thick blood, the bladder, and dehydration

i work canvassing homes door to door for a good part of the day. start off the day with at least one cup of coffee. and since the weather has been so hot, i’ve been drinking a lot of water while out on foot. being out on foot, i also don’t have the use of ‘facilities’ all too often.

and it’s gotten me thinking, when my bladder’s full, and i’ve been sweating a lot under a broiling “Why the hell didn’t we sign the Kyoto Accord” sun, and i’m dehydrated as a result, can my body reabsorb needed water from the big supply down below?

in other words, can a man’s bladder act like the hump of his Joe Camel?


Seems your body takes care of most of the reabsorption anyway. The kidneys produce 180 litres of urine, with only 1.5 to 2 litres excreted daily.

From this site. When your water intake is down, the body automatically compensates by adjusting the contration of your urine.

To answer the OP:

No. Once the urine has left the kidneys there’s no going back.

okay. i’ve been doing some more digging about kidneys.

this site in particular fascinated me:

anyway, this research has gotten me thinking, and i can’t seem to find any nonlingoriffic sources of information on a particular question.

about how long after drinking water does the water get into the bladder? i’m guessing that would be hard to pinpoint, because water absorption gets all complicated in the stomach and large and small intestines. and also because the water you drink dilutes your blood, and the kidneys filter the water out of your blood, so (some of) the water you drink could conceivably go into your kidneys right away, or could get recirculated in the blood for ages.

and finally, am i right in guessing that urine is nothing more than a certain concentrate of blood? that is, do the kidneys do any metabolization, or only simple (!) concentration?


To answer your “length of time” question: It depends on so many variables that it’s hard to give a meaningful answer. Anywhere from minutes to a couple of days are possible, given certain conditions.

And secondly, urine is an untra-filtrate of blood, with certain blood substances concentrated (such as urea) and certain blood substances diluted (such as sodium).

**JB,[/] nothing the kidneys do is simple. As Qadgop indicated, the kidneys concentrate some substances and dilute others, relative to the blood. What’s really fascinating, though, is that the degree to which a compound is resorbed by the kidney is under dynamic control. If, as in your example, you take in a large amount of water, the kidneys can let water pour right through them (and without losing much else), restoring your inner homeostasis.

In answer to you first question about how long does water take to make the trip, I agree with Qag that the time would vary, but perhaps we can come closer to pinning down a number. If you empty your bladder then drink 2 quarts of water, how long before you need to pee again? For me, I’d say between 30-60 minutes. Remember, that’s how long it took the 300 ml bladder to fill, so water got from the GI tract to the kidneys much faster. My WAG is that the first water molecules excreted woud be there by 3-5 minutes.