vallmo
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Plasma (Na) = 135 (normal=135-147)
Serum glukos = 100 (70-110)
Serum urea= 100 (7-18)
Posm ´=310 (280-295)
Would plasma ADH levels be individual be elevated or suppressed?
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| vrach
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elevated (stimulation of hypothalamic osmo receptors)
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| vallmo
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No, it would decrease. The books answer:
although the plasma osmolality is elevated, the increased osmol is caused by urea. Because urea is an ineffective osmole with regard to ADH secretion, it is necessary to estimate the osmolality of plasma that is attributet to effective osmoles (Na+ and its anions) the effective osmolality of the plasma is estimated by doubling the plasma 8Na+), which yields a value of 270 mOsm/kg H2O.
Because the effective osmolality is reduced from its normal value (280 to 290 mOsm/kgH2O), ADH secretion is suppressed and plasma levels reduced.
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| mjl1717
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With this renal physio that we do I will answer quite meticulously. I find this part a real battle:
Increases ADH secretion:
increase serum osmolarity
volume contraction
pain, *nausea
hypoglycemia
nicotine
opiates, antineoplastic drugs
Decreases ADH secretion
decrease serum osmolarity
ethanol
alpha agonist
ANF
comments welcome
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| mjl1717
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As we can see even with this straight forward q -there is controversy.
By the way where is Mani?? {Need every viable soldier we can get for this renal warefare.
This book by Vander stated the major controls for ADH are:
1)As stated body fluid osmolarity via hypothalamic osmoreceptors
2)plasma vol. (specifically left atrial baroreceptors.)
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| mjl1717
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Good-I think I get your point Vallmo since **urea is about 50% reabsorbed-I think it makes sense.
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| vrach
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Nice q Vallmo, and thanks for the explination and sharing it. It seemed like such a simple straight forward Q :|
I'll make it a point from now on to calculate the effective osmollarity for any solution that has urea in it....
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| sr
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can someone please explain why urea is an ineffective osmole? my prof said this in class, but never bothered to explain it. he just told us to know.
is it because adh is secreted with high serum osmolarity, which causes water AND urea to be reabsorbed. thus, if urea were an effective osmole, then this would be counter-intuitive. so it must be an ineffective osmole in terms of adh release. yes or no???
thanks in advance.
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