Countercurrent and concurrent exchanger?

[sameeralord]

Hello everyone,

I searched the net but I don't understand the difference.

BLO0D FLOW ---------------------------------->
0% .......… saturation
0% .......… saturation
WATER FLOW <-------------------------------

Countercurrent

BLO0D FLOW ---------------------------------->
0% .......… saturation
100%........… saturation
WATER FLOW --------------------------------->

Concurrent

I understand how equilibrium would be reached in concurrent but I don't understand how counter current maintains a concentration gradient. Please explain in simple language. Also if you can explain the above diagrams, I got it from net I don't understand them much. Thanks

 

[Andy Resnick]

Those diagrams don't make too much sense...maybe the concurrent (simple exchange), but the countercurrent should look like:

BLOOD ----------------->
0%---------------> 90%
10%-------------> 100%
WATER <-----------------

It's clear from the above that along the length of the tubes, there is flow from the higher to the lower.

Now, in the kidney, the tubes form a loop, with high osmolarity in the medulla:

->600 mOsm-------->1200 mOsm----------->600 mOsm--->

And this allows for the supply of blood to the medulla without altering the high osmolarity of the medulla (which would abolish the urine concentrating mechanism).

The mechanism of the countercurrent multiplier refers to the active transport of salt out of the loop of Henle into the vasa recta. This amplifies the small gradient between the limbs to create a large gradient along the length of the limb of the loop.

 

[sameeralord]

Those diagrams don't make too much sense...maybe the concurrent (simple exchange), but the countercurrent should look like:

BLOOD ----------------->
0%---------------> 90%
10%-------------> 100%
WATER <-----------------

It's clear from the above that along the length of the tubes, there is flow from the higher to the lower.

Now, in the kidney, the tubes form a loop, with high osmolarity in the medulla:

->600 mOsm-------->1200 mOsm----------->600 mOsm--->

And this allows for the supply of blood to the medulla without altering the high osmolarity of the medulla (which would abolish the urine concentrating mechanism).

The mechanism of the countercurrent multiplier refers to the active transport of salt out of the loop of Henle into the vasa recta. This amplifies the small gradient between the limbs to create a large gradient along the length of the limb of the loop.

Thanks a lot for the response Andy Your answer is just what I need but I'm finding it difficult to understand.

0%---------------> 90%
10%-------------> 100%

Could you please tell me how to get those values and what is this the percentage of? Please excuse my poor understanding in this area.

 

[Andy Resnick]

The numbers are placeholders; the material I referred to draws an analogy with thermal transport. Silbernagl and Despopoulos "Color Atlas of Physiology" (Thieme) is as close to an ideal reference as I have seen.