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“Football and Dialysis”

The “Agar Patented Explanation” of:


How Dialysis Works


(With apologies to the Geelong Football Club)




Imagine an Australian Rules Football Oval, though any football arena would do…

Out in the middle… The Geelong Cats are warming up like a well-oiled machine!


        There are two equal sized spectator areas

        The two enclosures are separated by a chain-mesh fence

        Each enclosure has a locked gate awaiting the gatekeeper to arrive

        The gate-keeper of one enclosure opens the gate letting in the Cats fans, adults and kids




        The other gatekeeper sleeps in. His gate stays locked. 

        All the supporters are therefore crowded into the one enclosure!







       GO CATS                              GO CATS                                        
















This causes problems


        The kids can’t see the game over the adults heads

        Kids being kids, some see the holes in the chain-mesh fence … and what would YOU do if you were a small kid?


The result


        They begin to crawl through the holes leaving the adults in the other enclosure.

        Over time, the number in each enclosure would equalize, giving the best view to all



















But not everyone is happy



        The police are furious ... kids can’t do that!

        They arrest the kids and take them away

        Suddenly … one enclosure is empty again
















And the cycle continues


        The remaining kids with the adults can’t resist the holes in the fence and the empty enclosure 

        The Cats are ‘on fire’ and they want a better view! 

        As the police leave with the first ‘offenders’ …

        The remaining kids crawl through the fence to get a better view of the game

        As they do, the number staying with the adults falls even further





















So … what is the principle happening here?


        During the game, the smaller people cross through the fence for a better view but are constantly removed by the police

        By game’s end, both enclosures are emptied of ‘small people’ by:


(i)  a constant escape through the fence - (this demonstrates the "Principle of Diffusion")

(ii) a constant removal by the police



In dialysis…



       Like we have just seen occurring in the example of the football crowd, a crowd in any crowded space will tend to disperse to a less crowded space if any barrier separating the two spaces can be crossed

        So... if blood which contains high levels of waste (as in kidney failure) can be brought close to a fluid containing no waste, and if the blood and fluid compartments can be separated by a leaky membrane with tiny holes in it across which some of the waste can freely pass, wastes would move through the membrane from the blood into the fluid

        Small wastes would ooze through the holes in the membrane and into the waste-free fluid on the other side... just like the kids crawled through the wire-mesh fence in our example

        If the fluid in the fluid compartment is consistently removed and renewed with fresh, waste free fluid, a continual gradient is created down which more small wastes flow

        So... slowly, the blood is cleansed of its high waste levels





This example of the football crowd serves to illustrate how dialysis works.


        Small wastes pass across a ‘permeable’ membrane and are constantly ‘removed’

        Over time, the blood is slowly cleared of waste material

        However, bigger wastes remain a problem as they take much, much longer to ‘pass through’. 


As a result, time on dialysis actually does matter!



        Not all wastes are small in size

        Some wastes are big and find it much harder and also take longer to squeeeeeeze through the holes in the fence

        The bigger sized wastes therefore need either…

        Considerably more time

        A leakier membrane

        or both!



On two counts, therefore …Time on dialysis matters


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Authored by Prof John Agar. Copyright © 2012
 Nocturnal Haemodialysis Program, Barwon Health.
 All rights reserved. Revised: July 1st 2012