Nephron question?

[fas376]

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In the descending limb of the loop of Henle, water exits. In the ascending limb, sodium and chloride exit. With this logic, the medulla shouldn't be very hypertonic since you have both salts and water entering it. Why is it that as you get towards the inner medulla, the osmolarity continues to increase and increase?

 

[pfaction]

Water is reabsorbed by the vasa recta in the medulla, so the concentration increases in the medulla.

 

[fas376]

Water is reabsorbed by the vasa recta in the medulla, so the concentration increases in the medulla.

That's what I originally thought, but if you use that logic, the sodium should be reabsorbed into the vasa recta as well, right?

 

[pfaction]

Sodium would have to be actively transported, I think, which is why most of it occurs via AT in the PCT.

 

[fas376]

Sodium would have to be actively transported, I think, which is why most of it occurs via AT in the PCT.

Perfect. Didn't realize that. Thanks a lot buddy!

 

[pfaction]

If only physics, gen chem, verbal, and ochem were like this for me :|

You's welcome though.

 

[fas376]

If only physics, gen chem, verbal, and ochem were like this for me :|

You's welcome though.

Haha, I'm the opposite. Strong in physics, weak in Bio. If it's any consolation, Bio is roughly 75% of the BS, so at least that's an automatic 10+ in one section😀

Also, hate to give some bad news, but sodium DOES enter the vasa recta...

http://hrsbstaff.ednet.ns.ca/sdosman/Higher level BIO/kidenynotes11.3_files/image013.jpg

 

[MedPR]

In the descending limb of the loop of Henle, water exits. In the ascending limb, sodium and chloride exit. With this logic, the medulla shouldn't be very hypertonic since you have both salts and water entering it. Why is it that as you get towards the inner medulla, the osmolarity continues to increase and increase?

Deeper in the medulla needs to be more osmotic so that you can reabsorb water and concentrate the urine. If the concentration gradient wasn't setup this way, you would not be able to have isotonicity at the end of the descending/start of the ascending limb.

The "why" behind it is the same as the "why" behind why we walk on our legs instead of our hands. It just is.

 

[fas376]

Deeper in the medulla needs to be more osmotic so that you can reabsorb water and concentrate the urine. If the concentration gradient wasn't setup this way, you would not be able to have isotonicity at the end of the descending/start of the ascending limb.

The "why" behind it is the same as the "why" behind why we walk on our legs instead of our hands. It just is.

I guess I just assumed that the concentration outside was being caused by the ion movement. I'm probably looking too much into it. Thanks!

 

[mcloaf]

Deeper in the medulla needs to be more osmotic so that you can reabsorb water and concentrate the urine. If the concentration gradient wasn't setup this way, you would not be able to have isotonicity at the end of the descending/start of the ascending limb.

The "why" behind it is the same as the "why" behind why we walk on our legs instead of our hands. It just is.

Lol, MedPR, you're starting to sound like me. 😛