• The transport of the substances along the
concentration gradient is called diffusion.
• It is a type of passive transport.
• It is like swimming in the direction of water flow in a
• In this mechanism, the substances are transported
from region of higher concentration to the lower
concentration. Hence, it is also called downhill
5. Simple diffusion
• Diffusion of the substances occurs through lipid layer
or protein layer of the cell membrane.
• Examples : water, gases, pentose sugars.
6. Facilitated diffusion (Carrier mediated diffusion)
• This is a carrier mediated process
• Important features of facilitated diffusion are:
1. The carrier mechanism could be saturated which is similar
to the Vmax of enzymes.
2. Structurally similar solutes can competitively inhibit the
entry of the solutes.
3. Facilitated diffusion can operate bidirectionally.
4. This mechanism does not require energy but the rate of
transport is more rapid than simple diffusion process.
5. The carrier molecules can exist in two conformations,
Ping and Pong states.
7. 6. In the pong state, the active sites are exposed to the
exterior, when the solutes bind to the specific sites.
Then there is a conformational change.
7. In the ping state , the active sites are facing the
interior of the cell , where the concentration of the
solute is minimal.
8. This will cause the release of the solute molecules and
the protein molecule reverts to the pong state.
9. By this mechanism the inward flow is facilitated, but
the outward flow is inhibited.
10. Hormones regulate the number of carrier molecules.
• For example, glucose transport across membrane is by
facilitated diffusion involving a family of glucose
10. Factors affecting diffusion
• Thickness of the cell membrane : Inversely Proportional.
• Permeability of the cell membrane : Directly proportional
• Temperature : Directly proportional
• Concentration Gradient : Directly proportional
• Size of the molecules : Inversely Proportional
• Solubility of the substances : Directly proportional
11. Applications of diffusion
1. Exchange of 02 and CO2 in lungs and in tissues occurs
2. Certain nutrients are absorbed by diffusion in the
gastrointestinal tract e.g. Pentoses , minerals, water
3. Passage of the waste products namely ammonia, in the
renal tubules occurs due to diffusion.
19. Ion Channels
• Ion channels are trans-membrane proteins that allow the
selective entry of various ions. These channels are for
quick transport of electrolytes such as Ca++, K+, Na+ and Cl- .
• These are selective ion conductive pores. Ion channels are
specialized protein molecules that span the membranes.
• The channels generally remain closed, but in response to
stimulus, they open allowing rapid flux of ions down the
20. Features of Ion Channels
1. They are trans membrane proteins
2. Selective for one particular ion
3. Regulation of activity is done by voltage-gated, ligand- gated or
mechanically gated mechanisms
4. Different channels are available for Na+, K+, Ca++ and Cl-
5. Transport through the channel is very quick
6. They are important for nerve impulse propagation, synaptic
transmission and secretion of biologically active substances from
21. Ligand Gated Channels
• Ligand gated channels are opened by binding of
• The binding of a ligand to a receptor site on the channel
results in the opening (or closing) of the channel.
• The ligand may be an extracellular signalling molecule or
an intracellular messenger.
23. • Acetyl choline receptor is the best
example for ligand gated ion channel.
• It is present in postsynaptic membrane.
• It is a complex of 5 subunits, consisting
of acetyl choline binding site and the
• Acetyl choline released from the
presynaptic region binds with the
receptors on the postsynaptic region,
which triggers opening of the channel
and influx of Na+.
• This generates an action potential in
the postsynaptic nerve.
• Calcium channels:
• It is an example of voltage gated
• Under appropriate stimuli calcium
channels are opened in the
sarcoplasmic reticulum membrane,
leading to an elevated calcium level in
the cytosol of muscle cells.
24. Voltage Gated Channels
• Voltage gated channels are opened by membrane
• The channel is usually closed in the ground state.
• The membrane potential change (voltage difference)
switches the ion channel to open, lasting less than 25
• They are membrane shuttles for specific ions.
• They transport antibiotics.
• Ionophores increase the permeability of membrane
to ions by acting as channel formers.
• The two types of ionophores are;
• Mobile ion carriers and channel formers.
