1. Body Fluids

2. Objectives By the end of the sessions the students should be able to:
Classify body fluid compartments
Recall the indicator that is used to measure the volume of a body compartment and explain the principle involved in measuring the volume.
Estimate the changes in ECF & IFC osmolarity and volumes in clinically relevant conditions.
Measure interstitial fluid volume and ICF volume

3. Total body water
Total Body Water (TBW) = 60% (50 to 70) of body weight; depends on fatty tissue.
The 70 kg 'standard male' contains 42 liters of water  % of his body weight.
Adult female contains 55% of her body weight as water due to a higher fat content.

4. Total body water (cont’d)
TBW is highest in the newborn ( %) , child (75%)
Total body water as a percentage of total body weight decreases progressively with increasing age.
By the age of 60 years, total body water (TBW) has decreased to only 45-50% of total body weight.

5. ECF & ICF
The major division is based on which side of the cell membrane the fluid lies
Intracellular Fluid (ICF: approximately 2/3 of total body water)
Extracellular Fluid (ECF: approximately 1/3 of total body water).

6. Interstitial Fluid [ISF]; Intracellular Fluid [ICF];
Plasma [about 1/4th of ECF volume]
ECF
Interstitial Fluid [ISF];
About 3/4th of ECF volume
Intracellular Fluid [ICF];
2/3 of total body water is inside cells

7. Body fluid vol in a healthy 70kg adult male
Compartment
Volume
Subdivisions
Intracellular fluid, ICF
(2/3 of TBW)
28 L -
Extracellular fluid, ECF
1/3 of TBW
14 L
10.5 L
(Interstitial fluid)
3.5 L
(Plasma)
Total body water (TBW);
60% of body weight
42 L

8. Intracellular Fluid Water forms about 75 - 80%
The major cations are K+ and Mg2+
The major anions are protein and organic phosphates such as ATP, ADP and AMP;
pH of ICF is in dependence on the metabolic processes;

9. Extracellular Fluid
Water constitutes about 93% of the plasma compartment
The major cation is Na+;
The major anions are Cl- and HCO3-;
The ions in ECF determine osmotic pressure and pH of the inner environment;
pH of ECF is 7.4

10. Trans-cellular water
is a compartment of ECW. Divided from the others by capillary endothelia and by epithelia.
Plasma
Comprises 1/4 of the ECF
It is therefore 1/12 of TBW
The major plasma proteins are albumin and globulins

11. Interstitial fluid
Comprises 3/4 of the ECF;
It is 1/4 of TBW
The composition is the same as plasma except it has little protein thus, interstitial fluid is an micro filtrate of plasma.

12. Net Osmotic Force Development
Through Semi-permeable membrane
Movement of some solute obstructed
H2O (solvent) crosses freely across membrane
End point:
Water moves until solute concentration on both sides of the membrane is equal
OR, an opposing force prevents further movement 34 34

13. Glucose Example
Gl Gl Gl Gl
Gl Gl Gl
Initial
Final
20 L
30 L
10L 36 36

14. ICF Vs ECF
The two compartments are separated by cell membrane which is freely permeable to water
In a steady state ECF and ICF osmolarity is same i.e around 300 milliosmoles.

15. ICF Vs ECF
Effective osmolarity: The difference in the concentration of impermeable particles determines the osmotic movement of water across the membrane.
NaCl represents most of the effective osmolarity of ECF
Plasma proteins which determines the effective osmolarity between interstitial and plasma fluid

16. Principles of Body Water Distribution
Body control systems regulate ingestion and excretion:
constant total body water
constant total body osmolarity
Osmolarity is identical in all body fluid compartments (steady state conditions)
Body water will redistribute itself as necessary to accomplish this 49 49

17. Shifts of water between compartments
Water shifts between ECF and ICF so that the osmolarity of the two compartments become equal
The osmolarity of ICF and ECF are assumed to be equal after a brief period of equilibration

18. It is important to understand how body osmolarity and ICV and ECV change in clinically relevant situation.
Darrow-Yannet Diagram shows the osmolarity and volume changes of body fluids.
X axis represents volume.
Y axis represents solute concentration.

