Disorders of the excretory system

When the kidneys malfunction, urea builds up in the blood: uremia. It is highly harmful and may lead to kidney failure.

In such patients urea can be removed by haemodialysis. Blood is drained from a convenient artery, an anticoagulant such as heparin is added, and it is pumped into a dialysing unit, the artificial kidney.

The unit holds a coiled cellophane tube bathed in dialysing fluid that has the same composition as plasma except for the nitrogenous wastes.

The porous cellophane lets molecules pass according to their concentration gradient. Because the dialysing fluid has no nitrogenous wastes, these move out freely and the blood is cleared.

The cleared blood has anti-heparin added and is pumped back into the body through a vein.

Kidney transplantation is the ultimate way to correct acute renal (kidney) failure. A working kidney from a donor, preferably a close relative, is used to reduce the chance of rejection by the host's immune system.

Renal calculi are stones: insoluble masses of crystallised salts (oxalates and others) formed inside the kidney.

Glomerulonephritis is inflammation of the glomeruli of the kidney.