[ELI5]How does the body identify what is bad for you when you consume something toxic and puke it out?

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When you drink gasoline or take a medicine orally with an overdose amount,how does the body identify what is toxic and what is not and then decide if iy should push back or digest it?

In: 9

It dosnt.

Many things are sweet and tasty, lead, antifreeze, poison berries and mashrooms…

the thing is that we have evolved to identify some things, like its hard to get kids to eat veggies as green is a color thats usually asociated with foods that are spoiled or have grown mold.

Your body knows what’s supposed to be in it, and has a bunch of different receptors to make sure it stays that way. For example your body knows you should have about 5L of blood in your body, and that volume creates a certain blood pressure in your body. If you bleed heavily, there is a receptor near your carotid artery that can sense that your blood pressure is low, and if it is, it triggers a bunch of processes to try and get your blood pressure back up, such as telling your kidneys to slow down and keep more water in.

The same mechanism applies to pretty much every other substance in your body, and it’s called homeostasis. It’s just a complicated word that basically means you want to keep things between an upper and lower limit that are acceptable to your body. So say an increase in calcium in your blood below a certain threshold is tolerable, but once you reach the threshold your body does something to correct the situation.

As for vomiting, it can be triggered either by the brain or by the stomach itself, but that’s more rare.

There’s a certain spot in your brain that receives input from various organs in your body and if it gets triggered, it will tell your stomach to vomit. It can be because you ate too much of a certain toxin and your brain goes “oh shit, that probably came from the stomach, better purge that in case there’s more of the toxin in there”. It can also be because you are given medication that confuses your brain a bit such as anaesthetics, and the vomit centre gets triggered without really needing to. Or can also be from motion sickness, when your inner ear and your eyes are sending conflicting signals to your brain (ear says you’re moving, eyes say nuh-uh you’re not) and the brain decides to shut them both up by making you vomit (not a very effective solution but brains are weird like that)

The decision whether to vomit or not depends mostly on the point of action of the poison in your body. Some toxins are active in the stomach already, and your stomach will sense something is off. Your stomach knows approximately which level of acidity it should have and which molecules it should be pulling out of the food. If that’s off, your stomach goes uuuuh I think this is weird, brain what do you think we should do? And the brain usually decides to make you vomit because clearly something in your stomach is messing with your homeostasis limits and making a bunch of alarms go off.

Most toxins however pass through the stomach unnoticed, and only start wreaking havoc when they are processed by the liver. At this stage, vomiting is pointless as the poison is past the stomach already. If you’re lucky, you can still get rid of the toxin inside your intestine by triggering diarrhea, so your body just opens the floodgates and crosses fingers that that will limit the damage. Meanwhile your liver works overtime to try and clear the toxins from your blood. If you’re not lucky and all he poison has been absorbed already, you’ll have to rely on your liver and kidneys to clear your blood from the system, but that can take a while and you will feel the poisons effects in the meantime

I want to know how my guts made an assessment of a bad egg and launched it back up only 5 minutes later. Egg shell had a crack in it and I decided it would be fine. It tasted fine. It was not fine.