Disorders of the Excretory System

When the kidneys fail to work properly, waste that they would normally clear begins to build up in the body, and this can become dangerous. Several distinct disorders and the ways of managing them are described here.

Uremia

If the kidneys malfunction, urea accumulates in the blood, a condition known as uremia. This is highly harmful and, if unchecked, can progress to kidney failure. The excess urea can be removed artificially by a process called haemodialysis.

Haemodialysis

Haemodialysis is essentially a way of cleaning the blood outside the body using an artificial kidney.

• Blood is drawn from a convenient artery and, after an anticoagulant such as heparin is added to stop it clotting, it is pumped into a dialysing unit (the artificial kidney).
• Inside this unit is a coiled tube made of porous cellophane, surrounded by a special dialysing fluid. This fluid has the same composition as blood plasma except that it contains no nitrogenous wastes.
• Because the cellophane membrane is porous, molecules can pass across it according to their concentration gradient. Since the dialysing fluid holds no nitrogenous wastes, these wastes move freely out of the blood and into the fluid, thereby cleaning the blood.
• The cleared blood is then returned to the body through a vein, but only after anti-heparin is added to it.

This technique has proved to be a great relief for thousands of uremic patients across the world.

Kidney transplantation …