Passive membrane transport

Passive Membrane Transport

Passive membrane transport is the movement of chemical substances across cell membranes. Passive membrane transport can also be described as the net overall movement of chemical substances from an area of high concentration to an area of low concentration across a membrane. However, due to this transport being "passive" there is no need for chemical energy to be input at the start of the process.

"Uses of Passive Membrane Transport in the body and clinical Medicine"

Passive membrane transport is important in the body because there are many homeostatic functions which require passive transport in order to occur. For example water reabsorption which occurs in the kidneys specifically loop of Henle. The loop of Henle creates a very negative water potential around the medulla of the kidney by transporting salts from the ascending limb to the descending limb. Due to this difference in water potential the water molecules can be reabsorbed by osmosis. One type of therapy for Kidney failure is dependent on this process is Dialysis. This occurs when waste,excess fluids and salts are run through a dialysis membrane which contains dialysis fluid, due to the difference in concentration of certain substances the waste, excess fluids and salts are removed from the patients blood by diffusion, ensuring the composition of the patients blood plasma is correct before re-entering their body. The correct composition of the blood plasma upon re-entering is ensured because the dialysis fluid has the same concentration of substances as normal blood plasma does.

"Different Types of Passive membrane transport "

There are four different types of Passive membrane transport, these are: Diffusion, Osmosis, Facilitated diffusion and Filtration. Diffusion is the net overall movement of particles from an area of high concentration to an are of low concentration. Osmosis is the movement of water molecules from an area of high concentration to an are of low concentration, however, unlike diffusion Osmosis can only occur across a semi-permeable membrane. Facilitated diffusion follows the same movement as the diffusion however, this process requires specialised proteins to "carry" these particles through the semi-permeable membrane. Finally, Filtration doesn't depend on the difference in concentration of substances it depends on the pressure gradient, the particles will move from an area of high pressure to an area of low pressure.

Sources: http://en.wikipedia.org/wiki/Passive_transport Luiz Carlos Junqueira, José Carneiro. Basic Histology. 11th Edition. 2005 ISBN 9780071118880