• They are a family of
membrane channel proteins
through which water
crosses the plasma
membranes of cells.
• They control the water
content of cells.
• Diabetes insipidus is due to
impaired function of these
27. Active Transport
• This form of transport requires energy.
• It requires specialized integral proteins called
• The transport system is saturated at higher
concentrations of solutes.
• The transporters are susceptible to inhibition by
specific organic or inorganic compounds.
32. ABC transporters
• It constitute a large family of ATP-dependent
transporters that pump amino acids, peptides,
proteins, metal ions, various lipids, bile salts, and
many hydrophobic compounds, including drugs,
out of cells against a concentration gradient.
• One ABC transporter in humans, the multi-drug
transporter (MDR1), is responsible for the
resistance of certain tumors to some generally
effective antitumor drugs.
33. Sodium Pump
• Low intracellular sodium; and high potassium inside the
cell is maintained by the sodium–potassium activated
ATPase, generally called as sodium pump.
• It is an integral protein of the membrane having binding
sites for ATP and sodium on the inner side and the
potassium binding site on outside the membrane.
• It is made up of two pairs of unequal subunits α2 β2. Both
subunits of the pump (alpha and beta) span the whole
thickness of membrane.
34. Fig. Ion channel Fig. Active transport
BLACK CIRCLE = SODIUM ION; GREEN SQUARE =POTASSIUM ION; PINK CIRCLE = PHOSPHATE.
(1) Cytoplasmic Na+ (3 numbers) bind to the channel protein.
This favors phosphorylation of the protein along with hydrolysis of ATP.
(2) Phosphorylation causes the protein to change conformation, expelling the Na+ across the
(3) Simultaneously, extracellular K+ (2 numbers) move to the carrier protein. Potassium binding
leads to release of phosphate group.
(4) Original conformation is restored.
(5) K+ are released into the cytoplasm. The cycle repeats
Fig. The sodium potassium pump
35. Calcium Pump
• It regulates muscle contraction.
• A specialized membrane system called sarcoplasmic reticulum
regulates the Ca++ concentration around muscle fibers.
• In resting muscle the concentration of Ca++ around muscle fibers is
low. But stimulation by a nerve impulse results in a sudden release of
large amounts of Ca++which would trigger muscle contraction.
• The function of calcium pump is to remove cytosolic calcium and
maintain low cytosolic concentration, so that muscle can receive the
next signal. Each ATP hydrolysed, 2Ca++ ions are transported.
36. TRANSPORT BY GROUP TRANSLOCATION
• It involves the modification of molecules to be
transported across the membranes
• Transport of aminoacid by gama glutamyl
cycle(Meister cycle) in nephron and small
• It is defined as the flow of water or any other solvent from a
compartment (solution) in which the concentration of solute
is lower to another compartment in which the solute
concentration is higher through a semipermeable membrane
(Permeable to the solvent, but not the solute).
40. Osmotic pressure
• Osmotic pressure may be defined as the excess
pressure that must be applied to a solution to
prevent the passage of solvent into another solution
, when both are separated by a Semipermeable
41. Applications of osmosis
1. Fluid balance and blood volume :
The fluid balance of the different compartments of the
body , regulation of blood volume and urine excretion. is
maintained due to osmosis .
2. Red blood cells and fragility :
When RBC are suspended in an isotonic (O.9% NaCl)
Solution , the cell volume remains unchanged and they are
In hypertonic solution (say 1.5% NaCl), water flows out of
RBC and the cytoplasm shrinks,a phenomenon referred to
42. • When the RBC are kept in hypotonic solution (say O.4%
NaCl), the cells bulge due to entry of water often causing
rupture of plasma membrane of RBC (hemolysis).
• Osmotic fragility test of RBC is employed in Iaboratories
for diagnostic purposes.
• For a normal human blood, RBC begin to hemolyse in
0.45% NaCl and the hemolysis is almost complete in
• lncreased fragility of RBC is observed in hemolytic
jaundice while it is decreased in certain anemias.
43. Applications of osmosis
3. Transfusion :
lsotonic solutions of NaCl(O.9%)or glucose( 5%)or a suitable
combination of these two are commonly used in hospitals
for the treatment of dehydration, burns etc.
