filtrate osmolarity - kidney. please help

[sacha]

EK bio states that the 'net effect of the distal tubule is to lower filtrate osmolarity' it also states that 'in the presence of ADH, water flows from the tubule concentrating the urine'. doesn't this increase filtrate osmolarity since osmolarity measures solute concentration? i feel like the two facts are contradicting each other? am i wrong? (for those with ek bio its in the first paragraph of pg 135) help! 🙂

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[sacha]

EK bio states that the 'net effect of the distal tubule is to lower filtrate osmolarity' it also states that 'in the presence of ADH, water flows from the tubule concentrating the urine'. doesn't this increase filtrate osmolarity since osmolarity measures solute concentration? i feel like the two facts are contradicting each other? am i wrong? (for those with ek bio its in the first paragraph of pg 135) help! 🙂

ahh. problem solved. apparently only the end of distal tubule is sensitive to ADH. so generally, it does lower filtrate osmolarity.

 

[xlcooplx]

ahh. problem solved. apparently only the end of distal tubule is sensitive to ADH. so generally, it does lower filtrate osmolarity.

That would be correct. I just read this same chapter earlier today. I actually ready the kidney/nephron part twice in order to try and grasp it but I still couldn't fully conceptualize it. I found this video on youtube earlier and it really helped me to understand why the Loop of Henle functions as it does.

http://www.youtube.com/watch?v=cc8sUv2SuaY

 

[ilovemcat]

EK bio states that the 'net effect of the distal tubule is to lower filtrate osmolarity' it also states that 'in the presence of ADH, water flows from the tubule concentrating the urine'. doesn't this increase filtrate osmolarity since osmolarity measures solute concentration? i feel like the two facts are contradicting each other? am i wrong? (for those with ek bio its in the first paragraph of pg 135) help! 🙂

ahh. problem solved. apparently only the end of distal tubule is sensitive to ADH. so generally, it does lower filtrate osmolarity.

That's a little strange they would say that, because even in the absence of ADH and Aldosterone, while sodium and chloride are being reabsorbed into the interstitium, potassium and hydrogen ions are being secreted into the Distal CT. It would seem both of these changes negate any change in filtrate osmolarity. I'm having a hard time understanding why filtrate osmolarity would decrease in the first place. Even in the diagram it shows that osmolarity doesn't charge (it stays steady at 100).

However, I do understand that if ADH (promotes water reabsorption) and Aldosterone (promotes sodium uptake and water reabsorption indirectly) were present, there would be an increase filtrate osmolarity.

By the way, what page did you see that on?