Hello All,

        I am not in the medical field but I do have a litte
knowledge of molecular biology, and a strong knowledge in
electrical engineer.  I am starting to recognize that body
is one of the most efficient system known to man.  However,
I would like to know:

1) Why the body thrist for water???
2) Why is water satisfy your thrist when orange juice can not??
3) What is going on within the brain, throat area, and cells???
4) What is a fundamental book, or journals can a novice read
    in this area???

                                        Thanks in advance

Jonathan B. Walker :

Odd.
I have the reverse.  In summer (but not after exercise in winter)
incipient dehydration causes a desire for an acidic drink, e.g.
orange juice, tea with lemon, (or even water with a dash of vinegar !)
that is not satisfied by plain water.

--

    Because your internal fluid has become (slightly) hypertonic (higher
concentration of solutes, lower relative concentration of water).

    Because water has _no_ solutes, but OJ has some. I'd think OJ would
still do the job, just not as quickly.

    There are some cells in the hypothalamus which are very sensitive to
hypertonic conditions. In hypertonic conditions, they send signals to (among
other things) cause the kidney to concentrate the urine (thus effectively
reducing the tonicity of body fluids by expelling a _very_ hypertonic urine)
and to give the sensation of thirst (including a dry throat).

    Sorry, I'm not sure...                                      -J

________________________________________________________________________________

        Class of 1997, Columbia University P&S (a.k.a. Columbia Med)

       If I say anything incomprehensible, translations to usable English
              are provided by e-mail...       Free of charge! ;-)

                I believe in courtesy copies of posts by e-mail                

CURRENT IMPORTANCE OF FLUID BALANCES AND HYDRATION:
CLINICAL OUTCOMES IN THE ELDERLY

Dear colleagues and interested others:

An excellent and reasonably current article I came across in journal
review, besides standard medical texts on fluid and electrolyte balances,
is  

Warren, JL, et al., The burdens and outcomes associated with dehydration
among US elderly, 1991, AM J PUBLIC HEALTH. 1994:84:1265-1269

"The hospitalization of elderly people with dehydration is a serious and
costly medical problem.  Attention should be directed on understanding
predisposing factors and devising strategies for prevention" .  While this
article is very comprehensive, it only FOCUSES ON CLINICAL OUTCOME FROM
DEHYDRATION RATHER THAN WHY IT EXISTS. Brain feedback mechanisms are not
discussed.  The main thrust is that we should ".........educate elderly
patients, especially those living alone, regarding the risk of dehydration
and the need to maintain adequate {*filter*}intake during periods of acute
illness." Dehydration is "......a significant cause of mortality, morbidity
and health care costs of the elderly."  

Only a very comprehensive "patient-centered" assessment with appropriate
physical examination of the patient as well as lab studies can determine
the reason for dehydration in any given patient. From a purely clinical
ecology and toxicology view, "the solution to pollution is dilution" which
is done with water.  This is very important in operating detox systems such
as cytochrome P-450 and glutathione=S-transferase systems.  Indeed, basic
metabolism cannot exist without water.  There are so many aspects and
variability to it that the clinician must look at PATIENT-SPECIFIC REASONS
FOR THE DEVELOPMENT OF DEHYDRATION IN THIS PARTICULAR PATIENT AT THIS
PARTICULAR TIME. DOES THIS CORRELATE WITH ANY OTHER SYMPTOMS OF THE
PATIENT? (1)  WHAT TRIGGERED IT, (2) WHAT UNDERLYING METABOLIC PATHWAYS
MEDIATED ITS DEVELOPMENT (3) AND WHAT ANTECEDENTS IN THE LIFE OF THIS
PATIENT DETERMINED THE EVOLUTION OF THIS SYMPTOM [COMPLEX]?

Sincerely,  

(718) 460-3966, American Academy of Anti-Aging Medicine, International
Association of Biomedical Gerontology, American Aging Association, National
Academy of Elder Law Attorneys, Life Extension  Foundation, American
Academy of Clinical Gerontology, Certified: Mediation & Counseling,
Certified: Functional Assessments & Intervention, Art 81 NY MHL,
Certification Pending: Interdisciplinary Geriatrics, Columbia
University--NY Geriatric Education Center

: Hello All,
:
:  I am not in the medical field but I do have a litte
Nor I, but interested.
: knowledge of molecular biology, and a strong knowledge in
: electrical engineer.  I am starting to recognize that body
: is one of the most efficient system known to man.  However,
: I would like to know:
:  
: 1) Why the body thrist for water???

Can be diabetes, also note people who restrict salt sometimes drink more - I
suppose as salt level goes down the body loses water to keep the {*filter*}
salinity correct, then something else says there is not enough water in the
body.

: 2) Why is water satisfy your thrist when orange juice can not??

If your pH is too low or high, say from vinegar, or even acid fruit, water
helps.

: 3) What is going on within the brain, throat area, and cells???
: 4) What is a fundamental book, or journals can a novice read
:     in this area???

Davidson and Passmore, "Human Nutrition and Dietetics" has quite a bit,
including water intoxication.
:
:      Thanks in advance
:

:

Hmmm. So this must be why drinking sea water is a bad idea: the salts just
make you thirstier. I've heard conflicting opinions on this though: does
drinking sea water just make you _feel_ thirstier, or does it really not do
anything for your dehydration? --I just want to know in case I'm ever cast
adrift at sea.

--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
             |      Die Welt ist alles, was Zerfall ist.     |

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[snip}

    Just for your information: drinking sea water for thirst is BAD (big
time) since, in addition to not helping your osmotic situation, is will also
make you sick to your stomach. Of course, thinking about it, I'm wondering
if your kidneys might be able to rev-up enough to shed the salt you
consume...  if it could get rid of enough salt, you might be able to get by.
Of course, I think that reaches the range where you'd need the kidneys of a
gerbil to handle it. -J

________________________________________________________________________________

        Class of 1997, Columbia University P&S (a.k.a. Columbia Med)

       If I say anything incomprehensible, translations to usable English
              are provided by e-mail...       Free of charge! ;-)

                I believe in courtesy copies of posts by e-mail                

All these things are relative, of course.  Sea water is not uniform in
concentration.  Some species have better kidneys than others.  
Schmidt-Nielsen and Schmidt-Nielsen did a study in the 50's to see if
kangaroo rats could survive on seawater, or more properly, on salty water
the approximate concentration of seawater.  K-rats are hard desert
adapted, and, it turned out, drank no water at all when maintained on
pearled barley.  They got all the water they needed from metabolism of
the carbohydrate.  When they added protein to the diet to increase the
obligatory excretion of urine (ammonia), they found the k-rats did just
fine on seawater.  Hamsters are also desert adapted, but not adept enough
to survive without some free water intake.  Rats even less so.

By the way, a contributor to the thirst other than osmoreceptors already
mentioned is angiotensin II.  This contributes to thirst during
*extra*cellular dehydration.

Doug Fitts