This document discusses renal physiology and osmoregulation through urine dilution and concentration. It covers plasma osmolality, how the body regulates changes in osmolality through thirst, antidiuretic hormone (ADH) secretion, and the countercurrent multiplier and exchanger mechanisms in the loop of Henle and vasa recta. These systems allow precise control of plasma osmolality and the production of dilute or concentrated urine depending on the body's needs.

1. 1
RENAL PHYSIOLOGY
(IV)
m
OSMOREGULATION
(URINE DILUTION
& CONCETRATION)
Mohammed Abdel Gawad

2. OBJECTIVES
2
 Use of Units in Physiology
 Plasma Osmolality Changes
 Plasma Osmolality Correction
 Counter-Current Multiplier & Exchange
Mechanism

3. OBJECTIVES
3
 Use of Units in Physiology
 Plasma Osmolality Changes
 Plasma Osmolality Correction
 Counter-Current Multiplier & Exchange
Mechanism

4. Mole & Millimole
4

5. 5
So Mole (& millimole) is
a number

6. Molecular weight
6
 MW of molecule
=
weigh (grams) of 1 mole of the molecule
For example,

MW of Mg is 24
Therefore,
1 mole of Mg atoms weighs 24 grams.

7. Use of units: Mole & Molecular weight
7

8. Plasma Solute Concentration (mmol/L & mg/dl)
8
Number Weight

9. 9

10. Osmolality
10
 is the number of particles (mmol) contained in
one liter of water, so measured in mmol/L.
 i.e. it is the concentration by number

11. Osmolality vs Osmolarity
11
Osmola Lity
- It is the number of osmoles or moles per kg of solvent
Osmola Rity
-It is the number of osmoles per liter of solution
- Osmole = the amount of a substance that dissociates in solution
to form one mole of osmotically active particles.
- For example, a solution of 1 mol/L NaCl corresponds to an
osmolarity of 2 osmol/L

12. Osmolality vs Specific Gravity
12
 Specific gravity is the mass of one milliliter of solution in grams. This gives
an indication of both the number and weight of the particles in the urine.
 Most of the time, this provides an accurate estimate of urine concentration;
however, if the urine contains particularly heavy particles such as glucose
or x-ray dye, the specific gravity will overestimate urine concentration

13. Osmolality, Calculation
13
 normally ranges between 285 and 295 mmol/L

14. Osmolality, Osmolar Gap
14

15. Equivalents
15
 How to express non electrolytes in equivalent

16. Equivalents: Electroneutral Body Fluids
16

17. OBJECTIVES
17
 Use of Units in Physiology
 Plasma Osmolality Changes
 Plasma Osmolality Correction
 Counter-Current Multiplier & Exchange
Mechanism

18. Normal Plasma Osmolality
18

19. Effect of plasma osmolality on cell size
19

20. OBJECTIVES
20
 Use of Units in Physiology
 Plasma Osmolality Changes
 Plasma Osmolality Correction
 Counter-Current Multiplier & Exchange
Mechanism

21. Osmolality Monitoring - General Concept
21
 A change in plasma osmolality of only 1% is detectable
by the hypothalamus.

22. How plasma osmolality changes?
General Concept
22

23. How body adjust plasma osmolality
changes? - General Concept
23

24. How body adjust plasma osmolality
changes? - General Concept
24

25. How body adjust plasma
hyposmolality (1)? – Suppress Thirst
25

26. How body adjust plasma
hyposmolality (2)? – Suppress of ADH
26

27. How body adjust plasma
hyperosmolality (1)? – Stimulate Thirst
27
 Usually the plasma osmolality must increase 5% to stimulate
thirst.
 Thirst (causing the ingestion of water) is the most effective
defense against increases in osmolality.
 This defense is so effective that, with ready access to water,
alert people cannot develop significant increases in
osmolality

28. How body adjust plasma
hyperosmolality (2)? – Release of ADH
28

29. How body adjust plasma
hyperosmolality (2)? – Release of ADH
29
3 Steps

30. Step 1: ADH – Stimuli
30
 The release of ADH in the setting of volume depletion and the inappropriate
release of ADH are two important factors which can initiate the
development of hyponatremia.

31. Step 2: ADH – Formation,
Storage & Release
31

32. Step 3: ADH – Action
Distal Tubules
32

33. Mechanism of action of ADH
(Facultative water reabsorption)
(Formation of Water Pores)
33

34. Step 3: ADH – Action
Concentrated Medullary Interstitium
34

35. TO MEMORISE
35
ADH
ADds Hydration to the body by causing the
formation of a concentrated urine.

36. OBJECTIVES
36
 Use of Units in Physiology
 Plasma Osmolality Changes
 Plasma Osmolality Correction
 Counter-Current Multiplier & Exchange
Mechanism

37. Loop of Henle (Countercurrent Multiplier)
&
Vasa Recta (Countercurrent Exchange Mechanism)
37
 Interaction between the flow of filtrate through the loop of
Henle (countercurrent multiplier) and the flow of blood
through the vasa recta blood vessels (countercurrent
exchanger)

38. RENAL CIRCULATION
38

39. Sodium Tubular Handling
39
65%
8-10%
25%

40. Water Tubular Handling
40
65% by osmosis
15%
(obligatory
Under effect of
reabsorption)
ADH
(Facultative
reabsorption)
15-20%
by osmosis
(obligatory
reabsorption)

41. Loop of Henle: Countercurrent Multiplication
41

42. Loop of Henle: Countercurrent Multiplication
42
 See the video
on our facebook group
NephroTube

43. Vasa Recta: Countercurrent Exchange
43

44. Vasa Recta: Countercurrent Exchange
44
 See the video
on our facebook group
NephroTube

45. Effect of ADH (formation of diluted
& concentrated urine)
45

46. Tonicity
46
Isotonic Solution
Cells normal shape, no loss or
gain of water.
Hypertonic
Solution
Cells lose water and shrink.
Hypotonic
Solution
Cells swell rapidly as
water rushes into them.

47. Effect of ADH (formation of diluted
& concentrated urine)
47
 See the video
on our facebook group
NephroTube

48. 48
Follow On
www.nephrotube.blogspot.com
&
Facebook Group
NephroTube

49. 49
Gawad