osmosis in a lake?

[hbhobby]

I never though about it untill yesterday doing some diving. but my question is when diving fresh water do you absorb water through osmosis into your body? the reason I ask is when diving yesterday I had to urinate about 5 times in a 3 hour period (no wetsuit ) and I am usually the type of guy that only has to urinate 5 times a day. so I was curious as to where all this extra water was coming from. and if it is correct that you gain water in fresh water do you actually lose water in salt water diving? just though I would ask some of the more experianced folks out there

 

[lowviz]

Another explanation can be found in Public Safety Diving by Butch Hendrick, Andrea Zaferes, and Craig Nelson around page 202:

The general idea is that cold causes the body to shunt blood from the extremities to the core in order to conserve heat. The increased blood pressure in the core is somewhat countered by the kidneys removing extra water. -same effect with exposure to the ocean or cold air.

-stay hydrated, wear your wetsuit

 

[TSandM]

There is some absorption of water in fresh water (which is why your fingers get wrinkly in the bathtub) but in terms of overall body volume, it's negligible. The reason for the increased urination is a phenomenon called immersion diuresis.

 

[tridacna]

I never though about it untill yesterday doing some diving. but my question is when diving fresh water do you absorb water through osmosis into your body? the reason I ask is when diving yesterday I had to urinate about 5 times in a 3 hour period (no wetsuit ) and I am usually the type of guy that only has to urinate 5 times a day. so I was curious as to where all this extra water was coming from. and if it is correct that you gain water in fresh water do you actually lose water in salt water diving? just though I would ask some of the more experianced folks out there

Untrue. Osmosis is the transport of water across a semi-permeable membrane, which always flows across the membrane from the lower salt concentration to the higher salt concentration. Fresh water has a much lower salt concentration than your body so your process of water loss cannot be explained via osmosis. In salt water, simple diffusion would occur and your skin will get tight due to the water in your dead cells diffusing into the salty water (via simple diffusion, not osmosis). You will not lose water.

 

[lowviz]

There is some absorption of water in fresh water (which is why your fingers get wrinkly in the bathtub) but in terms of overall body volume, it's negligible. The reason for the increased urination is a phenomenon called immersion diuresis.

-a better description. Which leads to the next question: Is blood volume sensed differently than blood pressure?

 

[dmoore19]

There is some absorption of water in fresh water (which is why your fingers get wrinkly in the bathtub) but in terms of overall body volume, it's negligible. The reason for the increased urination is a phenomenon called immersion diuresis.

WOW, the things you can learn while clicking around on scuaboard. Thanks for the information.

With this in mind, it may be important to hydrate before diving but it seems to me that maybe more important would be to make sure you hydrate during SIs and after a day of diving especially!

 

[Doc Harry]

Which leads to the next question: Is blood volume sensed differently than blood pressure?

Yes and no. Maybe. Clear?

There are no volume sensors, per se. The body does monitor osmotic pressure, which can be thought of as "volume" sensor. Expansion of intravascular volume decreases osmotic pressure, whereas contraction of intravascular volume increases osmotic pressure.

There are baroreceptors that monitor vascular pressure directly.

In the case of immersion diuresis, it is both osmoreceptors and baroreceptors that cause the diuresis.

Generally, the body operates on the assumption that the pressure/volume relationship is somewhat linear. When that linearity breaks down, so does the body's ability to cope properly. Examples of such breakdown includes congestive heart failure, hypertension and intercranial bleeds. In these diseases, the body's attempts to correct the problem may be inappropriate and may actually try to correct in the wrong direction.