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1. 1
RENAL PHYSIOLOGY
(VII)
m
VOLUME REGULATION
Mohammed Abdel Gawad

2. OBJECTIVES
2
 Body water compartments
 Electrolytes & Non-Electrolytes distribution
 Starling’s forces & Membrane permeability
 Effective circulatory volume
 Volume regulation (General Concept)
 Volume regulation (Clinical Correlation)

3. OBJECTIVES
3
 Body water compartments
 Electrolytes & Non-Electrolytes distribution
 Starling’s forces & Membrane permeability
 Effective circulatory volume
 Volume regulation (General Concept)
 Volume regulation (Clinical Correlation)

4. TBW is affected by: Gender and Age
4

5. Total body water Compartments
5

6. Intravascular Compartment
6

7. Intravascular Compartment
7

8. Electrolytes and Non-Electrolytes
dissolved in the TBW
8

9. Total body water Compartments

10. Osmolality
 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. Water, Electrolytes & Non-Electrolytes
Distribution (1)
11

12. Water, Electrolytes & Non-Electrolytes
Distribution (2)
12

13. Osmolality of all three compartments
13
 Osmolality of all three compartments is the
same, because water is able to move freely
among all three compartments

14. OBJECTIVES
14
 Body water compartments
 Electrolytes & Non-Electrolytes distribution
 Starling’s forces & Membrane permeability
 Effective circulatory volume
 Volume regulation (General Concept)
 Volume regulation (Clinical Correlation)

15. Movement of water – Starling’s Forces
15
 The amount of water in each body compartment is
dependent on:
 1- osmotic pressure
 2- hydrostatic pressure (filtration)
 + 3- Membrane characteristics

16. Osmolality
 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

17. Starling’s Forces – Osmotic pressure
17

18. Starling’s Forces – Osmotic pressure
18

19. Starling’s Forces – Hydrostatic pressure
19

20. Membrane Factors
20
 Membrane permeability (s) is clinically relevant in disorders which
disrupt membrane integrity (e.g., sepsis).

21. Body Fluid Exchange
21
 1- Osmosis
 2- Filtration
 3- Diffusion (the most
important)

22. OBJECTIVES
22
 Body water compartments
 Electrolytes & Non-Electrolytes distribution
 Starling’s forces & Membrane permeability
 Effective circulatory volume
 Volume regulation (General Concept)
 Volume regulation (Clinical Correlation)

23. Effective Circulating Volume
23

24. Effective Circulating Volume:
Plasma Volume
24

25. Effective Circulating Volume:
Plasma Volume
25

26. Effective Circulating Volume:
Blood Pressure
26

27. OBJECTIVES
27
 Body water compartments
 Electrolytes & Non-Electrolytes distribution
 Starling’s forces & Membrane permeability
 Effective circulatory volume
 Volume regulation (General Concept)
 Volume regulation (Clinical Correlation)

28. Volume Regulation
General Concept
28
1 → 2 → 3

29. Volume Regulation
General Concept
29
1 → 2 → 3

30. Volume Regulation
General Concept: 1- Monitoring
30

31. Volume Regulation
General Concept
31
1 → 2 → 3

32. Volume Regulation
General Concept: 2- Signaling
32
• Renin-angiotensin II-aldosterone and sympathetic activity are the primary
signals of volume regulation; these signals are activated together.
• ADH is only employed when volume is extremely low i.e. secondary line.
• If ADH is active, then renin-angiotensin II-aldosterone and sympathetic
activation are already engaged.

33. Volume Regulation
General Concept: 2- Signaling - RAAS
33

34. Volume Regulation
General Concept
34
1 → 2 → 3

35. Volume Regulation
General Concept: 3- Action at Targets
35

36. Volume Regulation
General Concept: 3- Action at Targets – Angiotensin II
36
Angiotensin II is the most potent vasoconstrictor in the body

37. Volume Regulation
General Concept: 3- Action at Targets – Aldosterone
37
The effect of aldosterone on sodium reabsorption is so powerful that it
can reduce the urine sodium concentration to as low as 1 mEq/L

38. Volume Regulation
General Concept: 3- Action at Targets – Aldosterone
38

39. Volume Regulation
General Concept: 3- Action at Targets – Aldosterone
39
Aldosterone Overview
•An increase in the plasma potassium concentration of 0.1 mEq/L is enough to stimulate
the release of aldosterone.
• Although aldosterone release is not affected by acid-base disorders, aldosterone plays
an important role in the generation and maintenance of many acid-base disorders.
•Increased aldosterone activity results in metabolic alkalosis and decreased activity
results in metabolic acidosis (type 4 RTA).

40. Volume Regulation
General Concept: 3- Action at Targets – Sympathetic Activity
40

41. Volume Regulation
General Concept: 3- Action at Targets – ADH
41
•ADH is only released when a substantial (10-15 mmHg) fall in blood pressure occurs.
•Although it is an emergency defense, ADH is not a very effective defense against
hypovolemia. Because water distributes among all three body water compartments,
water resorption at the collecting tubules causes only a minimal rise in plasma volume.
•The primary function of ADH is the regulation of plasma osmolality.

42. Volume Regulation
General Concept: Atrial natriuretic peptide
42
Atrial natriuretic peptide is the only volume regulatory hormone that decreases
effective volume
•The physiologic significance of ANP is uncertain.
•Although congestive heart failure is associated with volume overload and elevated
levels of ANP, the kidney still excretes minimal amounts of sodium. This contradiction is
explained by the theory that ANP activity requires a normal blood pressure.
•Since CHF is typically associated with a lower than normal blood pressure, the effect
of ANP is blocked.

43. OBJECTIVES
43
 Body water compartments
 Electrolytes & Non-Electrolytes distribution
 Starling’s forces & Membrane permeability
 Effective circulatory volume
 Volume regulation (General Concept)
 Volume regulation (Clinical Correlation)

44. Volume Regulation
Clinical Correlation
44

45. Volume Regulation
Clinical Correlation
45
+ lymphatic
obstruction

46. Volume Regulation
Clinical Correlation
46

47. 47
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48. 48
Gawad