Renal IV: Concentrating Mechanisms

Question 1

What two things do countercurrent mechanisms involve?

Answer 1

countercurrent flow and an osmotic gradient

Question 2

What are the two ways countercurrent mechanisms exists in the kidney?

Answer 2

Countercurrent multiplication and countercurrent exchange

Question 3

What is countercurrent multiplication?

Answer 3

process which produces a progressively increasing osmotic gradient in interstitial fluid of the renal medulla

Question 4

What is countercurrent exchange?

Answer 4

process which enables oxygen delivery to cells of renal medulla without loss of the osmotic gradient in interstitial fluid of renal medulla

Question 5

What two main factors contribute to making the osmotic gradient?

Answer 5

permeability differences and countercurrent flow

Question 6

What is the descending limb of the loop of henle permeable to?

Answer 6

water
the higher osmolarity of interstitual fluid outside the loop causes water to leave by osmosis

Question 7

What is the ascending limb of the loop on henle permeable to?

Answer 7

permeable to solutes, impermeable to water
symporters reabsorb the solutes

Question 8

What is the late DCT and CD permeable to?

Answer 8

permeable to water only in the presence of ADH

Question 9

Where is countercurrent flow seen?

Answer 9

in the descending and ascending limbs of the loop of henle carrying filtrate in different directions

Question 10

What major solutes are involved in the osmotic gradient?

Answer 10

Na+ Cl- Urea

Question 11

ADH causing excretion of concentrated urine requires what in the interstitial fluid of the renal medulla?

Answer 11

osmotic gradient

Question 12

What 3 ways does ADH effect osmotic gradient?

Answer 12

1. stimulates Na+/K+/2Cl- symporter activity in thick ascending limb
2. Stimulates facultative reabsorption of water in upper CD
3. stimulates water reabsorption and urea recycling in lower CD

Question 13

What are the 4 aspects of countercurrent multiplication?

Answer 13

1. Symporters in thick ascending limb cause buildup of Na+ and Cl- in renal medulla
2. Countercurrent flow through ascending and descending limbs establishes osmotic gradient
3. Cells in CD reabsorb more water and urea
4. urea recycling causes a buildup of urea in renal medulla

Question 14

Countercurrent exchange occurs between what 2 fluids?

Answer 14

blood of vasa recta and interstitial fluid of renal medulla