FLUID COMPARTMENTS
EXTRA CELLUAR
FLUID
PLASMA
1.
2.
3.
4.
5.
6.
INTERSTITIAL
FLUID
CSF
Intra ocular
Pleural
Peritoneal
Synovial
Digestive Secretions
INTRA CELLULAR
(cytosol)FLUID
TRANSCELLULAR
FLUID
FACTORS AFFECTING PERCENTAGE OF WATER IN TISSUES
• Age
• Gender
• Degree of body fat
THE EFFECT OF AGE, GENDER AND DEGREE BODY FAT ON
PERCENTAGE OF H2O IN TISSUES
COMPOSITION OF FLUID COMPARTMENT
Major cations and anions of the intracellular and extracellular fluids. The concentrations shown represent the total of free and complexed
ions
The non-electrolytes of the plasma
NOTE:
• The total osmolarity of each of the three compartments is about 300
mOsm/litre
• The plasma is about 1 mOsm/litre greater than that of the ISF &ICF
(due to plasma protein)
• Water moves rapidly across cell membranes, hence the osmolarities
of ICF & ECF fluids remain almost exactly equal to each other
• The cell membrane is almost completely impermeable to many
solutes, therefore the number of osmoles in the ECF or ICF fluid
remains constant unless solutes are added to or lost from the
extracellular compartment
• pH of ECF is 7.4 and ICF 7.0
Measurement of Body Fluid Volume
• Total body water and the volume of different compartments of the
body fluid are measured by STEWART HAMLINTON METHOD
• This works with indicator dilution principle (a known
substance/indicator is injected into the blood and the rate/volume of
dilution is estimated).
• The plasma volume, ECF volume and the total body water (TBW) can
be measured using dilution technique
• The interstitial and intracellular fluid volume are measured indirectly
CRITERIA FOR A SUITABEL DYE.
1. Must mix evenly throughout the compartment of interest
only
2. Non toxic, no physiological activity
3. Must have no effect of its own on the distribution of H2O
or other substances in the body.
4. It must not be metabolized by the body.
5. The material should be relatively easy to measure.
6. It should not be excreted during the period of mixing
 Measurement of Total Body Water
• Can be measured using the dilution technique
• Substances like radioactive water (Tritiated water)(3H2O) or heavy
water (Deuterated) (2H2O) can be used.
Measurement of Plasma Volume
• Can be measured using the dilution technique
• A substance that does not readily penetrate the capillary membrane
is used.
• These include serum albumin labelled with radioactive iodine (125Ialbumin) and Evans blue dye (T-1824)
 Determination Extracellular Fluid Volume
• For extracellular volume, a substance that does not cross cell
membranes, but does pass through capillary pores is used.
• Radioactive sodium (Na24), Radioactive chloride (Cl35), Radioactive
iothalamate (I125), thiosulphate ion and inulin
 Calculation of Intracellular Fluid Volume
• Its measured indirectly by first determining total body water (TBW)
and extracellular fluid (ECF) volume
• Calculated mathematically as the difference of total body water and
Extracellular fluid water
ICF = TBW – ECF volume
Calculation of Interstitial Fluid Volume
• Also measured indirectly
• Calculated mathematically as:
ISF = ECF – Plasma volume
Contribution of Body Fluid to Homeostasis
• 1. maintenance of body osmolality within narrow limits
• 2. maintenance of ECF and blood volume at adequate levels
• 3. help regulate myocardial and neurological function
• 4. Regulates acid-base balance
FORCES PRODUCING MOVEMENT OF SUBSTANCES
BETWEEN BODY FLUID COMPARTMENT
• Fluid compartments are separated by membranes whose
permeability to various substances vary
• The two components of the ECF—plasma and interstitial fluid—are
separated by the walls of the blood vessels (capillary wall)
• The barrier between the ECF and the ICF is the cellular membrane
that permits passage of certain materials while excluding others
(passive and active movements)
• Movement of fluids due to:
hydrostatic pressure
• osmotic pressure
•
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