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Medullary segment of thick ascending limb - where the Na/K-2Cl pump is - which is where loop diuretics block. The Na/K-2Cl pump generates free water. The two type of water in urine: obligated and free. If the water is obligated, then the water is obligated to go out with every Na, K, and Cl (concentrated urea). Basically 20 ml's of obligated water for every Na, K, Cl (it's obligated) via Na/K/2Cl pump. The ADH hormone absorbs free water b/c the pump generates free water.
Let's say you absorb one Na, how much free water is left behind in the urine? - 20 mls; then reabsorbed another K, that is another 20, so its up to 40; another 2 Cl's are reabsorbed which is another 40; therefore, for absorbing one Na, one K, and 2 Cl's, you have taken 80 mls of free water from the urine - this is free water that is generated; its is this pump that loop diuretics block, which is in the thick ascending limb of the medullary segment.

this is what said told in goljan audio....but cant understand..if na-k-2 cl cotransport causes 80 ml of free water absorbed..but also said that ""
If the water is obligated, then the water is obligated to go out with every Na, K, and Cl (concentrated urea). Basically 20 ml's of obligated water for every Na, K, Cl (it's obligated) via Na/K/2Cl pump""
so whats true--na/k/2 cl cotranport associated with free water or obligated water..


 

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ascending portion is impermeable to water so free water is produced not reabsorbed. If u block it with a loop then you're not producing that free water which could've been reabsorbed in the collecting ducts via ADH, hence diuresis occurs.
 

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free water...free from obligation

free water is generated from the water-impermeable medullary (Na/K/2cl) and cortical (Na/Cl) portions of the nephron.
20ml of water is obliged to be excreted with each Na etc.
But because of the action of these 2 pumps, Na, K ,Cl are absorbed , hence freeing that water from its obligation, i.e converts obligated water to free water, which can the be reabsorbed via ADH dependent mechanisms in the collecting tubule and duct.
Blocking these pumps, reduces free water, and increases obligated water which is passed out as diuresis.
 

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free water is generated from the water-impermeable medullary (Na/K/2cl) and cortical (Na/Cl) portions of the nephron.
20ml of water is obliged to be excreted with each Na etc.
But because of the action of these 2 pumps, Na, K ,Cl are absorbed , hence freeing that water from its obligation, i.e converts obligated water to free water, which can the be reabsorbed via ADH dependent mechanisms in the collecting tubule and duct.
Blocking these pumps, reduces free water, and increases obligated water which is passed out as diuresis.
blocking ADH pumps would increase free water not reduce.
 

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The Na/K-2Cl pump generates free water. the ascending limb is the diluting segment . Salt is extracted and a hypotonic fluid is left in the lumen which will pass thru unaffected . ADH makes the wall of the remaining portion of DCT and CD permeable to water , ensuring we absorb "free" water , without any Na , K ,Cl ,tied to it . The pump dissociates water movement with Ion movement .

The two type of water in urine: obligated and free. If the water is obligated, then the water is obligated to go out with every Na, K, and Cl (concentrated urea). Basically 20 ml’s of obligated water for every Na, K, Cl (it’s obligated) via Na/K/2Cl pump. The ADH hormone absorbs free water b/c the pump generates free water.

Let’s say you absorb one Na, how much free water is left behind in the urine? – 20 mls; then reabsorbed another K, that is another 20, so its up to 40; another 2 Cl’s are reabsorbed which is another 40; therefore, for absorbing one Na, one K, and 2 Cl’s, you have taken 80 mls of free water from the urine – this is free water that is generated;


it is this pump that loop diuretics block, which is in the thick ascending limb of the medullary segment. So the ions remain in the lumen , binding the water with them , prevent absorption via ADH mediated increase in permeability and thus cause diuresis
 
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