US Practical 1 - Cortico Medullary Osmotic Gradient

Question 1

What does the ability to produce hypertonic urine depend on?

Answer 1

High OSMOLARITY of the interstitial fluid in renal medulla

Question 2

What 3 properties of the LOH does the high osmolarity of interstitial fluid in the renal medulla depend on?

Answer 2

Countercurrent flow (down descending and up ascending limbs)
Descending limb is permeable to water but impermeable to solutes
Ascending limb is water impermeable but NaCl is actively transported out of tubular fluid into interstitium

Question 3

What happens in the first in the LoH?

Answer 3

Active transport of NaCl out of the ascending limb raises interstitial osmolarity, water moves out of descending limb down osmotic gradient, raising osmolarity of tubular fluid in descending limb and lowering thr interstitium
Fluid flows down descending limb and up ascending limb, new isotonic fluid enters the loop

Question 4

What are the final values when they LoH cycle occurs 4 times?

Answer 4

Interstitial osmolarity near bend of loop is hypertonic

Osmolarity in fluid emerging from loop is hypotonic

Question 5

What does active transport do at the ascending limb?

Answer 5

Creates relatively small gradient at any level of the loop BUT countercurrent flow causes the difference to get multiplied so there is a larger gradient between cortex and inner medulla

Question 6

What are some complications that occur in LoH?

Answer 6

Both solutes and water (dependent on VP) are reabsorbed from collecting ducts, but they can’t just accumulate forever in the interstitium

Question 7

How are the complications of the LoH dealt with?

Answer 7

As blood flows out of cortex down descending vasa recta through the increasingly hypertonic medulla, solute diffuses in
In the ascending vasa recta the surrounding interstitium become less and less hypertonic, so the NaCl will diffuse back out, so medulla can be supplied with O2 and nutrients and yet high osmolarity of the medulla can be maintained