19. Darrow-Yannet Diagram
Concentration of solute/ Osmolarity
ICF ECF
Volume
Volume

20. Remember: All volume disturbances originate in the ECF compartment.
When there is a net gain of fluid by the body, ECF always enlarges.
A net loss of body fluid decreases extracellular volume.

21. Remember: Changes in ICF are in response to changes in ECF.
Intracellular volume varies with the effective osmolarity of the extracellular compartment.
An increase in extracellular osmolarity decreases intracellular volume and the opposite occurs with the decrease in extracellular osmolarity.

22. How to make the graph in your head
Step 1. 
Figure out what happens to the osmolarity and volume in the ECF compartment (ECF is the smaller compartment)
Step 2.
Think how is ICF affected?

23. Problems Loss of whole blood Adult diarrhea
Infusion of excessive isotonic saline
Loop diuretics
Addison's disease
Syndrome of inappropriate ADH secretion
Insensible water loss in fever,
Diabetes insipidus,
Alcohol. 
Excessive intake of NaCl

24. Loss of whole blood & Adult Diarrhea
What will happen to volume in ECF compartment?
It will decrease.
What will happen to osmolarity in ECF compartment?
It will not change because Isotonic fluid is lost
What will happen to ICF volume and osmolarity?
No osmotic gradient, therefore, will not change
What will happen to plasma protein and haematocrit
Plasma protein concentration and Haematocrit increase because of the loss of ECF

25. Loss of whole blood & Adult Diarrhea (also called Isosmotic volume contraction)
Patient is isotonic
Osmolality
14L
Volume
28L

26. Infusion of excessive isotonic saline
What will happen to volume in ECF compartment?
It will increase.
What will happen to osmolarity in ECF compartment?
It will not change because Isotonic fluid is lost.
What will happen to ICF volume and osmolarity?
No osmotic gradient, therefore, will not change.
What will happen to plasma protein and haematocrit
Plasma protein concentration and haematocrit decrease because of addition of the fluid

27. Infusion of excessive isotonic saline (Also called Isosmotic volume expansion)
Patient is isotonic
Osmolality
Volume

28. Loop diuretics & Addison's disease
Loops make you lose sodium and water, but more of sodium than water.
Addison's disease is adrenal insufficiency.
Aldosterone makes you retain sodium so in the absence of aldosterone, you will lose sodium.

29. Loop diuretics & Addison's disease
What will happen to osmolarity in ECF compartment?
It will decrease because the kidneys lose more NaCl than water
What will happen to volume in ECF compartment?
It will decrease because water shifts into the cells and ICF osmolarity decreases until it equals ECF osmolarity
What will happen to ICF volume?
It will increase. (Decrease in osmolarity shifts the fluid into ICF)
What will happen to plasma protein and haematocrit
Protein concentration and haematocrit increases because of the decrease in ECF volume

30. Loop diuretics & Addison's disease (also called hyposmotic volume contraction)
Patient is hypotonic
Volume

31. Syndrome of inappropriate ADH secretion  (also called hyposmotic volume expansion) . Compulsive water drinker
SIADH: You are conserving too much water due to ADH.
Water drinker: You are having too much water

32. Syndrome of inappropriate ADH secretion .
What will happen to osmolarity in ECF compartment?
It will decrease because of retention of excess water
What will happen to volume in ECF compartment?
It will  increase because of water retention
What will happen to ICF volume?
It will increase. (Decrease in osmolarity shifts the fluid into ICF)
What will happen to plasma protein and haematocrit
Protein concentration decreases because of an increase in ECF volume and haematocrit is unchanged because water shifts into the red blood cells increasing their volume

33. Syndrome of inappropriate ADH secretion (SIADH)
Volume Expansion
Patient is hypotonic
Volume

34. Sweating in a HOT desert
What will happen to volume in ECF compartment? It will decrease because of the loss of sweat
What will happen to osmolarity in ECF compartment?
It will increase because sweat is hyperosmotic, relatively more water than salt is lost during sweating
What will happen to ICF volume?
It will decrease because ICF osmolarity increases until it is equal to ECF osmolarity
What will happen to plasma protein and haematocrit
protein concentration increases because of the loss if ICF volume and Haematocrit may increase but it is unchanged because water shifts from erythrocytes which decrease their volume

