If you any active chemical in your system that alters the homoestasis, why does this chemical eventually leave the body? What prevents it from staying in the body forever?
In: Biology
You have a few systems in the body to get rid of everything and then reabsorb things you want to keep.
Your kidneys dump everything possible in your blood into your urine. There is a very fine filter so only small things can get out into the urine and things like red blood cells and large-ish proteins cannot. Then your kidneys reabsorb the good stuff like sugar and electrolytes.
Not everything can be dumped into the urine right away though, lots of things get stuck to the proteins in your blood. And lots of things don’t dissolve in water.
Your liver helps out and has a super advanced system that is designed to try to break down any molecule possible. (It is not perfect though, and sometimes it breaks an outside molecule down into poison.) The liver also helps overcome the water soluable problem by dumping things into your bile which has more fat solubility.
So all in all your bodies strategy is to break down and dump everything and take back only a few specific things. You keep making new molecules that you need from your food, like proteins and blood cells etc. (Even your bones are constantly being replaced at a microscopic level.)
Tl;dr throw everything out, build it from scratch
Ps some drugs *can and do* last for a very long time. Super rat poisons can last in your body for months to years and you have to take superhuman doses of vitamin k, if you even survive at all.
Anything smaller than a certain size is eventually filtered out by your kidneys. They are essentially the spaghetti strainers of your blood with very tiny holes. Small enough that red blood cells don’t fit in them. This is why your pee isn’t red, although it can be. If it is, see a doctor.
Anything larger than that is broken down by enzymes from your liver.
Some stay for the rest of your life, it’s a much shorter life but they stay there because you die, radium comes to mind.
They don’t. Lead notoriously bonds to the molecules in your skeleton and stays mostly for life. Many other toxic chemicals that have cumulative effects don’t get eliminated easily. Lots more compounds are “fat soluble” which means they will persist in your body fat for a long time, as opposed to “water soluble” things that get eliminated relatively quickly.
The ELI5 answer is:
We do. They are classified differently i.e: Poisons.
That’s ecause if the effect is permanent it will by definition render useless whatever it is affecting.
Curare is the easiest example. What it is is a muscle relaxant.
Just a permanent one.
*ALMOST* everything leaves the body eventually. *ALMOST* All of your cells eventually leave after a while, and so do other stuff such as drugs.
Some cells stick around.
Many drugs are broken down by various enzymes that are produced by the liver and excreted. Others just don’t absorb very well from the GI tract and get excreted. Others just get filtered out by the kidney. In pharmacy, we have data for how drugs are broken down, how long it takes, and how the get excreted. The field is called pharmacokinetics, and is very interesting.
Your body has both a conveyor belt and a water slide. Everything has to be moved around the body either as a liquid on the water slide, or as a solid on the conveyor belt. Though some things may take detours to different parts of the body, they eventually have to exit the ride. As more water or solids come in and push them along the path.
Some don’t, but those don’t make good medicines. The only ‘forever chemical’ I can think of that people intentionally take is fluorine, which bonds with your tooth enamel and makes it harder.
Some things do last for years in people’s bodies- like lead when lead is consumed by a child and then bone absorbs (“stores”) it. Then it accumulates and causes bad things
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