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8/7/2019 4. Body Fluids Medical 1011
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BODY FLUIDS(for MBBS Phase I)
Rosnah Ismail
Physiology Department, Faculty of Medicine
Universiti Malaya
January 2011
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Internal environment ofbody (ECF)
Cell (ICF)
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Lecture Outcomes
At the end of the session, the student is able to:
describe the compartments of body fluids describe how various volumes of body fluids can be
determined
list the composition of body fluids explain the disturbances in water distribution under
various conditions
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Body Fluid Compartment
Total Body Water;
60% (42L)
Intracelluar Fluid , ICF
40% (28L)
Extracellular Fluid, ECF
20% (14L)
Plasma (3L)
Interstitial fluid (11L)
Transcellular
(1L)RBC (2L)
Total Blood
Volume (5L)
8% body wt 4
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Body Water
1. Gender:
: 60% of body weight
: 55% of body weight
Total Body Water volume depends on
2. Age:
infants > adults > old age
increase in fat content, decrease in in ECF and/ or ICF ?
3. Fat content:
more fat content , less water
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Separation of ICF from ECF
cell membrane semi permeable membrane
ICF and ECF compositions are different
free water movement between ICF and ECF(aquaporins present in cell membrane)
osmolarity ICF = ECF = 300 mOsm/L Changes in ECF osmolarity (osmotic pressure
difference) followed by water movement(osmosis) until new equilibrium reached
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Separation of Interstitial Fluid from Plasma
Capillary endothelium permeable to water andelectrolytes but not to proteins
major difference in protein concentration
oncotic pressure difference
Major determinants of fluid movement frominterstitial space and capillary :
hydrostatic pressure
capillary oncotic pressure
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Composition of ICF and ECF
Composition ICF
mmol/l
Interstitial fluid
mmol/l
Plasma
mmol/l
Na+ 12 145 142
K+ 150 4.4 4.3
Ca 2+ 4.0 2.4 2.5Mg 2+ 34 1.1 1.1
Cl- 4.0 117 104
PO42- 40 2.0 2.0
Prot- 54 0 14
HCO3- 12 27 24
E C F
pH 7.1 7.4 7.4
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Measurement of body Fluidcompartments
dye dilution technique
Principle
concentration = Mass of a substance
volume
Volume = Mass of a substance
Concentration
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1. Known amount of Dye X putinto container B with unknownvolume
Volume container B = Amount of dye XConc X
a
Principle: Concentration= Amount of substancevolume
B
X
2. Dye X mixes in the fluidcontained in container B and reachesequilibrium
Conc Xa
= Amount of dye XVolume B
B
Xa
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Properties of dye that can be used
1. For a certain compartment; dye has to remain in thespecific compartment
2. Non-toxic
3. Distributes evenly in the specific compartment4. Can be measured
5. Neither synthesized nor metabolized by body
6. Does not influence the distribution of water or othersolutes within the compartment
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1. Total body water (TBW)
Dye has to distribute evenly within all thecompartments; ECF and ICF
Dye must cross cell membrane
e.g: deuterium oxide (2H2O), tritiated water (3H2O),
antipyrine
Dye/indicator for various compartments
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2. Total ECF
Dye has to distribute evenly within ECF, interstitiumand plasma
Dye cannot cross the cell membrane
e.g: inulin
sucrose
radioactive isotope (36 Cl, 85Br, 23Na)
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Thus, what is measured is not the true ECF so it is conventional torefer to the compartment measured not as ECF but as a spacedefined by the tracer used and the equilibration time (eg 20 hourbromide space).
The crystalloids are larger and less diffusablethroughout the ECF. They do not enter cells but thelack of full ECF distribution results in
underestimation of ECF.
The ionic tracers are small and distribute throughout the ECFbut there is some entry into cells. ECF will be over-estimated
with these tracers
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3. ICF
Cannot be measured directly
ICF = TBW - ECF
4. Interstitial fluid
cannot be measured directly
There is no tracer which are distributed only throughout thiscompartment. ISF is determined indirectly as the difference between
concurrently measured ECF & plasma volumes.
Interstitial fluid = ECF - plasma
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There is no substance available so ICF is measured indirectly as thedifference between concurrently measured total body water and ECF.The volume of ICF decrease with increasing age and this may accountfor the age-related decline in total body water.
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4. Plasma
Indicator should not leave blood vessel
Indicator should not cross into the RBC
e.g: Evans Blue; binds to albumin
Or radioactive serum albumin (RISA)
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Indicator should beconfined to plasmain blood vessel
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5. Total blood volume
Calculated from plasma volume
Total blood vol = plasma vol X 100100-Hct
RBC Vol = Total blood vol Plasma vol
Or can determine directly; using RBC tagged withradioactive compound (radio-chromium; 51Cr-red cells)
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Summary of Indicators
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Body Fluid disturbances
Changes in water and solutes with externalenvironment occur through ECF
Changes in ICF secondary to changes in ECF
Fluid shifts from ICF to ECF and vice-versa when
osmolarity of ECF is perturbed
ICF and ECF always in osmotic equilibrium plasma osmolarity gives a measure of ICF osmolarity
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Fluid shifts between ICF & ECF andECF & plasma
Knowledge of fluid shifts can be used to understandthe disturbances that can occur when fluid is lost frombody or added to body
Fluid shifts depend on the type of fluid lost or added tobody
It can be used as a basis for treatment of fluiddisturbances
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Disturbances in Body Fluid
Initial disturbance occurs in ECF
Volume : contraction : expansion
Osmolarity : Isotonic
: Hypotonic: HypertonicChanges in ECF osmolarity will shift the ICF
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Expansion
Contraction
Isotonic
Hypotonic
Hypertonic
Body Fluid Disturbances
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C diti EXPANSION ECF ECF ICF ICF
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Condition EXPANSION ECFvol
ECFOsm
ICFvol
ICFOsm
Add isotonic solution (isotonic expansion) Add hypertonic solution (hypertonic
expansion) e.g.
Add hypotonic solution (hypotonicexpansion) e.g. excessive drinking of water,syndrome of inappropriate ADH secretion(SIADH)
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Condition CONTRACTION ECF ECF ICF ICF
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Condition CONTRACTION ECFvol
ECFOsm
ICFvol
ICFOsm
Lose isotonic solution (isotonic contraction)e.g vomiting, diarrhoea, haemorrhage
Lose hypotonic solution (hypertoniccontraction) e.g excessive sweating,diabetes insipidus
Lose hypertonic solution (hypotoniccontraction) e. Addisons disease
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Body responds to the body fluid disturbances
Normally:
disturbance is temporary
body responds to reduce disturbance
Mechanisms:
1. Water intake
2. Urine excretion
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Examples for body fluid disturbance:
1. Excessive sweating: hypertonic contraction
Response: thirst sensation
decrease urine excretion
2. Drink large volumes of water: hypotonic expansion
Response: increase urine excretion
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Clinical setting:Treatment regiment based on patients needsIntravenous solutions are available in many formulations
To increase vascular volume:use solution containing substances that do notcross capillary membrane (e.g. 5% albumin)
To increase ECF volume:use isotonic solutions (e.g. 0.9% NaCl)
To decrease the osmolality of body fluid:use hypotonic solutions (hypotonic NaCl e.g0.45% NaCl or 5% dextrose in water)
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To increase osmolality of body fluid:use hypertonic solutions (e.g. 3% NaCl)