By: DR QAZI IMTIAZ RASOOL

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

Body as an open sytem
Body exchanges materials and energy with its surroundings

Route
Insensible lungs
Insensible skin
Sweat
Feces
Urine
Range
(l/day)
0.3-0.4
Regulatory influences
Atmospheric vapor pressure
(temperature)
0.35-0.4
0.1-2 (per hour)
10x increase in burn victims
Temperature, exercise
0.1-0.2
0.5-1.4-20
Diarrheal disease
Body fluid composition

Total Body H
2
O 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

PERCENTAGE OF H2O IN TISSUES

FLUID COMPARTMENTS
EXTRA CELLUAR INTRA CELLULAR
FLUID (cytosol)FLUID
PLASMA INTERSTITIAL TRANSCELLULAR
FLUID FLUID
1.
2.
3.
4.
5.
6.
CSF
Intra ocular
Pleural
Peritoneal
Synovial
Digestive Secretions

PERCENTAGE OF WATER IN TISSUES
Average 70 kg person total body weight
42 litres total H
2
O
28 l.
Intracellular fluid (ICF )
60%
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)
3.5
l. Plasma water
TISSUE % WATER % BODY Wt. L of H
2
O
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
Adipose Tissue 10.0 10+ 0.7
15%
5%

2
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

1.
Semipermeable membrane
2.
Movement some solute obstructed
3.
H
2
O (solvent) crosses freely
4.
End point:
1.
H
2
O moves until solute concentration on both sides of the membrane is equal
2.
OR, an opposing force prevents further movement

Solutes – dissolved particles
1.
Electrolytes – charged particles
1.
Cations – positively charged ions
2.
Na + , K + , Ca ++ , H +
Anions – negatively charged ions
Cl , HCO
3
, PO
4
3-
2.
Non-electrolytes - Uncharged
1.
Proteins, urea, glucose, O
2
, CO
2
12

APPROXIMATE IONIC COMPOSITION OF THE
BODY H2O COMPARTMENTS
Interstitial Skeletal
Plasma,
Ion mmoles/L
fluid,
mmoles/L
Cations
Na
+
K
+
Ca
2+
(ionized)
Mg
2+
(ionized)
142.0
4.3
2.5
1.1
145.1
4.4
2.4
1.1
Others
Total
4.0
154
Anions
Cl
-
HCO
3
-
HPO
4
2-
, H
2
PO
4
-
Proteins
Other
114.0
24.0
1.0
1.5
10.0
Total 154
153
117.4
27.1
1.2
0.1
6.2
153 muscle cell, mmoles/L
10.0
140.0
1.0
17
168
4.0
7.0
40.0
3.0
84.0
138

Plasma
H
2
O
Interstitial
H
2
O
Cell
H
2
O

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.

Plasma is clinically accessible
Dominated by [Na + ] and the associated anions
Under normal conditions, ECF osmolarity can be roughly estimated as:
P
OSM
= 2 [Na + ] p
270-290 mOSM

Ionic composition very different
-Total ionic concentration very similar
-Total osmotic concentrations virtually identical
1.
Semipermeable membrane.
2.
Movement some solute obstructed.
3.
H
2
O (solvent) crosses freely.
4.
End point:
H
2
O moves until solute concentration on both sides of the membrane is equal.
OR , an opposing force prevents further movement.

2
1 Excessive loss of H
2
O from
ECF
2 ECF osmotic pressure rises
3
Cells lose H
2
O to ECF by osmosis; cells shrink
(a) Mechanism of dehydration

ECF Osmolarity
?
1.
H
2
O 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.
H
2
O moves into the cells
2.
ICF Volume increases
(Cells swell)
3.
ICF Osmolarity decreases
4.
Total body osmolarity remains lower than normal

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 .

DILUTION PRINCIPLE
Principle of mass conservation
Based on using a marker whose concentration can be measured .
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

Measuring Compartment
Size
Indirect METHOD – INDICATOR (DYE) DILUTION TECHNIQUE
(Law of Mass Conservation)
Based on concentration in a well-mixed substance that distributes itself only in the compartment of interest.
Compartment
Amount of
Tracer Added
(A)
Volume (V)
Tracer Concentration (C)
Concentration = Amount Injected
Volume of Distribution
Amount of Tracer Remained in Compartment = A - E
Compartment Volume = (A – E)/C
Amount of
Tracer Lost
From
Compartment
(E)

Indicators used for measuring plasma volume, ECF volume and total body H
2
O
Compartment Criterion Indicators
1.
1.
1.
Plasma Substance should not cross capillaries
1.
2.
3.
ECF volume
Substance should cross capillaries but not cross cell membranes
Total body H
2
O
(TBW)
Substance distributes evenly in ICF &
ECF
Evans blue dye; radioiodinated fibrinogen; radioiodinated albumin
Isotonic solutions of sucrose, inulin, mannitol, NaCl
Heavy H2O, tritiated H2O, aminopyrine, antipyrine

2
1.
Deuterated H2O (D
2
O)
2.
Tritiated H2O (THO)
3.
Antipyrine

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 . Cr 51 (radioactive chromium) is incubated with red blood cells then injected
Measures total blood volume

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

1.
2.
3.
4.
Determine by subtraction:
How would you measure ICF volume?
Cannot be measured; it is calculated
(estimated)..
ICF volume = Total body H
2
O – ECF volume
5.
6.
1.
Interstitial volume
Can not be measured directly
Interstitial Fluid Volume (ISFV).
ISFV = ECFV - PV

Extracellular volume
Na 24
Cl 35
Inulin
Sucrose
Mannitol
Sulfate
I 125 iothalamate
Disperse in plasma and interstitial fluid, but not permeable to cell membrane
30-60 min for dispersion to extracellular fluid

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.

Definition: LBM is fat free mass
Total body mass = fat mass + fat free mass
Note: fat is relatively anhydrous
Note: the H
2
O content of LBM is constant
H
2
O content of LBM is constant - 70 ml /100 g tissue

:
In a healthy adult male weighing 70 kg, total body
H
2
O (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 H free
2
O is in LBM & that fat is H
2
O
3.
We know that H
2
O 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