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
On a very general level: entropy. “Active” chemicals have energy stored (think of it like being under tension) and will fall apart on their own to get into a more relaxed state. Everything in nature is constantly falling apart and it takes effort to counteract that.
There are many sensors in the body checking whether everything is in balance, if it’s not, it gets corrected. Too much water in the bloodstream and the kidneys will get rid of that asap.
Some drugs simply get washed out that way. They get strained through the kidneys and not actively held back. Mannose is a sugar that goes that route. Through the intestinal wall into the blood stream, no one and nothing needs it, wants it, or even just interacts with it by accident, and out the kidneys it goes. Just something passing through.
Many drugs are actually made to be broken down and eliminated. Or even broken into its active form, then broken down and eliminated. All the blood from the intestines first gets filtered in the liver. It has a whole battery of enzymes (molecules that change others, like a machine in a production line, they stomp things into shape, cut something off, assemble something else, each enzyme does a different step). The enzymes will process anything with the right shape, it fits, it sits, and gets a make-over. So drugs either need to be built to not get mangled in the liver, or at least so that some of it manages to get through (with some drugs 80% of the stuff gets chewed up in the liver before ever going anywhere) OR, you make the liver work for you, and let it transform an inactive substance into the actually active drug. Very elegant.
You want to be able to modify when/how/how long a drug works. If an anesthetic works indefinitely, whoops you just put someone in a coma. It’s better to have a drug that works as fast as a light switch for that. Consciousness off, procedure done, consciousness back on. A substance that gets broken down this quickly has to be applied constantly for as long as its supposed to work, but that’s better than not knowing how long a patient will be knocked out and sitting there for hours waiting for them to wake up.
There are substances that do not leave the body, or some people do not have the necessary equipment to get rid of them (lack of the correct enzyme f.ex.) That’s bad news. The stuff needs to be put somewhere and accumulates under the rug or in a dark corner until it becomes a serious problem. Heavy metals can break enzymes faster than the body can make new ones f.ex. or the deposits get so big that they’re in the way of normal everyday functions. People who drink lots of colloidal silver can turn smurf blue. It’s more than the body knows what to do with, so it shuffles it into the skin.
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