DR. M.M. KHAN SIR(H.O.D.)
DR. INDU MA’AM
DR. PUSHPALATA MA’AM
DR. RASHMI MA’AM
DR. SAMREEN MA’AM
DR. MAJID SIR
DR. SANJEEV SIR
Rollno. : 07(Mbbs ist year)
Diffusion is the chemical process by
which passive transport occurs.
Passive transport is the transportof the
substancesalong the concentrationgradient
or electrical gradient or both.
It is also knownas diffusion or downhill
TYPES OF DIFFUSION
There are 2 types of Diffusion;
Simple Diffusion/ Passive diffusion
SIMPLE DIFFUSION/PASSIVE DIFFUSION
Occurs either through lipid layer or protein
layer of the cell membrane.
Lipid layer : It is permeable only to the lipid
soluble substances like oxygen , carbon dioxide
Protein layer: It is permeable to water soluble
substances ,mainly electrolytes diffuse through
PROTEIN OR ION CHANNELS
They have pores that allow passage of ions and small
water soluble molecules.
Called as protein channels as they are lined by protein
Charcteristic feature : selective permeability
REGULATION OF CHANNELS
o Some of the protein channels are continuously open
and most of the channels are always closed.
o Continuously opened channels : Ungated channels
o Closed channels : Gated channels (These channels
are opened only when required)
Gated channel : Types
Voltage gated channels :
>Open whenever there is a change in electrical potential.
Ligand gated channels :
>Open in the presence of some hormonal substances /
Mechanically gated channels :
>Opened by some mechanical factors.
Water soluble substances having larger molecules are
transported through the cell membrane with the help of
GLUCOSE and AMINO ACIDS are transported by
Diameter of these molecules > Diameter of the
So these molecules cannot diffuse through them.
FACTORS AFFECTING RATE OF DIFFUSION
1. Permeability of cell membrane
3. Concentration/Electrical gradient of substances
across the cell membrane
4. Solubility of the substance
5. Thickness of the cell membrane
6. Size of molecules
7. Size of ions
8. Charge of ions
PASSIVE TRANSPORT : SPECIAL
BULK FLOW- Movement of large quantity of substances
from region of high pressure to region of low pressure.
eg:exchange of the gases across the respiratory membrane in
FILTRATION- Movement of water and solutes from an area
of high hydrostatic pressure to an area of low hydrostatic pressure.
eg- occurs in glomerulus of kidneys
Movement of water or any other solvent from
area of low concentration to area of high
concentration of solute through semi-