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Biology A2 homeostasis

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    The principle of dialysis (used effectively as a substitute for the kidneys, which have failed) is to filter out harmful substances (excess water, urea [end-product of protein breakdown (effectively of amino acid breakdown)], excess electrolytes, creattinine, uric acid [end product of DNA and RNA breakdown] out of the blood compartment into the "urine" (in this case, virtual) compartment. This requires the passage of these substances through a membrane that allows them to pass through.(I) Suitable as it is semi-permeable = allows small molecules like urea and Na+, Cl- etc through.Allows excess water to go through by osmosisIt has a good blood supply which means the process of "cleaning" is efficient.(ii) The volume of liquid in haemodialysis is larger = allows quicker filtration(iii) Dialysis fluid could be made to have lower water potential by dissolving extra solutes in it = more water filtered into it by osmosis(iv) Greater distance for substances to travel by diffusionperitoneal membrane may not be semi-permeable any longer = osmosis less efficient
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