Re: Sodium homeostasis... was Re: tears

Thomas Clarke (
2 Nov 1995 13:23:02 GMT

In article <> (J. Moore) writes:

>AD> >salt proportion of the body a "salt-excretion mechanism" if you wish.
>AD> >It doesn't change the fact that tears are not an effective
>AD> >mechanism for ridding the body of excess salt.

>IB> Anything that gets rid of salt can be a salt excretion mechanism. I
>IB> agree that unless they wept a lot it would be ineffective, certainly
>IB> not as effective as kidneys or sweating but so what.

>The problem for the body, in terms of excreting of sodium (or
>potassium, etc.), is maintaining a balance (homeostasis) of water
>and sodium (or potassium, etc.). If an excreted solution has the
>same ratio of sodium to water as is in plasma, it doesn't change
>this balance, and the organ excreting this solution is not going
>to be able to rid the body of excess sodium. The solution itself
>is said to be isotonic. This is the situation with human tears.

That is only true if you drink fluid that has the same ratio of
sodium to water as plasma, e.g. Gatorade(tm). If you drink
water your salt content goes down, your water content stays the
same. You loose salt.

>Human sweating excretes a substance which is hypotonic, having a
>lower ratio of sodium to water than is in plasma. Here too, the
>solution is not useful at ridding the body of excess sodium --
>quite the opposite -- since the body is eliminating proportionately
>more water than sodium from its plasma as it sweats.

I heard the inventor of Gatorade(tm) Dr. McCade talk once. I
don't remember him saying whether Gatorade compared to tears
or sweat or to plasma in its salt content. He said that he
was moved to invent (discover?) Gatorade when a friend of his
remarked that you never peed during a football game if you were
a player. This interested Dr, McCade the urologist and he got
some freshmen players to let him take blood before and after
practice. He was amazed, if the players had showed up in an
emergency room after practice, their blood electrolytes were
so out of balance that they would have immediately have been
put on an IV. So McCade mixed some salt and glucose and some
lemon to make it palatable and fed it to the same frosh volunteers.
WHen the frosh beat the upperclass second team, the coach took
notice and then the varsity used Dr. McCade's magic drink
(kind of like Fred MacMurray) and for a couple of years the
Univ of FLorida "Gators" had a "magic" weapon. The rest is history.

Sweating certainly does remove salt from the body.

>Mammalian urine, on the other hand, is hypertonic, having a higher
>ratio of sodium to water than is in plasma. It is therefore
>effective in getting rid of excess sodium from the body's plasma.

Oh even better. In the above story you don't need to pee if
you are sweating profusely.

Come to think of it, on a hot summer day when I am working in
the garage sweating I drink a lot of water, but I don't have
to run inside to the bathroom much. Actually its not water,
but iced tea which is allegedly diuretic.

This has probably nothing to do with homind evolution, but sweating does
eliminate salt. Not enough to allow you to drink seawater but
enough to make you sick if you don't replace it.

Tom Clarke