2. CONTENTS
INTRODUCTION
FICK’S LAW OF PASSIVE DIFFUSION
CHARACTERISTICS OF PASSIVE DIFFUSION
WHYTHIS DIFFUSION IS CALLED AS PASSIVE
DIFFUSION?
A DIAGRAM SHOWS PASSIVE DIFFUSION
ACROSS PLASMA MEMBRANE
REFERENCE
3. INTRODUCTION
*Passive diffusion
is a movement of
ions or atomic
substances across
cell membrane with
a concentration
gradient without the
need of energy.
*molecules diffuses
from a region of
higher
concentration to
lower concentration
until equilibrium is
attained.
4. FICK’S LAW OF PASSIVE DIFFUSION
Fick’s law states that the molecule or drug diffuses from
higher concentration to lower concentration with a
concentration gradient until equilibrium is attained.
Mathematically,
dQ/dt = DAKm/w (CGIT-C)
h
where,dQ/dt=Rate of diffusion
D=Diffusion coefficient
A=Surface area of membrane
Km/w=Partition coefficient
(CGIT- C)= Concentration gradient
h=Thickness of the membrane
5. CHARACTERISTICS OF PASSIVE
DIFFUSION
The drug molecules moves down the
concentration gradient indicating downhill
transport.
This process is energy independent.
This process is rapid over short distance and
slower over long distance.
The rate of drug transfer is directly proportional
to the concentration gradient between GI fluid
and blood compartment.
Absorption of more than 90% of drug is done by
passive diffusion.
6. CHARACTERISTICS
The process is non – saturable.
Greater the membrane or water partition
coefficient of drug, faster the absorption.
The passive diffusion follows first order
kinetics.
Greater the area and lesser the thickness of
the membrane, faster the diffusion; thus,
more rapid is the rate of drug absorption
from the intestine than from the stomatch.
7. WHY THIS DIFFUSION IS CALLED
AS PASSIVE DIFFUSION ?
This diffusion is called as passive diffusion
because this process is energy independent
or does not require any energy to move from
higher concentration to the lower
concentration because the movement of drug
is a result of the kinetic energy of molecules.
