What if urine was reprocessed by large intestines?

Submitted ⁨⁨1⁩ ⁨year⁩ ago⁩ by ⁨Thurkeau@lemmy.world⁩ to ⁨nostupidquestions@lemmy.world⁩

I have wondered many times how a human would fare if the kidneys dumped urine into the start of the large intestines somewhere about the appendix instead of into a bladder to be sprayed out. I’m assuming water would be reabsorbed and slower to process out, primarily through sweat and evaporation from the lungs, and maybe diarrhea, though it may be that other waste products, such as salts or ureas may be absorbed into the large intestines instead of being ejected, though I have no idea if it would, or if it would be ejected as intended. Do we have any biologists here that could give insight on if combining both waste paths into one would be advisable?

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readyno@lemmy.world ⁨1⁩ ⁨year⁩ ago
Am doctor, you are essentially asking about a fistula (abnormal communication) that would allow urine and bowel to mix. This would allow for communication of gut bacteria to then invade the urinary system which would then easily cause a kidney infection which would then seed the blood resulting in bacteremia. Bacteremia is bad, like you die from infection unless you are on IV antibiotics and get the source under control bad. As an example, colovesicular fistula is a communication between the colon and bladder which often results in bad infections and needs to be surgically repaired. Hope this helps.

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- Delphia@lemmy.world ⁨1⁩ ⁨year⁩ ago
  Ok but why cant I have a secondary urethra grafted in that runs in my leg down to a nice discreet exit on my ankle so I can take a sneaky wee when Im out and about.
  
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  - finthechat@kbin.social ⁨1⁩ ⁨year⁩ ago
    You could just tape a garden hose to your dick and run it down a pant leg. Man, I should patent this idea....
    
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  - Thurkeau@lemmy.world ⁨1⁩ ⁨year⁩ ago
    Then you’d be right back where you started for my purposes, still losing moisture unnecessarily.
    
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- HeyThisIsntTheYMCA@lemmy.world ⁨1⁩ ⁨year⁩ ago
  No he’s asking what if humans had cloacas
  
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- Thurkeau@lemmy.world ⁨1⁩ ⁨year⁩ ago
  I can totally see that, though what if the body was able to adapt to the new configuration and keep the gut bacteria in its place, but the urine still flowed into the bowels for reprocessing? What else would the large intestines pick up aside from water and maybe salt?
  
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  - Rin@lemm.ee ⁨1⁩ ⁨year⁩ ago
    There’s not much in urine except water, maybe a little bit of sugar if you’re diabetic. I don’t think this would be a beneficial adaptation. I’m pretty sure that if this was advantageous, it would have been adapted way earlier in our evolution.
    
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Rivalarrival@lemmy.today ⁨1⁩ ⁨year⁩ ago
Consider, for a second, what would happen if and when the pressure in the colon exceeded the pressure in the bladder, and a urethra connected the two: fluid in the colon would backfeed into the urinary tract. The kidneys would ultimately be exposed to intestinal flora.

The prevalence of UTIs even with the “air gap” of separate waste streams tells me that this would be an extraordinarily bad idea.

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- Chetzemoka@startrek.website ⁨1⁩ ⁨year⁩ ago
  Can confirm, there is a condition that removes the air gap causing a pretty much continuous UTI. (Colovesical fistula: www.wakemed.org/…/colovesical-fistula)
  
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redcalcium@lemmy.institute ⁨1⁩ ⁨year⁩ ago
Then you’ll basically have a cloaca, and perhaps you’ll ended up like bird and reptile which can’t seem to hold their shit and also have watery shit. One of the great things about mammals is they’re able to hold their (relatively) dry shit until they found a safe place to dump it.

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- Catoblepas@lemmy.blahaj.zone ⁨1⁩ ⁨year⁩ ago
  That might be a trainability issue rather than a physical capability issue, the more intelligent parrot species are able to be trained to defecate either on command or in specific spots.
  
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LackingC10H12N2O@lemmy.world ⁨1⁩ ⁨year⁩ ago
I have Crohn’s disease and therefore already pee out of my a$$ on a regular basis.

0/10 would not recommend.

(obv. not exactly what OP is asking but it i imagine feels the same)

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- elementalguy2@lemmy.sdf.org ⁨1⁩ ⁨year⁩ ago
  Ditto. I had my large intestine removed and now adding even more liquid would not be pleasant.
  
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_haha_oh_wow_@sh.itjust.works ⁨1⁩ ⁨year⁩ ago
Well, then urine trouble because that would be like having liquid poo all the time. Gross.

