- Water makes up 60-70% of the human body and plays several important roles like acting as a solvent, transport medium, lubricant, and participating in chemical reactions.
- Water and electrolytes like sodium, potassium, and chloride are distributed between intracellular and extracellular fluid compartments, with water moving between compartments down its osmotic gradient.
- The body tightly regulates water and electrolyte balance through mechanisms like the renin-angiotensin-aldosterone system, antidiuretic hormone, atrial natriuretic factor, hypothalamic centers, and kidney function. Imbalances can lead to disorders.
2. Water is a universal solvent & the most essential
component of life
Imp nutrient &It’s prime role is in maintaining life.
About 60 – 70% of the adult human body is constituted
by water
Since fat is water insoluble, water content of the body
alters. In obese people water content is low
Females have a low water content because of a relatively
high % of fat
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
3. It is a medium in which body solutes are dissolved &
metabolic reactions take place
Involved in regulation of body temperature
(because of its highest latent heat of evaporation)
Acts as a vehicle for transport of
solutes
Acts as a lubricant in the body so as to prevent friction in joints,
pleura, peritoneum & conjunctiva
Functions Of Water
4. Water itself participates as
a substrate, Involve in
many chemical reactions
(e.g. in glycolysis, TCA
cycle & respiratory chain)
The stability of sub
cellular structures
&activities of numerous
enzymes are dependant
on adequate cell
hydration
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
6. Intra Cellular Fluid (ICF) -
40%
Extra cellular fluid (ECF) -
20%
Intravascular fluid,
i.e. blood plasma
(within blood vessels)- 4%
Constitutes the medium in
which chemical reactions of
cell metabolism occurs
Fluid found outside the cells
Extravascular fluid,
i.e. interstitial fluid
(speces b/w cells)- 16%
Total body Water (60%)
Fluid found within the cell
Constitutes the medium through,
which all metabolic exchange
occurs
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
7. Colloidal osmotic pressure
Two factors influence the distribution of water between
intra cellular & extracellular compartments
Osmolality
8. no. of moles per kg of solvent, irrespective of the size, or
nature of the particles
Water diffuses from a compartment of low to high
Osmolality unit
Units of Osmolality are mmol/ kg of water. conc. is
expressed as osmoles per liter of solution – osmolarity
This affects the movement of water across the
cell membranes
Osmolality
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
9. Colloidal Osmotic Pressure (COP)
• COP that determines the distribution of water among body water
compartments.
• Osmotic pressure of a solution is proportional to it’s osmolality.
• A solution with an osmotic pressure greater than plasma called
hypertonic or hyper osmotic.
• COP exerted by the plasma proteins- oncotic pressure
• Hydrostatic pressure & oncotic pressure affects the movement of
water &low mol mass solutes between IV & EV compartments
12. • Substances which readily dissociate in the solutions and
exist as ions - Electrolytes.
NaCl Na+ + Cl-
• Conc. of individual electrolytes is expressed as mEq/L
not mg/L
• mEq/L is the ion conc. in millimoles, multiplied by the
number of electrical charges on the ion
• These are distributed among body fluids, which maintain
osmotic equilibrium and water balance.
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
13. Maintain membrane
potential
Participate in muscle
contractions Involved in blood clotting
process, enzyme action
Involve gas transport
mechanism
Nerve impulse conduction
Electrolytes Functions
exert the greatest influence on
water balance & acid base
balance.
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
16. Renin angiotensin- Aldosterone system
(RAAS)
Antidiuretic hormone or vasopressin (ADH)
Hypothalamic mechanism controlling Thirst
Atrial natriuretic factor (ANF)
Kidneys
Occurs together which
depends on
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
17. When water & Na+ output exceed intake
↓
ECF volume contracts
↓
Associated decrease in plasma volume
↓
Decrease in cardiac output
Stimulation
of water
intake area of
the
hypothalamus
& thirst
center
Stimulation
of H2O
output area of
the
hypothalamus
& ADH
secretion
Inhibition
of release of
ANF
Retention
of
Na+ &
H2O
by
kidneys
Stimulation
of
RAAS
18. Hypothalamus Mechanism
• Regulation areas of water intake & output are located in separate
areas of hypothalamus in brain.
• Both water & electrolyte balance are regulated together through
» ADH (Vasopressin)
» RAAS (Renin angiotensin- Aldosterone system )
» ANF (Atrial natriuretic factor )
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
19. Antidiuretic Hormones
Water intake is
controlled by the
sensation of thirst & its
output by the action of
hormone ADH
+
Hypothalamic
thirst center
Hypothalamic
posterior pituitary
Increase in plasma osmolality
+
↑Thirst
↑water intake
↑Secretion of ADH
↑Water reabsorption
by kidney
Restored plasma osmolality
Deficiency of water
+
+
Large intake of water
causes fall in osmolality
suppresses thirst & reduces
ADH secretion, leads to
diuresis, producing large
volume of dilute urine .
20. Renin –angiotensin system:
• Secretion of aldosterone is regulated by the RAS, when there is
a fall in ECF volume renal plasma flows decrease.
• This would be sensed by the juxtra glomerular apparatus of the
nephrons, which secret renin.
Stimulating the release of
renin
Inhibits the release of
renin
- Decreased blood volume
- Salt depletion
- Prostaglandins stimulators
- Increased blood pressure
- High salt intake
- Prostaglandin inhibitors
- Angiotensin-II
Santhosh Kumar .N/ Dept.of Biochem/ SIMS&RH
22. Atrial Natriuretic factor (ANF)
• It is a polypeptide hormone secreted by the right atrium of
the heart
• They inhibit renin & aldosterone secretion & eliminate Na+
• Involve in the control of Na+ & water balance.
• Net results of all these effects water & Na+ balance become
+Ve & ECW is restored to normal
