Treating Kidney Failure (WJEC GCSE Biology)

• The kidneys might not work properly for several reasons, including injury or disease
• Humans can survive with one functioning kidney, but if both are damaged then there will quickly be a build-up of toxic urea
  • This build-up can be fatal so treatment is essential
• Dialysis is the usual treatment for someone with kidney failure
• Patients are connected to a dialysis machine which removes most of the urea and restores the water and salt balance of the blood

Kidney failure options diagram

People who suffer from kidney failure may be treated by organ transplant or dialysis

Higher Tier Only

• Unfiltered blood is taken from an artery in the arm, pumped into a dialysis machine and then returned to a vein in the arm
• Inside the machine, the blood and dialysis fluid are separated by a partially permeable membrane
• Dialysis fluid contains:
  • A concentration of glucose and salts that is similar to normal blood levels
    • Any excess glucose and salts will diffuse out of the blood into the fluid until equilibrium is reached
    • Levels of blood glucose and salts will not decrease below normal levels
  • No urea
    • Urea will diffuse out of the blood and into the fluid down its concentration gradient
• The blood flows through the machine in the opposite direction to dialysis fluid; this is called a counter-current system
  
  • The counter-current system ensures that a concentration gradient is maintained between the blood and the dialysis fluid at all times
  • If the blood and fluid flowed in the same direction then equilibrium would be reached halfway along and diffusion would stop

Dialysis diagram

Dialysis is an artificial method of filtering the blood to remove toxins and excess substances