3. Introduction
• Water is so familiar and so large a constituent of the body that its
fundamental importance in both structure and functioning of all tissues
tends to be overlooked.
• Water is the most essential constituent of our body. It accounts for 55-70 %
of our total body weight. Men have a higher proportion of water in their body
as compared to women. Lean individuals have more water than the obese,
and infants and children have a greater proportion of water than adults. The
total body fluid is distributed among two major compartments:
– 1. The extracellular fluid or water present outside the cells in the interstitial
spaces and blood plasma
– 2. The intracellular fluid or the water present inside the cells
• Considering an average of 60 per cent of body weight contributed by water,
an adult weighing 70 kg has a total body water of 42 litres of which 28 litres
is intracellular and 14 litres is extracellular. Of the 14 litres, 11 litres is
present as interstitial fluid and 3 litres as plasma. Water present in the body
is never plain water but has electrolytes dissolved in it. Similarly, when the
body loses water, it loses electrolytes as well.
4. Functions
• 1. Water quenches thirst and is the most refreshing and
cooling of all liquids.
• 2. It is a structural component of all cells. In the bone,
water is tightly bound, but in most tissues, a constant
interchange takes place between the body
compartments of water.
• 3. Water is the medium in which all chemical reactions
take place.
• 4. It is an essential component of all body fluids such as
blood, lymph, cerebrospinal fluid, bile, digestive juices,
and urine.
5. Functions
• 5. It acts as a lubricant and helps food to be swallowed
and digested food to pass through the gastro-intestinal
tract.
• 6. It acts as a solvent for the products of digestion and
helps in transporting these products to different tissues.
• 7. Water regulates body temperature by 'taking up and
distributing heat produced in cells when metabolic
reactions take place.
• 8. It helps in excreting waste products of metabolic
reactions.
• 9. Water is essential to maintain the turgidity of cells.
