Dr. Rida Shabbir
DPT KMU
Normal
Intake:
 Fluids ingested
(Drinking/in food)
 From metabolism
2100
200
Prolonged, heavy exercise
?
200
Total intake
2300ml/d
Output:
 Insensible – skin
 Insensible – lungs
 Sweat
 Feces
 Urine
350
350
100
100
1400
350
650
5000
100
500
Total output
2300
6600
In steady state, water intake = water loss
?
Extracellular fluid
( 1/3)
14 L
 20% of body wt
Plasma
3L
 25% of ECF
 5% of body wt
Interstitial fluid
11 L
75% of ECF
 15% of body wt
Intracellular fluid
( 2/3)
28 L
 40% of body wt
Transcellular fluid
CSF
Intraocular
Pleural
Peritoneal
Pericardial
Synovial
Digestive
secretions
Water intake & output
 Age:
- infant: 73%
- elderly: 45%
 Sex:
- adult male: 60%
- adult female: 40-50%
 Obesity
 Climate
 Habits
 Level of physical activity

 Contains
both extracellular and intracellular
fluid.
 Separate fluid compartment in its own
chamber.
 Average 7% of body weight or 5 L.
 60% is plasma and 40% is cell.
 True hematocrit is 96% of measured
hematocrit.
The extracellular fluid, including
the plasma and the interstitial
fluid, contains large amounts of
sodium and chloride ions,
reasonably large amounts of
bicarbonate ions, but only small
quantities of:
• potassium
• Calcium
• Magnesium
• Phosphate
• organic acid ions.
 Because
the plasma and interstitial fluid are
separated only by highly permeable capillary
membranes, their ionic composition is
similar.
 Higher concentration of protein in the
plasma.
 Small amounts of proteins are leaked into
the interstitial spaces in most tissues

Because of the Donnan effect, the concentration of
positively charged ions (cations) is slightly greater
(about 2 per cent) in the plasma than in the
interstitial fluid.

The plasma proteins have a net negative charge
and, therefore, tend to bind cations, such as sodium
and potassium ions, thus holding extra amounts of
these cations in the plasma along with the plasma
proteins.

Conversely, negatively charged ions (anions) tend to
have a slightly higher concentration in the
interstitial fluid compared with the plasma, because
the negative charges of the plasma proteins repel
the negatively charged anions.
 Intracellular
fluid separated from extra cellular
fluid by cell membrane.
 Highly permeable to water but not to most of the
electrolytes.
 Small quantities of sodium and chloride. No
calcium ions.
 Large amount of potassium and phosphate ions.
 Moderate quantities of magnesium and sulphate
ions.
 Large amount of proteins. 4 times that of plasma.
 Evenly
dispersed indicator substance and
accessing dilution.
 Based on conservation of mass principle.
 Total mass of a substance after dispersion in
fluid compartment is same as total mass
injected in the compartment.
 Total mass of the substance in the
compartment (vol B x conc B) = total mass of
the substance injected (vol A x conc A)
 Vol B= vol A x conc A/ conc B
 Measurement



Tritium and deuterium can be used to measure total
body water.
Dilution principle can be used to measure total body
water.
Antipyrine (lipid soluble).
 Measurement



of total body water:
of extracellular fluid volume:
Substances that disperse in plasma and interstitial fluid
but do not readily permeate the cell membrane.
Radioactive sodium, chloride, iothalamate,
thiosulphate ions and inulin.
Injected in blood and disperses in 30-60 mints.
 Calculation

of intracellular volume:
Intracellular vol= total body water – extracellular vol.
 Measurement


Substances that do not cross capillary membrane.
Serum albumin with radioactive iodine.
 Calculation

of interstitial fluid vol:
Interstitial fluid vol= extracellular fluid vol – plasma
vol.
 Measurement

of plasma vol:
of blood vol:
Total blood vol= plasma vol/ 1- hematocrit.