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Old 08-17-2015
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Default question about Goljan fluid/hemodynamics

My question is why do you give DI (diabetes inspidus) patients pure water? They are losing pure water? Can somebody explain the pathophysiology? Thank you

Last edited by pocket; 08-17-2015 at 09:10 AM.
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Old 08-17-2015
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In diabetes insipidus, FREE water cannot be reabsorbed in collecting tubules.
You see, in proximal tubule, there is some water reabsorption that is BOUND to Na+ -sodium is reabsorbed and takes water with it.
In collecting tubule you have these channels called aquaporins that allow reabsorption of free water. In this case it does not follow sodium. Medulla is more hypertonic the deeper you go. Therefore, as collecting duct goes deeper and deeper, water can still be reabsorbed. This is important in dehydration - your kidneys saveas much water as they can. For the aquaporins to be inserted into luminal membrane, ADH must bind V2 receptors. If either one of them is missing, you cannot reabsorb this water and eventually, you get dehydration. This can be compensated by drinking water.
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