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peridot
Great explanation, thank you so much!!
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frijoles
So potassium does not become diluted in SIADH?
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ruready4this
I feel like I was overthinking this question so much for some reason!! C definitely makes the most sense but I was also wondering what would happen to potassium. Then I was thinking maybe the excess ADH would suppress aldosterone secretion and serum potassium concentration would actually be higher
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peridot
@frijoles Aldosterone can adjust the K+ levels: too much water --> less aldosterone --> no excretion of K+, so this helps retain the K+ to a normal level. However, less aldosterone also means --> more excretion of Na+, so the hyponatremia is not corrected.
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submitted by โandro(269)
SIADH is characterized by :
*Excessive free water retention ( less water in urine means specific gravity increases and not decreases as in option E)
*Euvolemic hyponatremia with continued urinary Na+ excretion ( and so urine Na which actually be greater than and not less than 10 mEq/L option D)
*Urine osmolality > serum osmolality ( option C)
Serum potassium does not actually decrease ( counter-intuitively ) because the excess fluid retention suppresses aldosterone secretion . The two main stimuli for potassium loss/secretion in kidneys are - aldosterone - and high urine flow rates. Both of these are decreased in SIADH ( excluding option B )
Serum urea nitrogen and creatinine are diluted , so their concentration decreases