a physiological approach

1. URINE
CONCENTRATION AND DILUTION
PBL 6
2017 Oct 9

2. OBJECTIVE
Urine
• Concentration
• Dilution

3. • Kidney can excrete urine
As low as 50 mOsm/L (1/6th of plasma)
WITHOUT MAJOR CHANGES IN SOLUTE EXCRETION
As high as 1400 mOsm/L (> 4 times of Plasma)

4. •Excretion of concentrated urine

5. Requirements for concentrated urine excretion
A. Hyperosmotic renal medulla
provide high osmotic gradient for water reabsorption
B. High ADH (vasopressin)
increase water permeability to late DCT and CD

6. Hyperosmotic renal medullary interstitium
(The countercurrent multiplier system)

7. COUNTERCURRENT MULTIPLIER SYSTEM
Depends on the special anatomical arrangement of loops of Henle and vasa
recta
Thick ascending loop of Henle can reach upto 200 mOsm/L of tubule-
interstitial gradient

8. osmosis

9. COUNTERCURRENT MULTIPLIER SYSTEM

10. UREA RECIRCULATION
Recirculation :
from collecting duct to loop of
Henle (corticopapillary osmotic
gradient)
ADH causes hyperosmotic urine
in medullary collecting duct (inc.
urea conc. so inc. urea diffusion.)

11. Anti-Diuretic Hormone (ADH)

12. Fig. Very low ADH levelFig. High ADH level
Anti-Diuretic Hormone (ADH)

13. • Countercurrent exchanger in vasa recta

14. • Vasa recta – do not create the medullary hyper-osmolarity, but
they do prevent it from being dissipated
• U shape vessel minimize loss of solute from interstitium
• Increased medullary blood flow reduces urine concentrating
ability (vasodilators)
• Urine concentration depends on rate of fluid flow in Loop of
Henle

15. COUNTERCURRENT EXCHANGER IN VASA RECTA
- Low medullary blood flow
(minimize solute loss from
medullary interstitium)
and
-Countercurrent exchanger
(minimize solute washout from
medullary interstitum)

16. Combining Together

18. Dilute Urine

19. ADH level control the urine
concentration
Tubular fluid remains isosmotic in
proximal tubule
Tubular fluid diluted in ascending
loop of henle
Tubular fluid diluted in distal and
collecting tubules in low/absence
of ADH
Fig. Very low ADH level

20. REFERENCES
• Guyton and Hall, a textbook of medical
physiology,13e
• Lippincott illustrated reviews flash cards physiology
• Ganong’s review of medical physiology,25e

21. Thank you