Loop of Henle

Question 1

What is the maximum concentration of urine that can be excreted by the kidney?

Answer 1

1200-1400mOsmoles/L

Question 2

What characteristics of the loops of Henle make them counter-current multipliers?

Answer 2

The ascending limb of the loop actively co-transports Na and Cl ions out of the tubule lumen into the interstitium. The ascending limb is impermeable to water.
The descending limb is freely permeable to water but relatively impermeable to NaCl

Question 3

Describe the mechanism of the loop of Henle counter current multiplier

Answer 3

1. The loH is filled with isosmotic fluid
2. NaCl is actively removed from the ascending limb and put into the tubule
3. Descending limb is now exposed to greater osmolairty in the interstitium so water will move out to equate this
4. The greater concentration of the descending limb means a greater concentration of the interstitium by addition from the ascending limb

Question 4

What does the counter current multiplier function of the loop of Henle achieve?

Answer 4

Concentrates fluid on descent and re-dilutes it on ascent by removing NaCl
Some of the initial filtrate is removed
Fluid which enters the distal tubule is more dilute than plasma
Creates an increasingly concentrated gradient in the interstitium
Delivers hypotonic fluid to the distal tubule

Question 5

How are the vasa recta involved in counter-current multiplication?

Answer 5

They act as counter-current exchangers. They are arranged as hairpin loops and so do not interfere with the interstitial gradient but equibrilate with it

Question 6

What are the functions of the vasa recta?

Answer 6

1. Provide oxygen for the medulla
2. Hairpin arrangement so as not to disturb gradient
3. Removes volume from the interstitium

Question 7

What two factors prevent the vasa recta from disturbing the interstitial gradient?

Answer 7

The hairpin loop arrangement

Flow rate through vasa recta is very low so there is plenty of time for equilibrium to occur