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Re: AAT Questions...
Gerrit Hanenburg (ghanenbu@inter.nl.net)
Thu, 17 Aug 1995 11:31:44 GMT
Elaine Morgan <Elaine@desco.demon.co.uk> wrote:
>Gerrit: Good points about the urine. It would seem to stand to reason
>that if anything had kidneys they would cope with excess salinity.
>But in practice it doesn't always apply. The marine cvreatures that use
>salt glands or lacrimal glands have kidneys too. Maybe if they get too
>overloadd with salt it would impair thair capacity to deal with other
>toxic wastes. Our urine by the way is at the dilute end of the
>spectrum, for what that's worth - all part of general pattern of
>leakiness...
Nevertheless the maximum concentration in urine is almost 5 times that of
plasma.(1400 mosmol/l against 290 mosmol/l).So urine can be hypertonic.
The concentration of salt in eccrine sweat is 0.1% (compared to 0.9% in
plasma).Sweat is hypotonic and never hypertonic.Most of the salt in primary
sweat (isotonic) is reabsorbed on the way out.Not something I would expect
from an aquatic ape heritage.
You assume that sweat was once hypertonic.This would mean excretion of salt
against a gradient (low -> high).In biological systems this can only be done
by active transport (requiring energy).As far as I know there is not a trace
of a "scar" of such inside -> outside transport in the human eccrine sweat
gland.
The eccrine sweat gland seems to be adapted to keeping as much salt inside as
possible (but,as so often,this adaptation is not perfect and seems to settle
with almost 90% reabsorption instead of 100%)
Gerrit.
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