lhh2003
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In dialysis machines, when useful and harmful substances diffuse out of the blood into the dialysis fluid, and then useful substances in huge concentration in the dialysis diffuse back into the blood, what is stopping the tiny harmful substances that also diffused out of the blood also diffusing back into the blood ?

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Stuntman_82
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(Original post by lhh2003)
In dialysis machines, when useful and harmful substances diffuse out of the blood into the dialysis fluid, and then useful substances in huge concentration in the dialysis diffuse back into the blood, what is stopping the tiny harmful substances that also diffused out of the blood also diffusing back into the blood ?

Thanks,
Diffusion is not a specific process so both useful and waste products can enter and exit as the blood flows. But what removes the toxins is the special dialysis fluids that the filtered blood comes in contact with and it does a great job. However, there is still a small proportion that will still get back into the body so it is not a perfect filter, I guess.
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lhh2003
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(Original post by Stuntman_82)
Diffusion is not a specific process so both useful and waste products can enter and exit as the blood flows. But what removes the toxins is the special dialysis fluids that the filtered blood comes in contact with and it does a great job. However, there is still a small proportion that will still get back into the body so it is not a perfect filter, I guess.
This makes sense.

Thank you.
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Jpw1097
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(Original post by lhh2003)
In dialysis machines, when useful and harmful substances diffuse out of the blood into the dialysis fluid, and then useful substances in huge concentration in the dialysis diffuse back into the blood, what is stopping the tiny harmful substances that also diffused out of the blood also diffusing back into the blood ?

Thanks,
Try to understand that diffusion is a dynamic process. Suppose you have lots of toxic substances in the blood (e.g. urea), and very little in the dialysis fluid. Urea molecules will move from the blood into the dialysis fluid, and other urea molecules will move from the dialysis fluid into the blood. However, because there are more urea molecules in the blood, more urea will leave the blood and enter the dialysis fluid than the other way around, it is not a one-way system. And yes, a small amount of urea will remain in the blood.
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