Physiology 3 - Loop of Henle

Question 1

What process occurs in the loop of henle?

Answer 1

Reabsorption not secretion

CONCENTRATION OF URINE

Question 2

What are the limits of urine concentration?

Answer 2

• During dehydration urine can be as much as 1200-1400 mOsmoles/L (plasma is 300mOsmoles/L)
• During overhydration it can go down as far as 30-50mOsmoles/L

Question 3

Whats the minimun volume of urine a day and why?

Answer 3

500ml/day Because essentially excreted products like urea, phosphate and nNa~ amount to 600mOSmoles/day which requires 500ml of water

Question 4

How do Juxtamedullary Nephron’s Loops of henle concentrate urine?

Answer 4

By acting as Counter-Current multipliers

Question 5

What happens in each limb of the loop of henle?

Answer 5

• Ascending Limb - actively transports out NaCl
• Descending Limb - loses H2O due to the osmotic pressure of the NaCl

Question 6

How concentrated is the fluid entering the loop of henle from the proximal tubule?

Answer 6

300mOsm/L aka isosmotic with plasma

Question 7

Explain how the loop of henle goes about concentrating fluid?

Answer 7

NaCl pumped out asc limb Water moves out desc limb to compensate Desc limb becomes concentrated Fluid comes round to asc limb More NaCl secretion occurs because its more concentrated. End up with hypotonic fluid (~100mosm/l) in entering the distal tubule And a hypertenoic interstitial fluid, that gets progressively more concentrated the further down the loop (1200mOsm/l) at the medullary tip.

Question 8

Whats the concentration gradient between the loop asc limb and the interstitial fluid at each vertical level?

Answer 8

The concentraion values decrease as you ascend but the gradient is always 200mOsm/l

• This is the limit of the NaCl active transporters

Question 9

How does a furosemide diuretic work?

Answer 9

They inhibit NaCl transport So the Conc gradient betweent he interstitial and tubular fluid is lost and you can no longer concentrate urine and you piss out loads of isotonic urine

Question 10

Loops of henle create the high conc interstitium and low hypotonic distal tubule fluid, what controls the final conc of the urine?

Answer 10

The hormones (mainly ADH) which control permeability of the collecting duct

• E.g. More ADH means more water resorption in the collecting duct –> Conc. urine

Question 11

Describe the structure of vasa recta around the loop of henle?

Answer 11

They follow the same hairpin loop This way they equilibriate with the interstitial conc gradient so they dont disturb the concentration process

Question 12

What is the function of the vasa recta?

Answer 12

To provide O2 to the medulla Removes fluid from the interstitium (up to 36L/day)