5. Osmotic diuresis :
High blood glucose concentration causes osmotic diuresis
resulting in the loss of water, electrolytes and glucose in the
This is the basis of polyuria observed in diabetes mellitus.
44. Applications of osmosis
6. Edema due to hypoalbuminemia :
Disorders such as kwashiorkor and glomerulonephritis
are associated with lowered plasma albumin
concentration and edema.
Edema is caused by reduced oncotic pressure of plasma,
leading to the accumulation of excess fluid in tissue
45. Importance of Osmosis
• Osmosis is essential in biological systems, as biological
membranes are semipermeable
• In general, these membranes are impermeable to large
and polar molecules, such as ions, proteins, and polysaccharides,
while being permeable to non-polar and/or hydrophobic molecules
like lipids as well as to small molecules like oxygen, carbon dioxide,
nitrogen, nitric oxide, etc.
• Entry of water in to the roots from the soil takes place by this
• Cell to cell diffusion of water is controlled through this process.
• Young cells require favorablle condition for their growth which is
fulfilled by osmosis.
46. Reverse osmosis
• The osmosis process can be driven in reverse with
solvent moving from a region of high solute
concentration to a region of low solute concentration
by applying a pressure in excess of the osmotic
51. Method of purification
• The water to be purified is placed in a chamber
and put under an amount of pressure greater than
the osmotic pressure exerted by the water and the
solutes dissolved in it.
• Part of the chamber opens to a differentially
permeable membrane that lets water molecules
through, but not the solute particles.
52. 2. Plant functions
• Osmotic pressure is necessary for many plant
• It is the resulting turgor pressure on the cell
wall that allows herbaceous plants to stand
upright, and how plants regulate the aperture
of their stomata.
53. 3. Cytolysis
• In animal cells which lack a cell wall however,
excessive osmotic pressure can result in
54. COLLOIDAL STATE
• Colloids are mixtures whose particles are
larger than the size of a molecule but smaller
than particles that can be seen with the naked
55. • Thomas Graham (1861), regarded as the
‘father of colloidal chemistry', divided
substances into two classes-
• Crystalloids and
56. • Crystalloids are the substances which in solution
can freely pass (diffuse) through parchment
• e.g. sugar, urea, NaCl.
• Colloids (Creek : glue-like), on other hand, are the
substances that are retained by parchment
• e.g. gum, gelatin, albumin.
57. COLLOIDAL STATE
• As such, there are no group of substances as
colloids, rather, substances can exist in the form
of colloidal state or colloidal system.
• Colloidal state is characterized by the particle size
of 1 to 100 nm.
• When the particle size is <1 nm, it is in true
• For the particle sizes >100 nm, the matter exists
as a visible precipitate.
• The colloidal state is an intermediate between
true solution and precipitate
59. PHASES OF COLLOIDS
1. Dispersed phase (internal phase) which
constitutes the colloidal particles.
2. Dispersion medium (external phase)which
refers to the medium in which the colloidal
particles are suspended
60. Types of colloids
• Colloids can be made from almost any
combination of gas, liquid, and solid.
• The particles of which the colloid is made are
called the dispersed material.
• Any colloid consisting of a solid dispersed in a
gas is called a smoke.
• A liquid dispersed in a gas is referred to as a
• Based on the affinity of dispersion medium
with dispersed phase, colloids are classified as
• lyophobic and lyophilic .
1. Lyophobic (Creek: solvent-hating:)
These colloids do not have any attraction
towards dispersion medium.
When water is used as dispersion medium,
the colloids are referred to as hydrophobic.
62. 2. Lyophilic (Creek : solvent-loving):
These colloids have distinct affinity towards
The term hydrophilic is used for the colloids when
water is the dispersion medium
Dispersed in Gas Dispersed in Liquid Dispersed in Solid
Foams: soda pop; whipped
cream; beaten egg whites
Solid foams: plaster
Fogs: clouds; hair
Emulsions: milk; blood;
Sols and gels: gelatin;
muddy water; starch
Solid sol: pearl; colored
64. Properties of colloids
• A suspension always settles out after a certain
period of time. That is, the particles that make up
the suspension separate from the medium in which
they are suspended and fall to the bottom of a
• In contrast, colloidal particles typically do not settle
out like the particles in a solution, they remain in
suspension within the medium that contain them
65. Importance of colloids
• 1. Colloids in biology
• An important role in the secretion of the
biochemicals from different parts of the body.
