Body fluid compartments

1. The Body fluid compartments
Dr. Sai Sailesh Kumar G

2. Learning objectives
List the body fluid compartments and their relative contribution to the
total body water
Describe how the volumes of these compartments can be estimated
List the features of an ideal indicator to measure the body fluid
compartments

3. Introduction
The maintenance of a relatively constant volume and a stable
composition of the body fluids is essential for homeostasis.

4. Fluid Balance
Fluid intake = Fluid output

5. Daily intake of water
Water is added to the body by two major sources
Ingested in the form of liquids or water in the food (about 2100 ml/
day)
It is synthesized in the body by oxidation of carbohydrates (200
ml/day)
Total water intake is about 2300 ml/day

6. Daily intake of water
However, intake of water is highly variable among different
people and even within the same person on different days,
depending on climate, habits and level of physical activity.

7. Daily loss of water
Insensible water loss
Continuous loss of water by evaporation from respiratory tract
and diffusion through skin (700 ml/ day) under normal conditions
We are not consciously aware of it
But it occurs continuously in all humans

8. Daily loss of water
Insensible water loss through skin occurs independently of sweating
Occurs even in people who born without sweat glands
The average water loss 300-400 ml/day
This loss is minimized by cholesterol-filled cornified layer of the skin
Damage to this layer in condition like burns can increase loss of fluid
to 3-5 lit/ day

9. Daily loss of water
Insensible water loss through respiratory tract about 300-400 ml/day
As air enters the respiratory tract, it becomes saturated with moisture
to a vapour pressure of about 47 mmHg before it is expelled
In cold weather, the atmospheric vapour pressure decrease to nearly
0
Great loss of water from lungs

10. Daily loss of water
Fluid loss in sweat
Highly variable depending on physical activity and environmental
temperature
Normal is 100 ml/day
In hot weather or during heavy exercise fluid loss increases to 1-2 l/hr

11. Daily loss of water
Water loss in feces
Only small amount is lost
100 ml/ day
In severe diarrhea the loss can increase to several liters a day

12. Daily loss of water
Water loss by kidneys
Multiple mechanisms control the rate of urine excretion
Urine volume can be as low as 0.5 lit / day in dehydrated person
As high as 20 l/day in a person drinking tremendous amounts of
water

13. Body fluid compartments
Total body fluid is distributed mainly between two compartments
Extra cellular fluid (ECF)
Intra cellular fluid (ICF)
ECF divided into interstitial fluid and plasma

14. Body fluid compartments
There is another small compartment
Transcellular fluid
Fluid in synovial, peritoneal, pericardial, intra ocular spaces and
CSF
All trans cellular fluids together constitutes about 12 lit

15. Body fluid compartments
In a 70 kg adult man, the total body water is about 60 % of body
weight
About 42 lit
This percentage depends on age, gender, and degree of obesity

16. Body fluid compartments
Intracellular fluid compartment
About 28 lit of the 42 lit of fluid is inside the 100 trillion cells
Intracellular fluid
Thus, the intracellular fluid constitutes about 40% of the total
body weight

17. Body fluid compartments
Extracellular fluid
All the fluids outside the cells are called ECF
20 % of body weight (14L) in 70 kg man
Interstitial fluid 11 L
Plasma 3 L

18. Body fluid compartments
Plasma is the non-cellular part of the blood
There will be exchange of the substances between the plasma
and interstitial fluid through capillary pores
The composition of plasma and interstitial fluid is almost same
except for proteins

19. Blood volume
 the average blood volume in adults is about 7% of body weight
About 5 lit
60% of blood is plasma
40% is RBC

20. Extracellular fluid
 Sodium, Chloride

21. Intracellular fluid compartment
 ICF is separated from ECF by cell membrane
Membrane is permeable to water but not for electrolytes
ICF contains only small quantities of sodium and chloride ions
Almost no calcium
Large amounts of potassium and phosphate ions

22. Indicator-dilution principle
 Place an indicator substance in the compartment
Allow it to disperse evenly through out the compartment’s fluid
Analyze the extent to which the substance gets diluted
Indicator-dilution method

23. Indicator-dilution principle
 Small amount of dye or other substance contained in syringe is
injected into a chamber
The substance is allowed to disperse throughout the chamber
Until it becomes mixed in equal concentrations in all the areas of
chamber

24. Indicator-dilution principle
 A sample of fluid containing the dispersed substance is removed
Concentration is analyzed chemically, photoelectrically or both means
If none of the substance leaked out of the compartment, the total
mass of the substance in the compartment will be equal to the total
mass of the substance injected

25. Indicator-dilution principle
 Volume B = Volume A x Concentration A / Concentration B

26. Indicator-dilution principle
 if 1 ml of the solution containing 10 mg/ml of dye is dispersed
into chamber B and the final concentration in the chamber is 0.01
mg for each ml of fluid
What is the volume of the chamber

27. Indicator-dilution principle
 Volume B = 1ml x 10 mg/ml/ 0.01 mg/ml
1000 ml

28. Features of ideal indicator
 The indicator should disperse evenly through out the compartment
The indicator disperses only in the compartment that is being measured
The indicator should not metabolized or excreted for a sufficient duration
Indicator can be easily and accurately measured
Indicator is nontoxic

29. Measurement of total body water
 Radioactive water or heavy water can be used to measure total
body water
Another substance that can be used is Antipyrine

30. Measurement of Extracellular fluid volume
 Radioactive sodium, radioactive chloride, radioactive
iothalamate, thiosulfate and insulin.

31. Calculation of intracellular volume
 can not be measured directly
Can be calculated
Intracellular volume = Total body water – extracellular volume

32. Measurement of plasma volume
 Evans blue dye (also called T-1824)

33. Measurement of interstitial fluid volume
 ECF volume – plasma volume

34. Measurement of Blood volume
 Total blood volume = Plasma volume/ 1-hematocrit