2. OBJECTIVES
a)Discuss the distribution of total body H2O
(TWB) in the body
b) List the ionic composition of different
body compartments
c) Explain the principles of measurements
3. Body as an open sytem
Body exchanges materials and energy
with its surroundings
5. FACTORS AFFECTING
Total Body H2O
varies depending on body fat:
1. Infant: 73-80%
2. Male adult: 60%
3. Female adult: 40-50%
4. Effects of obesity
5. Old age 45%
6. Climate Level of physical activity
7. FLUID COMPARTMENTS
EXTRA CELLUAR INTRA CELLULAR
FLUID (cytosol)FLUID
PLASMA INTERSTITIAL TRANSCELLULAR
FLUID FLUID
1. CSF
2. Intra ocular
3. Pleural
4. Peritoneal
5. Synovial
6. Digestive Secretions
8. TISSUE %WATER %BODYWt. LofH2O
Skin 72 18 9.1
Muscle 76 41.7 22.1
Skeleton 22 16 2.5
Brain 74.8 2.0 1.0
Liver 68.3 2.3 1.0
Blood 83.0 8.0 4.65
Intestine 74.5 1.8 1.0
AdiposeTissue 10.0 10+ 0.7
Average 70 kg person total body weight
42 litres total H2O 60%
28 l. Intracellular fluid (ICF) 40%
14 l. Extracellular fluid (ECF) 20%
% is important in fluid therapy
divided into ¾ ISF and ¼ plasma water
10.5 l. Interstitial fluid (ISF) 15%
3.5 l. Plasma water 5%
PERCENTAGE OF WATER IN TISSUES
9. Regulation of H2O Intake
The hypothalamic thirst center is stimulated:
1. By a decline in plasma volume of 10%–15%
2. By increases in plasma osmolality of 1–2%
3. Via baroreceptor input, angiotensin II, and other
stimuli
10.
11. 1. Semipermeable membrane
2. Movement some solute obstructed
3. H2O (solvent) crosses freely
4. End point:
1. H2O moves until solute concentration on
both sides of the membrane is equal
2. OR, an opposing force prevents further
movement
15. Balance of Starling Forces acting across the capillary
membrane
1. osmotic forces
2. hydrostatic forces
Plasma vs Interstitial Space
-Balance between Hydrostatic and Colloid Osmotic
forces across the capillary membranes
Intracellular vs Extracellular
1. Osmotic effect (e.g. electrolytes)
2. ICFV is NOT altered by: iso-osmotic changes in
extracellular fluid volume.
16. Plasma is clinically accessible
Dominated by [Na+] and the associated
anions
Under normal conditions, ECF osmolarity
can be roughly estimated as:
POSM = 2 [Na+]p 270-290 mOSM
17. Net Osmotic Force Development
1. Semipermeable membrane.
2. Movement some solute obstructed.
3. H2O (solvent) crosses freely.
4. End point:
H2O moves until solute concentration on both sides of
the membrane is equal.
OR, an opposing force prevents further movement.
Ionic composition very different
-Total ionic concentration very similar
-Total osmotic concentrations virtually identical
18. Disorders of H2O Balance: Dehydration
Excessive loss of H2O from
ECF
1 2 3
ECF osmotic
pressure rises
Cells lose H2O
to ECF by
osmosis; cells
shrink
(a) Mechanism of dehydration
19. ECF Osmolarity ?
1. H2O moves out of
cells
2. ICF Volume decreases
(Cells shrink)
3. ICF Osmolarity
increases
4. Total body
osmolarity remains
higher than normal
ECF Osmolarity ?
1. H2O moves into the
cells
2. ICF Volume increases
(Cells swell)
3. ICF Osmolarity
decreases
4. Total body osmolari
remains lower than
normal
20. CRITERIA FOR A SUITABEL DYE.
BODY FLUID MARKER
1. Must mix evenly throughout the compartment
2. Non toxic, no physiological activity
3. Even mixing
4. Must have no effect of its own on the distribution of H2O
or other substances in the body
5. Either it must be unchanged during the experiment or if
it changes , the amount changed must be known.
