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FLUID BALANCE
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FLUID BALANCE
The Balance Concept: Input -Output =Storage/Depletion
Body Fluid CompartmentsRegulation of fluid balance
Relation between Salt Balance and ECF
Volume
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Input -Output =
Storage/Depletion
InternalPool (ECF
Concentration)
of substance
Storage
Metabolic
Production
Metabolic
Consumption
Inside
Body
Inputs from
environment
Excretion
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Body Fluid Compartments
Compartment Fluid Vol.(l)
% Body Fluid
% Body Wgt.
Total Body
Fluid42 100 60
IntracellularFluid(ICF)
28 67 40
ExtracellularFluid (ECF)
14 33 20
Plasma 2.8 6.6
(20% ECF)
4
Interstitial Fluid
11.2 26.4(80% ECF)
16
Lymph &
Transcellular Fluid
Neg. Neg. Neg.
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BODY FLUID COMPARTMENT
COMPOSITION
Plasma Interstitial
Fluid
Intracellular
Fluid
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Regulation of fluid balance
ECF Volume: Maintains blood pressure
ECF Osmolarity: Prevents swelling orshrinking of cells
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ECF Volume: Maintains
blood pressure - Short Term
A Change in ECF Volume can raise orlower blood pressure
Barorecepter reflexes: Alter Cardiacoutput and Total Peripheral Resistanceleading to a compensatory alteration in
blood pressureFluid automatically shifts between plasma
and interstitial fluid with rises or fall in
blood pressure
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Relation between Salt
Balance and ECF Volume
The total sodium load (quantity of sodium, not its concentration) in the ECF
determines the total amount of waterthat will be osmotically retained
The total sodium load is determined by
the balance relation
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Input -Output =
Storage/Depletion
InternalPool (ECF
Concentration)
of substance
Storage
Metabolic
Production
Metabolic
Consumption
Inside
Body
Inputs from
environment
Excretion
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Control of sodium load
Control of amount filtered by regulatingGFR (Glomerular Filtration Rate)
Control of sodium reabsorption throughthe Renin-Angiotensin-Aldosterone system
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ECF Osmolarity: Prevents swelling or
shrinking of cells
ECF hypertonicity is associated withdehydration
ECF hypotonicity is associated withoverhydration
Control of water balance is by thirst andvasopressin
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Blood pressure and renal
handling of sodium
FALL IN SODIUM LOAD
FALL IN ARTERIAL PRESSURE
FALL IN GFR
FALL IN FILTERED
SODIUM
INCREASE INALDOSTERONE
SECRETION
INCREASE IN
SODIUM
ABSORPTION
FALL IN EXCRETION OF
SODIUM, CHLORIDE, AND
FLUID
INCREASED CONSERVATION
OF SODIUM AND FLUID
RELIEVES
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DAILY WATER BALANCE
(LITERS)
FLUID INTAKE 1.25
IN FOOD 1.0
METABOLIC 0.35
INSENSIBLE 0.9
SWEAT 0.1
FECES 0.1
URINE 1.5TOTAL 2.6
INPUT (ml/day) OUTPUT (ml/day)
TOTAL 2.6
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WATER DEFICIT
INCREASED OSMOLARITY SENSED BY HYPOTHALAMIC WATER RECEPTORS
FALL IN ECF VOLUME
FALL IN ARTERIAL BLOOD PRESSURE
STIMULATIONOF HYPOYHALAMIC
NEURONS
INCREASED THIRST
INCREASED WATER INTAKE
DECREASED PLASMA OSMOLARITY
INCREASED VASOPRESSIN
OPEN PORES
IN COLLECTING
DUCT
MORE WATER REABSORBED
FALL IN URINE OUTPUT
ARTERIOLAR
VASOCONSTRICTION
DECREASED PLASMA OSMOLARITY
RELIEVES
RELIEVES