35. Sweating in a hot desert ( also called hyperosmotic volume contraction)
Patient is hypertonic
Volume

36. Insensible water loss in fever or Diabetes Insipidus or Alcohol
What will happen to volume in ECF compartment?
It will decrease because water is lost in all these conditions such as ADH action is lost in Diabetes insipidus, alcohol inhibits pituitary secretion of ADH, water evaporates from the warm skin surface in fever)
What will happen to osmolarity in ECF compartment?
It will increase as fluid loss is hypotonic
What will happen to ICF volume?
It will decrease because ICF osmolarity increases until it is equal to ECF osmolarity

37. Insensible water loss in fever or Diabetes Insipidus or Alcohol (Hyperosmotic volume contraction)
Patient is hypertonic
Volume

38. Excessive intake of NaCl or Infusion of sodium containing antibiotics
What will happen to osmolarity in ECF compartment?
It will increase because there has been an addition of osmoles to the ECF
What will happen to volume in ECF compartment?
Will increase because fluid moves from the ICF to ECF)
What will happen to ICF volume?
It will decrease.

39. Excessive intake of NaCl ( also called hyperosmotic volume expansion)
Patient is hypertonic
Volume

40. What will happen if a person running a marathon replaces all the volume lost in sweat by drinking water?
What will happen to total body volume?
Will remain the same because all the volume lost will be replaced by drinking water
What will happen to osmolarity in ECF compartment?
It will decrease only salt is loss as water loss has been replaced
What will happen to volume in ECF compartment?
It will decrease because water will shift from ECF to ICF
What will happen to ICF volume?
It will increase What will happen to osmolarity in ICF compartment? It will decrease

41. Person running a marathon Also called Hypoosmotic volume contraction
Patient is hypotonic
Volume

42. Measuring body fluid volumes:
Principle: Indicator-dilution principle
Method:
Administer a known amount (A) of a substance that will get distributed in a particular body fluid compartment;
Determine the final steady state concentration (C) of this indicator in blood;
Volume of distribution Vd of the indicator = Amount of indicator injected (A)
Concentration in blood after mixing (C)

43. Indicators used for measuring plasma volume, ECF volume and total body water
Compartment
Criterion
Indicators
Plasma
Substance should not cross capillaries
Evans blue dye;
radioiodinated fibrinogen;
radioiodinated albumin
ECF volume
Substance should cross capillaries but not cross cell membranes
Isotonic solutions of sucrose, inulin, mannitol, NaCl
Total body water (TBW)
Substance distributes evenly in ICF & ECF
Heavy water, tritiated water, aminopyrine, antipyrine

44. Recall How would you measure interstitial fluid (ISF) volume?
Cannot be measured; it is calculated (estimated) by
ISF volume = ECF volume – plasma volume
How would you measure ICF volume?
ICF volume = Total body water – ECF volume

45. Blood volume can be calculated (estimated) as:
Blood volume = plasma volume × (100/100-Hct)
In a healthy 70 kg adult male, plasma volume (measured using the Evans Blue dye) was found to be 3300 ml. Hematocrit was 40%. Calculate his blood volume.
5000 ml
5200 ml
5500 ml
5600 ml

46. References
BARRETT, K. E., S. M. BARMAN, et al. (2010). Ganong’s Review of Medical Physiology, The McGraw-Hill Companies, Inc.
Guyton, A. C. (2011). Textbook of Medical Physiology Elsevier Inc.
Costanzo, L. S. (2013). Body Fluids. Physiology, Elsevier.
Dunn, R. B. (2010). USMLE Step 1 Physiology Lecture Notes, Kaplan Medical.
Agro, F. E. and M. Vennari (2012). Body Fluid Management: From Physiology to Therapy, Springer.
Koeppen, B. M. and B. A. Stanton (2012). Renal Physiology, ELSEVIER MOSBY.

47. Thank you