DR. ZAHOOR ALI SHAIKH
Lecture--5
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Human Body Composition:
Water ---- 60%
Protein --- 18%
Fat -------- 15%
Mineral --- 07 %
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Body water makes 60% of body weight.
 Therefore body water is about 42 liters in 70
kg person.
 Body water is distributed between TWO
major compartments:
1. INTRACELLULAR FLUID (ICF)
2. EXTRACELLULAR FLUID (ECF)
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We will see how this 42 liters of water is
distributed between ICF and ECF
Total Body Water (TBW)--- 42 liters
- Intracellular fluid (ICF)----- 28 liters
- Extracellular fluid(ECF)-----14 liters
( ECF IS DIVIDED INTO INTERSTITIAL FLUID
AND PLASMA ).
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Extracellular fluid (ECF)- 14 lit is divided into:
- Interstitial fluid --- 11 liters
- Plasma -------------- 3 liters
 Note--
Interstitial fluid is the fluid which is
distributed between the cells or surrounding
the cells.
Plasma – It is fluid portion of blood.
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 SUMMARY
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TOTAL BODY WATER (TBW) – 42 liters
- Intracellular fluid – 28 liters
- Extracellular fluid – 14 liters
(i). Interstitial fluid – 11 liters
(ii). Plasma - 3 liters
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
There are other TWO Minor Extracellular fluid
compartments also:
1. Lymph
2. Transcellular fluid
1. Lymph
It is fluid which is returned from the
interstitial fluid to plasma by means of
Lymphatic System.
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2. Transcellular Fluid
It is small fluid volume secreted by specific cells
in the body, these cells perform special function
 Example of Transcellular fluid
- Cerebrospinal fluid (CSF)- it surrounds the
Brain and Spinal cord
- Intra ocular fluid - in the eye
- Synovial fluid – lubricating joints
- Pericardial fluid, Intra pleural fluid
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Plasma and Interstitial Fluid are separated by
blood vessel wall.
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Water and electrolyte are freely exchanged
between plasma and interstitial fluid
passively through pores of thin capillary
membrane.
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But Plasma protein can not pass from plasma
to interstitial fluid.
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Therefore plasma and interstitial fluid are
nearly same in composition except that
plasma has protein and interstitial fluid
doesn’t have protein.
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ECF and ICF are separated by plasma
membrane.
Plasma membrane is selectively permeable.
There is passive transport and active
transport occurring through the plasma
membrane.
There is difference between ECF and ICF.
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INTRACELLULAR FLUID [ICF]
EXTRACELLULAR FLUID [ECF]
1. ICF has more protein
1. No protein in Interstitial Fluid.
Protein present in Plasma.
2. More Potassium ion
(145 mmol / l)
2. Less Potassium ion
(4 mmol / l)
3. Less Sodium ion
(10 mmol / l)
3. More Sodium ion
(145 mmol / l)
4. More Phosphate ion
4. More Chloride ion
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Q. Why Na+ is more in ECF and K+ more in ICF?
Ans: It is due to the Na+ - K+ ATPase pump
which pumps Na+ outside the cell and K+
inside the cell.
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Both Interstitial Fluid and Plasma have same
composition except that Plasma has more
protein.
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ICF and ECF are different as plasma
membrane is selectively permeable and
Na+ - K+ ATPase pump is operating.
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ECF
Na+ 140 mmol / l (135-145 mmol / l)
K+
4 mmol / l (3.5 – 5 mmol / l)
Cl-
105 mmol / l (100 – 110 mmol / l)
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Fluid Balance is regulated by:
1- ECF Volume
2- ECF Osmolarity
- ECF volume helps to maintain blood
pressure and will be discussed later with
blood pressure.
We will discuss ECF Osmolarity.
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What is Osmolarity ?
Osmolarity is the concentration of solute
particles dissolved in the fluid.
Increased Osmolarity means higher
concentration of solute and less
concentration of water.
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As Na+ is the main solute in ECF, it is
responsible for ECF Osmolarity.
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In ICF K+ is responsible for ICF Osmolarity.
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Normally ECF and ICF are ISOTONIC (having
same Osmolarity).
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Normally Osmolarity of ECF and ICF are the
same (they are isotonic).
 Why ?
 Because total concentration of Na+ and other
solutes in ECF is equal to total concentration
of K+ and other solutes inside the cell.
 Remember
Osmolarity of ECF - 285 mmol/l (275 – 295)
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
PROBLEM
 If there is water loss from the ECF , what will
be its effect ?
Answer – ECF will become Hypertonic.
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ECF will become hypertonic if water is lost
from it e.g. diarrhea, vomiting, sweating or
less water intake.
If ECF becomes more hypertonic, water
moves from the cells into ECF by osmosis
(i.e. from ICF to ECF).
As water leaves the cell – cell will shrink.
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
In mild Dehydration (loss of water) and mild
hyper tonicity --- There is dry skin, dry tongue
thirst, sunken eyes.
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In case of severe Hyper tonicity ( Hyper
Osmolarity) of ECF, it may affect BRAIN
CELLS and BRAIN FUNCTION --- person may
become mentally confused.
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 PROBLEM
 What will happen if ECF becomes Hypotonic
(that is having less Osmolarity) ?
 Answer – When ECF becomes Hypotonic , water
will enter the cell, and cell will swell ( get bigger).
 NOTE – Usually Hypo tonicity does not occur
because when we take more water, we loose
water in urine, but it can happen in Abnormal
conditions.
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In Renal failure, patient can not pass urine ,
therefore ECF will become hypotonic if water is
added to it.
When ECF becomes hypotonic, water will enter
into the cell by Osmosis and cells will swell
(increase in size).
Swelling of BRAIN cells will cause Brain
Dysfunction E.g. – headache, vomiting,
confusion, drowsiness and coma. This is called
WATER INTOXICATION.
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 What will happen if we give Is0tonic solution?
 Answer – If we give ISOTONIC SOLUTION
like o.9% saline (Isotonic saline)
intravenously, ECF will remain ISOTONIC ,
there will be no net movement of water into
or out of the cells. Only ECF volume will
increase.
 NOTE – In case of
Diarrhea, vomiting ,
Isotonic saline is given intravenously .
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Distribution of Body water – ICF, ECF
[Interstitial Fluid in Plasma]
Define Tran cellular Fluid
Compare Ionic composition of Plasma,
Interstitial Fluid and Intracellular Fluid
What is Osmolarity of Plasma?
Define Isotonic, Hypotonic, Hypertonic
What are causes of ECF hyper tonicity and
hypo tonicity and its effects on body?
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