CVPR Week 7: Concentrating and Diluting

Question 1

Objectives

Answer 1

Question 2

Does total body water fluctuate?

Answer 2

• It is maintained relatively constant by urine volume changes
• As water intake and output must be equal

Question 3

How much urine must be excreted per day

Answer 3

~600 mOsm

Question 4

Purpose of urine concentration

Answer 4

Urine is concentrated or diluted to maintain water and osmolar balance

Question 5

How much can kidneys concentrate urine?

Answer 5

can concentrate 4-fold

Question 6

How much can kidneys dilute urine?

Answer 6

kidneys can dilute urine 10-fold

Question 7

How is urine concentrated or diluted?

Answer 7

• Selectively removing solutes dilutes urine
• Selectively reabsorbing water concentrates urine

Question 8

How does water secretion or reabsorption occur?

Answer 8

Water follows Na+ reabsorption or secretion or filtration

Question 9

Does water reabsorption require energy?

Answer 9

No, it is a passive process

Question 10

How is filtrate concentrated?

Answer 10

Interstitium solute draws water out to concentrate the filtrate (DLOH, CD)

Question 11

How is interstitial solute and water reabsorption regulated?

Answer 11

by Counter-Current-Multiplier (CCM)

Question 12

CCM AKA

Answer 12

Counter current multiplier

Question 13

CCM

Answer 13

Requires different H2O permeability & solute reabsorption in the limbs of LOH

Question 14

Describe the counter-current multiplier

Answer 14

Question 15

How is the medullary concentration gradient maintained?

Answer 15

The Vasa Recta preserves the medullary concentration gradient