RP6: Urine Concentration and Dilution

Question 1

Normal function requires ECF Osmolarity of _____ mOsm

Answer 1

300 mOsm

Question 2

Maximal urine concentration _____ mOsm

Answer 2

1200 mOsm

Question 3

Minimal urine concentration ___ mOsm

Answer 3

50 mOsm

Question 4

Urine Formed Without ADH is…

Answer 4

Dilute

Question 5

Filtrate is ________ in proximal tubule

Answer 5

isosmotic

Question 6

Filtrate becomes ________ as passes
through thin descending loup

Answer 6

hyperosmotic

Question 7

What happens in the thin descending loup?

Answer 7

– Water reabsorption
– No solute reabsorption

Question 8

Becomes _______ as it passes through thick ascending and early distal tubule

Answer 8

hyposmotic

Question 9

What happens in the thick ascending and early distal tubule?

Answer 9

– Solute reabsorption
– No water reabsorption

Question 10

What hormone increases H2O permeability of distal tubule and collecting duct?

Answer 10

ADH

Question 11

What is obligatory urine volume (OUV)?

Answer 11

The maximal concentrating ability of the kidney dictates how much urine volume must be excreted each day to rid the body of metabolic waste products and ions that are ingested.

Question 12

Adults must excrete ____ mosmol daily of urine

Answer 12

600 mosmol

Question 13

What is the equation for obligatory urine volume (OUV)?

Answer 13

OUV (vol/day) = Osmotic Load (mOsmol/day)/Max. [Urine] (mOsm)

Question 14

What is the obligatory urine volume when maximum urine
concentration = 300 mOsm?

Answer 14

600 mosmol/day / 300 mOsm

= 2 L/day

Question 15

What are the requirements for excreting a concentrated urine?

Answer 15

1. high levels of ADH
2. hyperosmotic medullary interstitial fluid
3. counter courrent multiplier mechanism

Question 16

Continuous delivery of ______ from proximal convoluted tubule into loop of Henle

Answer 16

NaCl

Question 17

Concentration of filtrate by H2O ________ by Descending Limb of Henle

Answer 17

reabsorption

Question 18

In the absence of ADH the distal tubule and collecting duct do what?

Answer 18

• reabsorb solute
• little to no water reabsorption

Question 19

In the presence of ADH the distal tubule and collecting duct do what?

Answer 19

• become highly permeable to water and reabsorb much water into the cortical interstitium

Question 20

What sections of the nephron are permeable to urea?

Answer 20

• proximal tubule
• thin ascending and descending limbs of the loop of henle
• medullary collecting duct

Question 21

What sections are impermeable to urea?

Answer 21

thick ascending limb of loop of henle
early and late distal tubule
cortial collecting duct

Question 22

What is the countercurrent multiplier mechanism?

Answer 22

➢ Filtrate in descending & ascending
limbs of loop of Henle flows in
opposite directions of blood flow
in Vasa Recta
➢ Clears Reabsorbed water so does
not dilute medullary interstitial
fluid
➢prevents osmolarity changes in the vase recta (blood)

Question 23

What is the filtrate osmolarity in the proximal tubule?

Answer 23

isomotic

Question 24

What is the filtrate osmolarity in the descending loop of henle?

Answer 24

hyperosmotic

Question 25

What is the filtrate osmolarity in the ascending limb of the loop of henle?

Answer 25

hyposmotic

Question 26

What is the filtrate osmolarity in the distal tubule and collecting ducts?

Answer 26

variable (depends on ADH)

Question 27

What percent of water is reabsorbed in the proximal tubule?

Answer 27

70%

Question 28

What percent of the water is reabsorbed in the descending loop of henle?

Answer 28

20%

Question 29

What percent of the water is reabsorbed in the ascending loop of henle?

Answer 29

0%