sweating

[Daave]

how come you can be dehydrated in the summer and sweat loads, but you still need a wee? why doest the body make the liquids go to the other places instead of making wee? and once in your bladder, can the liquid come back out and go back into different parts of the body, or is it a "one way system"

[theprof]

First of all, when you say you�re dehydrated in summer, you�re not really dehydrated in the medical sense even though you feel you�re desperately in need of hydration. You can survive in most temperate climates for a matter of days on the fluid in your circulation as around 53% of the body is made up of water anyway.

Medical mild dehydration has symptoms such as extreme thirst or inability to drink, cramps, lethargy, inability to pass urine or very reduced dark urine output and sleepiness. Severe dehydration symptoms include convulsions, cardiac failure, muscle spasms and twitches and a very weak pulse and shock.

A healthy adult disposes of between 1.5 and 2.5 litres of urine a day. It varies because firstly, water input varies and secondly, output via respiration can change during the day. There are some other reasons as well apart from sweating but I won�t complicate matters.

The body contains a finely balanced quantity of electrolytes such as bicarbonate, sodium, magnesium and potassium. These electrolytes are needed for complex metabolic interactions by the body and its important that the correct levels are maintained at all times. Cells and blood vessels could burst without the correct quantities in the body and other serious consequences would occur too such as damage to nerves.

(continued)

[theprof]

Excess fluid (water) in the circulation causes dilution of these electrolytes and this would have serious consequences for the body. It�s instinctive to drink more fluid in hot weather, but to prevent harm arising, the body has to dispose of this excess fluid. The body also produces somewhere in the region of 450-550 ml of fluid daily just to dispose of toxic waste products that are produced as a result of metabolism and to maintain a state of equilibrium in the body (homeostasis).

All the fluid necessary to maintain this balance does go to the parts of the body where its needed � urine is produced when there�s an excess.

Under normal circumstances, fluid is not reabsorbed from the bladder in humans although it can occur in some unusual circumstances. The kidneys do the reabsorbtion in humans.

Oddly enough, frogs have the capacity to absorb fluids from the bladder routinely due to their unique physiology.

[Finance Guy]

that was the most amazing answer i think i have ever seen!

[neuron]

You think so Finance Guy? You should see some of the other answers theprof has given in Science on AB. Just type theprof into the search box and see for yourself.

He's received more praise for explaining things on AB than any other poster I've seen. Personally, I think he was in a terse mood yesterday afternoon!

What do you say Prof?

[theprof]

I'm blushing.