Unit 5 Lecture 35

Question 1

Define countercurrent mechanisms

Answer 1

mechanisms that require a countercurrent flow and osmotic gradient

Question 2

Define countercurrent flow

Answer 2

Within a tubule, (ie loop of henle) there are opposing flows that counteract one another

ex: descending is permeable to water and ascending is not

Question 3

Define osmotic gradient

Answer 3

Within fluid outside of the tube, there is a different is osmotic charges between the extratubular fluid and the fluid inside the tube

Question 4

What two processes are examples of countercurrent mechanisms?

Answer 4

• countercurrent multiplication

- countercurrent exchange

Question 5

What does countercurrent multiplication deal with?

Answer 5

Nephron and ISF

Question 6

What does countercurrent exchange deal with?

Answer 6

Vasa recta and ISF

Question 7

How is an osmotic gradient built?

Answer 7

1. Permeability differences in different sections of loop an CD
2. Countercurrent flow of tube fluid through des/asc/ limbs

Question 8

What is the descending limb permeable to and why?

Answer 8

Water - higher osmolarity of fluid outside limb causes water to move out through osmosis

Question 9

What is thick ascending limb permeable to and why?

Answer 9

Solutes - symporters reabsorb Na/K/Cl

Question 10

What is the late DCT and CD permeable to?

Answer 10

water in the presence of ADH

Question 11

What direction does the descending and ascending limb carry fluid?

Answer 11

descending - Down

ascending - up

Question 12

What are the 3 major solutes involved in osmotic gradient?

Answer 12

Na/Cl/Urea

Question 13

Part 1. of countercurrent multiplication

Answer 13

Symporters in thick ascending cause a buildup of Na and Cl in renal medulla

Question 14

Part 2. of countercurrent multiplication

Answer 14

Countercurrent flow through descending and ascending limns make an osmotic gradient in renal medulla

Question 15

Part 3. of countercurrent multiplication

Answer 15

cells in CD reabsorb more water and urea

Question 16

Part 4. of countercurrent multiplication

Answer 16

Urea recycling makes buildup of urea in renal medulla

Question 17

What is urea recycling?

Answer 17

Urea leaves the CD (gets reabsorbed) due to intercalated cells and this urea concentration in the ISF causes more water to leave (be reabsorbed) in the descending limb ——> concentrated urine

Question 18

What happens during countercurrent exchange of vasa recta and ISF?

Answer 18

similar countercurrent flow and osmotic gradient

Question 19

Overall purpose of the countercurrent multiplication

Answer 19

establishes osmotic gradient through the long loop of henle

Question 20

Overall purpose of the countercurrent exchange

Answer 20

maintains the gradient by delivering nutrients to nephron cells through the vasa rects