This document summarizes passive diffusion and related transport mechanisms. It was submitted by a medical student for their first year studying at MBBS. It describes two main types of passive transport: simple/passive diffusion and facilitated diffusion. Simple diffusion occurs through the lipid or protein layers of the cell membrane for lipid-soluble or water-soluble substances, respectively. Facilitated diffusion uses carrier proteins to transport larger molecules like glucose and amino acids that cannot pass through channels. Various factors can influence the rate of diffusion across membranes.

1. Guided by:
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
Submitted by:
Adnanahmadkhan
Rollno. : 07(Mbbs ist year)
PASSIVE DIFFUSION

2. INTRODUCTION
 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
movement.

3. TYPES OF DIFFUSION
 There are 2 types of Diffusion;
 Simple Diffusion/ Passive diffusion
 Facilitated diffusion

4. CLASSIFICATION
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
and alcohol.
Protein layer: It is permeable to water soluble
substances ,mainly electrolytes diffuse through
this layer.

5. SIMPLE DIFFUSION

6. 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
molecules.
Charcteristic feature : selective permeability

7. 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)

8. 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 /
ligands.
 Mechanically gated channels :
>Opened by some mechanical factors.

9. FACILITATED DIFFUSION
 Water soluble substances having larger molecules are
transported through the cell membrane with the help of
carrier proteins.
 GLUCOSE and AMINO ACIDS are transported by
facilitated diffusion.
 Diameter of these molecules > Diameter of the
channels
So these molecules cannot diffuse through them.

10. FACILITATED DIFFUSION

11. FACTORS AFFECTING RATE OF DIFFUSION
1. Permeability of cell membrane
2. Temperature
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

13. PASSIVE TRANSPORT : SPECIAL
TYPES
 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
the lungs.
 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

14. OSMOSIS
 Movement of water or any other solvent from
area of low concentration to area of high
concentration of solute through semi-
permeable membrane.
TYPES
1.ENDOSMOSIS
2.EXOSOMOSIS

15. OSMOSIS

16. REFERENCES :
$ Guyton and Hall
$ Sembulingam

17. THANK YOU