Kidney diseases are ranked the forth most major disease in the United States. Kidney functions can be impaired by infections, poisoning caused by substances such as mercury, or carbon tetrachloride, by lesions, tumors, kidney stone formation, shock, or by many circulatory diseases. One of the most common disease is glomerulonephritis, which is actually a large number of related chronic diseases in which the glomeruli are damaged. The damage is thought to result from an autoimmune response.

In chronic kidney diseases there is a progressive loss of renal function that may eventually reach the stage of kidney failure. In kidney failure there is a decrease in the glomerular filtration rate and the kidneys are unable to maintain homeostasis of the blood. Homeostatic balance of water, sodium, potassium, calcium, and other salts are no longer possible, and nitrogenous wastes are not excreted. Retention of water causes edema and, as the concentration of hydrogen ions increases, acidosis develops. Nitrogenous wastes accumulate and a condition referred to as uremia develops in the blood and tissues. If untreated, the acidosis and uremia can cause coma and eventually death. Chronic Kidney failure can be treated by Kidney dialysis and Kidney transplant.

Dialysis is a process of separating solutes in a solution by diffusion across a semipermeable membrane. A kidney dialysis machine can be used to restore appropriate solute balance to a patient whose kidneys are not functioning. In extracorporeal dialysis, a plastic tube is surgically inserted in both an artery and a vein in the patients arm or legs. These tubes can then be connected to a circuit of plastic tubing from a dialysis machine. The patients blood flow though the tubing, which is immersed in a solution containing most of the normal blood plasma constituents in their homostatic proportion. The walls of the plastic tubing constitute a semipermeable membrane. Since the dialysis fluid contain no wastes, nitrogenous wastes such as urea pass from the patients blood though minute pores in the tubing and into the surrounding solution. As the blood circulate repeatedly though the tubing in the machine, dialysis continues, eventually adjusting most of the values of the patients blood chemistry to normal ranges. Although much improved by recent engineering advances, machine dialysis is very expensive, clumsy, and inconvenient, and may produce serious side effects such as osteoporosis.

A different dialysis technique, continuous ambulatory peritoneal dialysis (CAPD), makes use of the fact that the peritoneum (the lining of the abdominal cavity) is a differentially permeable membrane. A plastic bag containing dialysis fluid is attached to the patient's abdominal cavity. After about 30 minutes, the fluid is withdrawn into the bag and discarded. This process is repeated about three times a day. This type of dialysis is much more convenient but poses the threat of peritonitis, should bacteria enter the body cavity with the dialysis fluid.

Long term use of dialysis is not as desirable for the patient as would be a funtioning kidney. With a successful kidney transplant, a patient can live a more normal live with far less long term expense. At present more than two thirds of kidney transplants are successful for several years, although physicians must routinely treat the problems of graft rejection. There are several recipients of kidney transplants who have survived for more than 20 years.

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