As I got up to make another cup of tea and to hit the john, I started wondering:
You need to keep hydrated because your body needs water to do {whatever it is that your body needs water to do}. How much of the liquid that you consume is used for these various biological purposes?
Specifically, if you drink, say, a liter of water, how much do you pee out vs. how much does your body absorb for its own use?
I’m no expert but I never thought of it that way. Even the water expelled in your urine is helping to flush away waste products.
Your body tries to maintain a certain salinity and your water weight will change in response to that and other chemical issues.
So if you drink a liter of water, in an ideal situation you pee all of it out less any water shed through perspiration.
Maybe I misunderstand your question.
None of the water is absorbed by cells or used up in other biological processes? If you’re not sweating, you pee out 100% of the water you drink?
Huh.
There are a few biological processes that either create water or split it into something else: photosynthesis and dehydration synthesis, for instance. I’m guessing you don’t photosynthesize, but any time you add a monomer to a growing polymer, you create a water molecule, and any time you depolymerize something, you use up a water molecule. Generally, the balance between those two processes should be pretty close to equal, so it wouldn’t have a huge affect.
Everything else is simply moving water around physically - from your gut to your bloodstream to your kidneys to your bladder. Or secreted as sweat, or breathed out through your lungs as vapor. You need a lot of water in your body, obviously, but it’s mostly just there as a solvent rather than as a reagent.
Ah. Okay.
Thanks!
If you weren’t sweating or peeing, or experiencing other water loss, the cells would have no need to absorb additional water. All of the water you drink passes through one or more bodily systems, but it’s impossible to distinguish between water that was absorbed by the gut, passed into the bloodstream, and eliminated directly through the kidneys, and water that was absorbed by the gut, passed into the bloodstream, and was absorbed by cells to replace water that was eliminated into the bloodstream by those cells. (Well, it’s not impossible, but I think you’d have to drink unsafe amounts of tritiated water.)
Your body is a net producer of water. The idealized description of animal metabolism is that you take in compounds composed mostly of carbon, hydrogen, and oxygen as food, and elemental oxygen from the air, and “burn” the food to produce carbon dioxide and water. So your water out is definitely greater than your water in.
That said, I’m not sure what proportion of that water is excreted via the lungs, skin, or kidneys: It’s certainly possible that you might pee less than you drink/eat.
Your body can use it and then eliminate it. I always think of drinking water as taking an internal shower. Well, I had to do something to make the idea of all that water palatable! But anyway, the shower water washes you, then all runs down the dram.