Dehydration

[237SJ]

It seems to be a recognised fact that if somebody is starving, their body goes into `starvation mode` and slows down their metabolism. If a body is in a very dry situation therefore, does the human body conserve liquids and try to hold on to the fluids in the body? Would that theory explain why I "pee for Africa" when I get off a long haul flight?

[Buenchico]

It's more likely to be because of the increase in ambient pressure.

Although aircraft cabins are pressurised it's not to the same level as on the ground. That's why your feet can swell. Similarly, while on the plane, your bladder isn't squeezed by atmospheric pressure in the same way that it is when you leave the aircraft.

So you tend not to notice the build up of fluids in your bladder while on the flight (because your bladder is slack due to the low pressure) but you suddenly realise that you're 'busting for a pee' when your bladder tightens up under normal atmospheric pressure.

Chris

[Sqad]

I am not a physiologist so take my answer as you will.

Cabins are pressurised to about the equivalent to 8,000feet and this results in breathing in 25%less oxygen

Also the humidity in cabins is low and the body, as you quite rightly say, tends to retain fluid by reducing the rate that you produce urine and also by reducing fluid lost by the skin.

If you drink plenty on the plane to combat dehydration,the kidney´s return to normal urine production is delayed until after the flight, when they again "kick in" and secrete urine normally.

Also throughout the flight your O2 levels are lower than normal which again restricts urine formation and again when this returns to normal after the flight you "pee for Africa"

In my opinion the effect of atmospheric pressure on the bladder is minimal as the bladder is protected by strong abdominal muscles.

I look forward to more informed comments.

[237SJ]

Thanks for your answers.
Sqad, that`s very interesting. I didn`t know reduced O2 levels restricted urine formation. That explains why, when I was on weightwatchers I was always heavier just after a flight. It was all that liquid waiting to be expelled.