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BananaTrifleViolin@kbin.social ⁨1⁩ ⁨year⁩ ago
So the way evolution works, the design we have works well enough that it doesn't cause problems. It might be the best possible design or it might not, all that mattered is that whenever it arose in evolutionary history it was either an advantage over what camebefore in terms of survival so propagated or it was not detrimental and paired with something else genetically that propagated.

We can't definitively answer your question but we can speculate on why it's a good idea to separate urine and faecal matter. Urine is a reasonable medium for growing bacteria. That wouldn't matter in the colon but would matter if bacteria from the colon could ascend into the kidneys and diarupt it's function. Valves could help or a bladder that drains into the colon, but complete separation may just be better.

It may also be that the acidic nature of urine would disrupt the helpful bacteria we rely on to colonise our guts to help digest foods.

Another possibility is the constant flow of urine would mean our faecal matter would never dry out. It'd be like having diarrhoea all the time and we'd need to poop constantly. The colon retrieves enough water - but not all water - that's why poop isn't hard as rock. If it was flooded with fluid it may not need to retrieve fluid.

The fluid might even be stuck in a cycle between the colon and the kidneys and make it harder for the body to keep homeostasis - as the kidneys excrete more fluid to try and regulate fluid volume the the colon could just resorb it. Basically the colon could end up working against the kidneys and cause even more work for thenl body. It may just be less efficient than discarding water as needed.

Drier faecal matter in the colon and a reservoir of fluid in the bladder does also give us freedom to release when it is safe to do so, which may protect us from predators (having to stop to poop even a few times a day is dangerous compared to only going when you know it's safe to as there are more opportunities to be attacked by a predator). It would also be very easy to track an animal that leaves a constant trail of poop and urine uncontrollably behind it.

All or none of these may be reasons why we have separate urinary and alimentary tracts; it's impossible to know and would always be speculation. But regardless these do seem like reasonable reasons why we may have separate tracts.

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Drewdp@lemmy.world ⁨1⁩ ⁨year⁩ ago
The kidneys already recover water and salt. Google the loop of Henley.

What we pee is what our body considers in excess. We intake a lot of our water from food, so we need a way to expel that. Peeing is much nicer than bloating and constant Diarra.

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- Thurkeau@lemmy.world ⁨1⁩ ⁨year⁩ ago
  True, though as is, we still need to take in water due to a shortfall in what we do take in. That said, I’m also wondering if my proposal would also result in other waste products being recirculated and building up in the system, causing their own complications.
  
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  - Zeth0s@lemmy.world ⁨1⁩ ⁨year⁩ ago
    You are asking for kidney stones. There’s a chemical reason you want plenty of water to dilute your waste, that is precipitation
    
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  - match@pawb.social ⁨1⁩ ⁨year⁩ ago
    One waste product building up would be water, in that case
    
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jaanus20@lemm.ee ⁨1⁩ ⁨year⁩ ago
Not a biologist, just a normal dude. Isn’t one function of urine to flush out toxins? With them staying in the intestines could it poison the human?

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- Thurkeau@lemmy.world ⁨1⁩ ⁨year⁩ ago
  That’s actually part of my question. The bowels also dump toxins overboard as well, but will they be enough to do the job?
  
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  - aubertlone@lemmy.world ⁨1⁩ ⁨year⁩ ago
    I think you need to perhaps watch some videos explaining the anatomy/physiology of the gastrointestinal tract and urinary tract.
    
    The kind of questions you’re asking can be easily answered with an understanding of the systems I’ve stated above.
    
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I_Clean_Here@lemmy.world ⁨1⁩ ⁨year⁩ ago
What if my mother had wheels?

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rufus@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
You’re looking for a Cloaka

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- Thurkeau@lemmy.world ⁨1⁩ ⁨year⁩ ago
  A cloaca still has facilities for urine to be dumped overboard, doesn’t it? My proposal is to recirculate it before dumping it overboard dry.
  
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  - rufus@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
    And what would you do with the water you’ve taken out in the drying process?
    
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angrystego@lemmy.world ⁨1⁩ ⁨year⁩ ago
The other solution would be to evolve a bladder capable of reabsorbing water.

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- Thurkeau@lemmy.world ⁨1⁩ ⁨year⁩ ago
  That is also something that I have wondered about, but that probably isn’t a thing because of salt buildup.
  
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sagrotan@lemmy.world ⁨1⁩ ⁨year⁩ ago
The beargryllneys?

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