Like, what exactly happens when you take a pill of vitamin A compared to vitamin D? Or a tiny grain of fentanyl? How exactly do our body recognize these extremely complex substances and not confuse one from another?
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They do confuse each other. All the time.
You mention fentanyl. Fentanyl is an opioid, meaning it acts on the opioid receptors. These are little receotora on the nerves that activate upon contact with endorphins, and on activation it calms the nerves, makes it harder for the nerves to send signals, like to send a pain signal. Sometimes it’s necessary for the body to increase its pain tolerance so the brain releases endorphins into the blood which acts on all nerves throughout the body.
Fentanyl tricks the opioid receptors by looking like natural endorphins but not actually being one. It’s actually more powerful than the natural ones because endorphins are a lot bigger cause they were made through the imperfect process of evolution, fentanyl is much smaller but fits into the part of the opioid receptor that matters and is better at triggering it. It’s a mistake that fentanyl works here, but there’s been little evolutionary need to prevent this so it just happens. And even if there was an evolutionary need to, there are a lot of chemicals out there, many which still fit the lock here.
So the actual thing often recognized isn’t the entire substance, it’s the individual pieces that make it up. When you start dealing with big molecules like proteins a lot of their parts start to look alike and we have proteins, little chemical machines, that can recognize these parts, not just the individual molecules, and deal with them however it needed to be dealt with.
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