Lecture 35 Unit 5

Question 1

what do countercurrent mechanisms require

Answer 1

• a countercurrent flow of fluid through a tubule

- as somatic gradient in fluid surrounding tubule

Question 2

what are the two countercurrent mechanisms

Answer 2

• countercurrent multiplication

- countercurrent exchange

Question 3

what happens in countercurrent multiplication

Answer 3

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

Question 4

what happens in countercurrent exchange

Answer 4

process which enables oxygen to cells of renal medulla without loss of the osmotic gradient in ISF of renal medulla

Question 5

what are the two main factors that contribute to building the osmotic gradient

Answer 5

• permeability differences

- countercurrent flow

Question 6

what are the permeability differences

Answer 6

• descending limb of loop of henle is very permeable to water
• thick ascending limb in loop of henle is impermeable to water
• late DCT and CD only permeable to water in presence of ADH

Question 7

what happens in countercurrent flow

Answer 7

-descending and ascending loop of heel carry tubular fluid in opposite directions

Question 8

what are the ADH effects on the osmotic gradient

Answer 8

• ADH stimulates Na+/K+/Cl- symporter activity in thick ascending loop of henle
• ADH stimulates facultative reabsorption of water n upper CD
• ADH stimulates water reabsorption and urea recycling in lower CD

Question 9

what does the ability of ADH to cause excretion of concentrated urine require?

Answer 9

an osmotic gradient of solutes in the ISF of the renal medulla

Question 10

what are the 3 major solutes involved in the osmotic gradient

Answer 10

Na+, Cl-, urea

Question 11

what happens in countercurrent multiplication

Answer 11

1. symporters in thick ascending limb cells of the loop of henle cause a buildup of Na+ and Cl- in renal medulla
2. countercurrent flow through the descending and ascending limbs of the loop of henle establishes an osmotic gradient in the renal medulla
3. cells in the CD reabsorb more water and urea
4. urea recycling causes a buildup of urea in the renal medulla

Question 12

where is urea impermeable

Answer 12

thick ascending limb, DCT, and CD

Question 13

what is countercurrent exchange

Answer 13

process by which solutes and water are exchanged between blood of vasa recta and ISF of renal medulla

Question 14

what does the vasa recta act as

Answer 14

a countercurrent exchanger

Question 15

what does the vasa recta do

Answer 15

provides oxygen and nutrients to renal medulla without washing out the osmotic gradient

Question 16

how does loop of henle establish osmotic gradient

Answer 16

countercurrent multiplication

Question 17

how does vasa recta maintain gradient

Answer 17

countercurrent exchange