4. body fluids medical 1011

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)

4. body fluids medical 1011

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