But sometimes that doesn’t happen for several reasons.
Viruses and bacteria can naturally wreck up your internal pre-poop process, but so can certain medications, as they disrupt the natural balance of bacteria in your intestines. If you can’t digest it, whether it’s fructose or lactose, diarrhea’s on its way. It’s never pretty.
Inside your head, there’s a doctor of sorts—well, more of a toxin specialist, really—called the area postrema. Your brain, the beautiful complex maniac that it is, walls itself safely away, kind of like a glorious, magnificent kingdom (if it were run by emotionally unstable academics). That protection’s thanks to the blood-brain barrier. That’s except the area postrema, however, which stays exposed to the bloodstream. By doing so, it scans your blood for toxins, and because it’s damn good at its job, it’ll frantically slam the alert button if it finds something it doesn’t trust, forcing your body to spill its guts to prevent any possible future damage.
But that’s just toxin puke. There are other kinds of puke. There’s the gag-reflex puke, which is when you trigger the vagus nerve. There’s the too-full puke, which is when you upset your stomach’s nervous system (likely by overeating). There’s stomach-irritation puke, which is when you legitimately get sick and your stomach just goes scrambly haywire, suddenly unsure how to act. And then, well, there’s emotional puke, where your body has such a hard time determining if the stress you’re rampaging through is physical or emotional, so it goes with the default of puking, just in case.
Sometimes, because it cares so freakin’ much, your body can overreact. So when a very notable chemical change sweeps through you, the body pretty much makes you puke to be on the safe side. Such is the case with pregnancy and chemotherapy (as if the person wasn’t going through enough already).
Yup, this is a thing that happens to a small segment of the population. It can only occur after substantial constipation, usually due to an intestine-blocking parasite, but it’s not quite feces these unfortunate folks are bringing back up. In reality, the contents of the first section of their small intestine attempts to expel waste/the grubby freeloader(s) in the other direction. If you ask anyone who’s experienced it, however, it’s poop.
And there you have it, the astoundingly gross wonders of your resilient body!