• Examples : Thyroid gland and pituitary gland
contain colloid follicles.
• 2. Colloids in the environment
• Serve as transport vector of diverse contaminants in
the surface water and in underground water
circulating in fissured rocks (limestone, sandstone,
66. • Use in intravenous therapy
• Colloid solutions used in intravenous therapy .
• Colloids preserve a high colloid osmotic pressure
in the blood and therefore, they increase the
intravascular volume, whereas other types of
volume expanders called crystalloids also
increases the interstitial volume and intracellular
67. • Osmotic pressure:-
• Colloids exert osmotic(oncotic pressure).
• Plasma osmotic pressure is responsible for
distribution of water between plasma and
68. • Non-permeability(Non-diffusible nature) :-
• This property of colloids contributes to
• Dialysis and donnan membrane equalibrium
• Formation of urine and CSF
• Purification of protein
• Tyndall effect:- It is a light scattering property
• Colloids exert tyndall effect which contributes for
the detection of colloid particle by electron
69. • Charge property:-
• Colloids exist as a charged molecules which
account for the precipitation of proteins by
acids and heavy metals and buffering action
• Salting in:
• Presence of electrolyte ions increase the
stability of solution.
• This is found in increased solubility of
lactglobulin and ovoalbumin in dilute NaCl
70. • Coagulation:
• It is the process in which the separation of
disperse phase particles takes place from the
dispersion medium of the solution.
• It can be caused by freezing, heating, mechanical
agitation, ultrasounds, electromagnetic fields,
radiations or electrolytes.
• Coagulation due to electrolytes is called salting
out and requires higher ionic strength for
lyophilic than for lyophobic solutions.
• Salting out of proteins by ammonium sulphate
71. • Donnan membrane equilibrium :
• The presence of non-diffusible colloidal particles
(e.g. protein) in the biological systems
influences the concentration of diffusible ions
across the membrane.
• Water of hydration:- proteins are kept in
solution because of water of hydration such
colloids are called lyophilic colloids
72. Biological importance of colloids
1. Biological fluids as colloids : These
include blood, milk and cerebrospinal fluid.
2. Biological compounds as colloidal particles
The complex molecules of life, the high
molecular weight proteins, complex lipids
and polysaccharides exist in colloidal state.
73. 3. Blood coagulation : When blood clotting
occurs, the sol is converted finally into the gel.
4. Fat digestion and absorption : The
formation of emulsions, facilitated by the
emulsifying agents bile salts, promotes fat
digestion and absorption in the intestinal tract.
5. Formation of urine : The filtration of urine
is based on the principle of dialysis.
74. SURFACE TENSION
• It is the force acting perpendicularly inwards
on the surface layer of a liquid to pull its
surface molecules towards the interior of the
• It makes minimum contact area and keeps the
surface like a stretched membrane.
• Due to the phenomenon of surface tension,
any liquid occupies the minimum possible
75. • lt is expressed as dynes/cm.
• Surface tension decreases with increase in
• Solutes: Solutes in liquid raise ST which are
dispersed in liquid.
• While solutes concentrating on the liquid
surface lower the ST.
1. Digestion and absorption of fat :
Bile salts reduce the surface tension. They act as
Detergents and cause emulsification of fat for
effective digestion and absorption.
2. Hay's sulfur test :
This is a laboratory test employed for the
detection of bile salts in urine of jaundice
3. Surfactants and lung function :
• The low surface tension of the alveoli keeps them
apart and allows an efficient exchange of gases in
• Certain surfactants, predominantly dipalmitoyl
phosphatidyl choline (dipalmitoyl lecithin) are
responsible for maintaining low surface tension in
• Surfactant deficiency causes RESPIRATORY
DISTRESS SYNDROME in the infants.
