23. Concentrating the Urine

higher concentration in water relative to blood

countercurrent multiplier- loop of henle

1. isotonic medullary interstitium, if nothign happens we have equillibrium as everuthing is isotonic to loop of henle

2. active transport of ions (NaCl) pumped out of ascending limb, water does not follow only NaCl is coming across

3. passive diffusion of water out o❤‍🩹f the descending limb, water wants to come out bc of 300 vs 400 (osmotic pull)

4. watch increasing concentration of tubule fluid as it moves down on the left and uo to the right, more 300 is coming in 400 is moving up, move dhigher concentration liquid into ascending limb

5. actively transporting, medullary interstitium is at 5 bc we have maintained that, more concentrated on left so more NaCl moving out

6. repeating 3, more passive movement of water into medullary intersttitium to increase conc of liquid in tubule part

bc of tube going back and forth, we are able to regulate the medullary interstitium

This creates a hyperosmotic medullary interstitium!

vasa recta= blood flow that overlies loop of henle (countercurrent exchanger)

1. vasa recta capillaries lose water as they descend into the medulla

2. lose ions as they ascend into the cortex (concentration gradient favors net movement out)

3. thus, due to countercurrent positioning of the capilaries, the solute moving out the ascending limb can be picked up by descending limb

4. this preserves the hyperosomotic medullary interstitium

the ability of mammalian kidney to concentrate urine depends on length of loops of Henle

Kidney of a desert gerbil has loops of Henle so long they extend down into the ureter which is cut off in this figure!!!! way farther than lab rat