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
Because you have organs in your body that have the sole purpose of breaking down and removing substances from your system.
Everything in the blood goes through your kidneys. The way your kidneys work is it pushes absolutely everything then selectively reuptakes the things you need
You answered the question
Homeostasis means your body is on autopilot
So once your body notices it’s no longer on autopilot, it corrects it
Three organs, you liver and kidneys.
Your liver transforms active substances into inert ones.
Your kidneys filter the blood to remove substances.
There are some good answers on here already, but I thought I’d try my hand at summarizing and adding a bit more detail where I could.
As was already mentioned, nothing in the body , natural or not, really “lasts forever.” Everything gets broken down or excreted at some point for some reason like:
* it’s in the wrong body/organ/cell/compartment
* it served its function and needs to be thrown out/recycled
* it’s “old”
* there’s too much of it around
* it’s “labelled as foreign”, etc
And it’s really important for our bodies to have a constant turnover of contents for the sake of maintaining homeostasis like others have mentioned. Usually, it’s detrimental for the body to hold onto too much of anything, even “natural” things. For example, there’s something called haemachromatosis where a person has too much iron in their bodies, which can cause problems. Too much copper can deposit pigmented rings in your eyes and cause other health problems. Same principle applies to just about every other chemical, mineral, fat, protein, etc. Other thing too is that a lot of our body lives in a constant state of simultaneous “break down and building.” For example, in your bones this process is called “remodelling” and helps strengthen them in response to the day-to-day stress you put on them.
As for the second part of your question, how the body knows and gets rid of stuff is a whole field unto itself, and involves a bunch of really cool mechanisms and reactions that our body uses. In short, every cell in your body has some capacity to break down, tag, and/or excrete everything from proteins to chemicals. While your liver and kidneys do the bulk of the heavy lifting, all processes generally involve some combination of:
* breaking down the substance outright or
* chemically reacting on or with the substance to make it easier to dissolve in water (so it’s easier to pass into urine). There are some things in the body that are tagged to make it dissolve more easily in fat to be passed into stool, but that’s a whole other thing
Hope that helps!
Theoretically they do last forever. Since we use a drug’s half-life to determine it’s absorption and excretion, the concentration in your body would approach zero, but never reach it. That’s theoretical though, Usually a drug is considered fully eliminated after 4 or 5 half lives
Pretty sure those chemicals are able to make reactions happen by breaking down/losing part of themselves to the process. I don’t see how a chemical cns serve a purpose in the body while not diluting/dismantling itself over time.
Some chemicals DO last in your system forever, particularly heavy metals. Treating heavy metal poisoning requires chelation therapy – where a chelation agent (which is also toxic) binds to the heavy metals in a way that allows the body to remove both chemicals.
You’re right that most substances eventually leave the body. There are a few oddballs, though, that can build up and cause problems. Think of mercury or lead. Being elements, they can’t be broken down themselves and the body doesn’t do a great job at getting rid of them.
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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