78. 4. Surface tension and adsorption :
Due to the coupled action of these two
processes, the formation of complexes of
proteins and lipids occurs in the biological
5. Lipoprotein complex membranes :
The structure of plasma membrane is composed
of surface tension reducing substances, namely
lipids and proteins.
This facilitates absorption ofthese compounds.
• Viscosity is the internal resistance against the free
flow of a liquid to the frictional forces between the
fluid layers moving over each other at different
• The coefficient of viscosity (η)
• It is the force (dynes) required to maintain the
streamline flow of one fluid layer of 1 cm2 area over
another layer of equal area, separated from one
another by 1 cm, at a rate of 1 cm/sec.
80. • Factors Affecting Viscosity
• Viscosity is directly proportional to density.
• If a small sphere of radius r, and density p falls vertically
through a liquid of density p’ at a steady velocity u in
spite of the acceleration ‘g’ due to gravity, then the
coefficient of viscosity of the liquid is given by η=
• The above is called Stoke’s law.
81. • Temperature:
• Viscosity of the solution decreases with the rise
• This is due to increase in kinetic energy of
molecules for overcoming the resistance due to
intermolecular attractions and also for breaking
intermolecular H bonds of associated liquid.
82. • Size and shape of solute particles:
• Viscosity varies directly with the size and
asymmetry of the solutes or suspended particles.
• A large or elongated molecule imparts higher
viscosity, e.g. fibrinogen.
• Colloidal state: Lyophilic colloids have higher
viscosities than pure liquid.
83. • Unit of Viscosity
• The unit of viscosity is ‘Poise’, named after
Poiseuille,the French man who first devised methods
for measuring viscosity.
• It is force in dynes, necessary to be applied to an area
of 1 sq cm between two parallel planes 1 sq cm in area,
and 1 cm apart, to produce a difference in streaming
velocity between the liquid planes of 1cm/sec.
• Absolute viscosity of water at 25°C is 0.00395 Poise
and is generally used in plotting the viscosity of liquid
84. BIOMEDICAL IMPORTANCE
• Viscosity of whole blood :-
• It depends on protein content of plasma but more on the
number of RBCs.
• Blood cells behave like suspended particles and increase the
viscosity of blood.
• Higher the number of blood cells, greater is the viscosity.
• Thus in polycythemia, viscosity is high while in chronic
anemia it is low.
85. • Resistance against blood flow:
• Resistance against blood flow is directly
proportional to the blood viscosity and the vessel
length but inversely proportional to the fourth
power of the vessel radius.
• Turbulence in blood flow: Blood viscosity helps in
stream lining blood flow by reducing turbulence.
86. • Hemodynamics:
• By influencing resistance and turbulence,
blood viscosity helps in hemodynamics.
• Increase in viscosity may reduce circulation in
chilled extremities, contributing to frostbite
87. • Vitreous body :
• This is an amorphous viscous body located in
the posterior chamber of the eye. It is rich in
albumin and hyaluronic acid.
• Synovial fluid :
• It contains hyaluronic acid which imparts
viscosity and helps in the lubricating function
It refers to a process in which small molecular compounds
will pass through semi-permeable membrane where as
colloids are retained
In this technique , protein sample is placed in a container
composed of semipermeable membrane (such as cellophane)
of different pore size
The container is placed in a buffer solution
When immersed in a solution, smaller molecules diffuse
through membrane while large molecules are retained within
1. Haemodialysis: Removal of salts, creatinine from blood in
case of renal failure.
2. Microdialysis: Removal of extracellular fluid, hormones for
analysis and to determine their concentrations in the body
3. Electrodialysis: It is used to transport salt ions from one
solution through ion-exchange membranes to another
solution under the influence of an applied electric potential
92. GIBBS-DONNAN MEMBRANE
• When two solutions containing diffusible and non-
diffusible ions are separated by a semipermeable
membrane, the non-diffusible ions enhance the
diffusion of oppositely charged diffusible ions.
• The diffusion takes place towards non-diffusible ion
93. • As a result, on the side which contains non-
diffusible ions, diffusible counter ions are more
concentrated while the like charged diffusible
ions concentrate more on the opposite side.
• This is called as Gibbs-Donnan effect.