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==Introduction==

|linkpage =Transport Across Membranes - Physiology

|linktext =TRANSPORT ACROSS MEMBRANES

|maplink = Urinary System (Content Map) - Anatomy & Physiology

Gases or liquids can be unevenly distributed between two areas.  If one area has a higher concentration than the other then the differance between these two areas is termed the '''concentration gradient'''.  The equality is then corrected by the movement of the molecules down this so called gradient from the region of high concentration to that of low.  This process is '''passive''' as the molecules do not have to be forced to do this and it is reffered to as '''diffusion'''.

If gases or liquids are unevenly distributed between two areas.  One area having a higher concentration than the other then the differance between those two areas is termed the '''concentration gradient'''.  The equality is then corrected by the movement of the molecules down this so called gradient from the region of high concentration to that of low.  This process is '''passive''' as the molecules do not have to be forced to do this and it is reffered to as '''diffusion'''.

==Ficks Law==

==Ficks Law==

'''D''' = The diffusion coefficient  

 

'''A''' = The cross sectional area which the substance is to diffuse across  

  '''D''' = The diffusion coefficient  

 

  '''A''' = The cross sectional area which the substance is to diffuse across  

'''C₁ C₂''' = The concentrations in the two areas   

  '''C₁ C₂''' = The concentrations in the two areas   

 

  '''L''' = distance separating the two areas

'''L''' = distance separating the two areas

Ficks law demonstrates that the rate of diffusion can be maximised by increasing the area over which diffusion can occur, minimising the distance it has to occur over and increasing the gradient it occurs along.  In the body it tends to be the former two which are taken into account when adapting surfaces for diffusion to occur over.

Ficks law demonstrates that the rate of diffusion can be maximised by increasing the area over which diffusion can occur, minimising the distance it has to occur over and increasing the gradient it occurs along.  In the body it tends to be the former two which are taken into account when adapting surfaces for diffusion to occur over.

==Diffusion Through the Lipid Bilayer==

==Diffusion Through the Lipid Bilayer==

* Lipid soluble substances are able to diffuse freely across the lipid bilayer of cells.   

* Lipid soluble substances are able to diffuse freely across the [[Phospholipid Bilayer - Anatomy & Physiology|lipid bilayer of cells.]]  

* This obviously occurs passively down the concentration gradient.

* This occurs passively down the concentration gradient.

 

If more information is need it can be found [http://en.wikipedia.org/wiki/Passive_diffusion here]

[[Category:Transport Across Membranes]]