6. The material should be relatively easy to measure.
21. DILUTION PRINCIPLE
Inject x gm of marker into compartment
measure concentration at equilibrium (y gm/L)
Since concentration = mass/ volume
Volume = mass / concentration
= x/y L
C1V1=C2V2
Principle of mass conservation
Based on using a marker whose concentration can be
measured.
22. Measuring Compartment Size
Indirect METHOD – INDICATOR (DYE) DILUTION TECHNIQU
(Law of Mass Conservation)
Concentration = Amount Injected
Volume of Distribution
Amount of Tracer Remained in Compartment = A - E
Compartment Volume = (A – E)/C
Compartment
Volume (V)
Tracer Concentration (C)
Amount of
Tracer Added
(A)
Amount of
Tracer Lost
From
Compartment
(E)
Based on concentration in a well-mixed substance that distributes
itself only in the compartment of interest.
23. Indicators used for measuring plasma volume, ECF
volume and total body H2O
Compartment Criterion Indicators
1. Plasma Substance
should not cross
capillaries
1. Evans blue dye;
2. radioiodinated fibrinogen;
3. radioiodinated albumin
1. ECF
volume
Substance
should cross
capillaries but
not cross cell
membranes
Isotonic solutions of sucrose,
inulin, mannitol, NaCl
1. Total
body H2O
(TBW)
Substance
distributes
evenly in ICF &
ECF
Heavy H2O, tritiated H2O,
aminopyrine, antipyrine
24. Total Body H2O (TBW)
1. Deuterated H2O (D2O)
2. Tritiated H2O (THO)
3. Antipyrine
25. Blood volume /Markers used
1. Obtained from plasma volume and hematocrit
2. Total blood volume = Plasma volume/1-
Hematocrit
3. Example: If the plasma volume is 4 liters and the
hematocrit is 0.45, total blood volume is ?
4. =PLASME VOL X 100
100 -HCT
1.T-1824 (Evans blue dye) attaches to plasma proteins and is removed
by the liver. Measures plasma volume
2. Radioactive labeled 125 i albumin
3. Cr51 (radioactive chromium) is incubated with red blood
cells then injected
Measures total blood volume
26. Take this problem:
100 mg of sucrose is injected into a 70 kg
man. The plasma sucrose level after
mixing is 0.01 mg/ml. If 5 mg has been
metabolized during this period, then,
what is the ECF volume?
9.5 L
14 L
17.5 L
10 L
If 1mL of solution (10mg/mL) of
dye is dispersed in chamber B
and final concentration is the
chamber is 0.01mg/mL. What is
the volume in chamber B?
1000ml or 1L
27. Compartments with
no Compartment-Specific Substance
1. Determine by subtraction:
2. How would you measure ICF volume?
3. Cannot be measured; it is calculated
(estimated)..
4. ICF volume = Total body H2O – ECF volume
5. Interstitial volume
1. Can not be measured directly
6. Interstitial Fluid Volume (ISFV).
ISFV = ECFV - PV
28. Measurement of other spaces
Extracellular volume
Na24
Cl35
Inulin
Sucrose
Mannitol
Sulfate
I125 iothalamate
Disperse in plasma and interstitial fluid, but not
permeable to cell membrane
30-60 min for dispersion to extracellular fluid
29. Determining body fat:
Technique: bioelectric impedance technique
Principle:
1. Body fluids conduct electricity well;
2. But fat is anhydrous and therefore is a poor
conductor of electricity;
3. The resistance to flow of a small current
between points on the body is proportional
to fat mass.
30. Lean body mass (LBM)
Definition: LBM is fat free mass
Total body mass = fat mass + fat free mass
Note: fat is relatively anhydrous
Note: the H2O content of LBM is constant
H2O content of LBM is constant - 70 ml /100 g
tissue
31. Take this problem:
In a healthy adult male weighing 70 kg, total body
H2O (TBW) was measured to be 42 L. What is his
lean body mass (LBM)? What is his fat mass?
1. Given TBW = 42 L
2. Assume all this H2O is in LBM & that fat is H2O
free
3. We know that H2O content of LBM is 70 ml/100 g
4. Thus, if TBW is 42 L, LBM = 60 kg
5. Since he weights 70 kg, his fat mass is 70-60 =
10 kg
