immersion diuresis and temperature

[dozeydo]

Just a further thought that came to me in the bath(!) today - does the temperature of the water have any effect on this phenomenom? I am thinking of the effects of vasodilation/vasoconstriction on the amount of blood that passes through the extremities - would cold water increase the effect/ Also, is that why, when the weather is cold, we need to pee more?

[Hippy]

Cold makes the blood vessels in your extremeties narrow so as to conserve heat to the vital organs in your body. When you are in nice warm water in the bath or Jacuzzi you relax and the blood vessels open up and your heart rate decreases and eventually your blood pressure drops and you are in a beautifully relaxed warm and safe state.

Stand up quickly and you get faint as the blood pressure is too low to maintain enough oxygen to your brain. This situation will quickly right itself, but the moment of blurr or even unconsciousness has caused many people to fall over and hurt themmselves.

Immerse yourself in cold water and the opposite happens. Your body tries to conserve heat and stops your limbs from acting as radiators and loosing it. The warmth is conserverd to your trunk and head. Your heart rate and blood pressure alter to accommodate this new flow pattern.

I've often wondered about peeing in cold weather, and thought that surely this expells heat from the body, but I suppose it is a method of regulating fluids in the body. Urine serves no purpose in keeping the body warm, it does not circulate, and with the increased flow of blood around the central organs more urine is likely to be produced than normal. The bladder will feel full even when it is not causing the peeing trigger at a much earlier stage. We probably do not pee more but pee more often.

[dozeydo]

Thanks, Hippy, but if in cold water/air, when the blood vessels near the surface of the skin constrict to prevent heat loss, there is more blood directed to the body core - this should therefore cause a drop in the production of ADH as the core would appear to have too much fluid and hence the production of more urine - am I correct? this is what I wanted to know.

[theprof]

Apologies for jumping in dozeydo, but I recently answered a similar question to the issues you raised in your last post here:

http://www.theanswerbank.co.uk/Science/Questio n330486.html

I realise the question I answered did not take account of the water temperature, so if my answer doesn't help, let me know and I'll try to explain further.

I take it you meant to say "hence increase the production of more urine..." in your post?

[dozeydo]

Thanks, Prof - this was just a thought that came to me after reading your previous post. I was hoping you'd get involved. Yes, I did mean to say increase the production ... . Really, my original question was not as clear as it might have been due to a grandchild bouncing on my knee and somewhat impeding my train of thought! Do you think that the volume of urine is increased if the immersion is in cold water as opposed to that produced if the immersion is in water at around body temp? I was thinking that there would be two effects - the diuresis from the effect of pressure and that produced by the vasoconstriction - two effects= production of more urine??

[theprof]

Yes, you�re absolutely right to think that the volume of urine produced following immersion in cold water is greater than that produced when the body is immersed in water at near body temperature.

The first thing that happens following immersion in cold water is that vasoconstriction occurs. This in turn, causes blood to be directed away from the skin surface of the body to deeper blood vessels, mainly veins. Veins can carry this increased volume of blood because they have the ability to stretch to relatively huge diameters.

Now, when all the blood vessels in the body carry the optimum quantity of blood, the heart maintains a fairly steady input-output rate. However, when the blood circulates in mainly core blood vessels, as it does during vasoconstriction, there is an increase in the venous blood return to the heart.

This increased venous blood return causes the atria in the chambers of the heart to enlarge or distend. These atria contain special cells that release a hormone called Atrial Natruretic Factor (ANF) that increases diuresis. Also, nerve receptors in the atria send a signal to the brain to decrease the production of ADH, resulting in further increased urine production.

(continued)

[theprof]

When I was diving myself many years ago when I was a student, we were taught that diving in cold water caused the blood vessels in our limbs to constrict in order to avoid loss of body heat. The blood in the thoracic cavity then increased and this in turn increased the volume of blood to the atria of the heart. Diving in warm water causes the body to respond in the opposite manner. This was a pretty good summary of what happens.

As far as pressure goes, it doesn�t play a big part in diuresis, at least not as far as diving is concerned. From personal experience, I�ve been on shallow and deep dives and can�t really say I�ve felt the urge to pee on one more than the other, after taking time underwater into account. If the water is cold, diuresis occurs anyway. It�s no good asking divers because most of them deny they ever pee in the water anyway, and there is a bit of an art in peeing during dives which depends on your diving gear!

One other thing that comes to mind over this is that much research has shown that the age of the person plays a part. The older you are, the greater the diuresis and the greater the frequency of peeing.

Let me know if I can help anymore.

[dozeydo]

Prof, you are a star! Thank you so much! I'm not a biologist, just a humble chem teacher and Ididn't know of the existence of ANF - the way the body works to maintain equilibria is fascinating. Once again, many thanks.

[theprof]

Thanks dozeydo.

Humble chemistry teacher eh? Don't knock it - I was once a chemistry lecturer myself!

Although I'm now a Professor of Biochemistry and a university Dean , I' ve got assorted degrees up to and including Scd's in chemistry, biology and biochemistry as well as the usual fellowships.

Once again this year, my daughter gave my grandaughters a pencil and paper and asked them to work out which letters of the alphabet grandad didn't have after his name. As usual, it caused much hilarity amongst the family, but it just pis*es me off!