If the kidney are so impaired by disease or injury that they are unable to excrete nitrogenous wastes and regulate pH, electrolyte, and water concentration of the plasma, the blood must be cleansed by an artificial device.
Such cleansing of the blood is called hemodialysis.
Dialysis means the separation of large particles from smaller ones through use of a selectively permeable membrane. one of the best known devices for accomplishing dialysis is the artificial kidney machine.
A tube connects it with the patient's radial artery. the patient's blood flow through tubing made oof selectively permeable membrane (dialysis membrane) outside the body.
As blood flows through the tubing, waste products passing from the blood into the dialysis solution or dialysate surrounding dialysis membrane.
Also if nutrients are provided in the solution, they can move from the dialysate into the blood. The dialysate is continuously replaced to maintain favorable concentration gradients between the solution and the blood.
After passing through the dialysis tubing, the blood flows back to the body.
about 500 ml of blood are in the machine at a time. the temporary loss of this volume from the body is easily compensated for by vasoconstriction and increased cardiac output.
In removing wastes from the blood, the dialysis membrane performs one of the kidney's functions.
Hemodialysis typically is performed three times a week, each session lasting for several hours.
There are serious drawback to hemodialysis. Blood cells can be damaged and anticoagulants must be added, which can lead to bleeding problems.
The slow rate at which the blood can be processed makes the treatment time-consuming
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