The kidneys- B3 AQA

All the points from the AQA specification about "how do exchanges in the kidney help us to maintain the internal environment in mammals and how has biology helped us to treat kidney disease?"

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  • Created by: LaurenE
  • Created on: 18-05-12 19:05


People whose kidneys do not funciton properly die because toxic substances accumulate in their blood. Their lives can be saved by using dialysis machines or having a healthy kidney transplanted.

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A healthy kidney

A healthy kidney produces urine by:

  • First filtering the blood so that only substances which are too big to be filtered out (such as protein and blood cells) remain. This is known as ultrafiltration and it occurs because a high pressure is built up which squeezes substances out of the blood and into the Bowman's capsule.
  • Then it reabsorbes all the sugar. This involves the process of active transport against the concentration gradient.
  • Sufficient ions are reabsorbed (as much ions as the body needs). Excess ions are not. Active transport is used for this.
  • Sufficient water is reabsorbed (as much as is necessary).
  • Finally it releases urea, excess ions and water as urine.

Sugar and dissolved ions may be actively absorbed against a concentration gradient.

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Dialysis is one of the methods used to treat kidney failure.Whilst it doesn't cure you, it does stop you from dying.

In a dialysis machine, a person's blood flows between partially permeable membranes. The dialysis fluid contains the same concentration of useful substances as the blood. This ensures that glucose and other useful mineral ions are not lost. Urea passes out from the blood into the dialysis fluid. Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels and has to be carried out at regular intervals.

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Kidney Transplants

A kidney transplant enables a diseased kidney to be replaced with a healthy one from a donor. However, the donor kidney  may be rejected by the immune system unless precautions are taken.

To prevent rejection of the transplanted kidney:

  • A donor kidney with a "tissue-type" similar to that of the recipient is used.
  • The recipient is treated with drugs that suppress the immune system.
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Advantages and disadvantages of dialysis


  • Some people cannot have a transplant so dialysis is the only option for them.
  • Relatively available.


  • Has to happen regularly- 3 times a week or everyday depending on the type of dialysis
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Advantages and disadvantages of a transplant


  • It can be cheaper over time.
  • Freedom from dialysis.
  • Can lead a normal life.


  • The kidney might be rejected.
  • Have to take drugs for the rest of your life to prevent rejection.
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