The Kidney

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  • Created by: Katherine
  • Created on: 01-04-13 09:16

Main Roles

  • Removal of urea from the blood
  • Adjustment of ions in the blood
  • Adjustment of water content in the blood
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A Healthy Kidney Produces Urine By:

  • First filtering the blood through ultrafiltration
  • Then reabsorbing all the sugar, dissolved ions and as much water as the body needs.
  • It then releases urea, excess water and ions as urine
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A Healthy Kidney Produces Urine By:


  • This is when a high pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule.
  • The membran between the blood vessels and the Bowman's capsule act like filters, so big molecules like protein and blood cells can not squeeze out. They stay in the blood.


  • As the liquid flows along the nephron, useful substances are absorbed back into the blood.
  • All the sugar is reabsorbed through the process of active transport, against the concentration gradient.
  • Sufficient ions are reabsorbed by active transport, but excess ions are not.
  • Sufficient water is reabsorbed. 

Release of Waste: The remaining substances (including urea) continue out of the nephron, into the ureter and down to the bladder as urine. 

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Diagram of a Kidney


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Kidney Failure

  • If the kidneys don't work properly, waste substances build up in the blood and you lose the ability to control the levels of ions and water in your body.
  • You get problems in the heat, bones, nervous system, stomach, mouth etc
  • Eventually this results in death
  • People who suffer from kidney failure may be treated either by using a kidney dialysis machine or by having a healthy kidney transplant
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Kidney Dialysis Machines

  • Treatment by dialysis restores the concentrations of dissolved substances in the blood to normal levels, and removes waste substances.
  • It has to carried out at regular intervals. 
  • In a dialysis machine the person's blood flows between particularly permeable membranes, surrounded by dialysis fluid. 
  • The dialysis fluid contains the same concentration of dissolved ions and glucose as healthy blood.
  • This ensures that glucose and useful mineral ions are not lost.
  • Only waste substances, such as urea and excess ions and water diffuse into the dialysis fluid.


  • Many patients have to have a dialysis session three times a week and each session takes 3-4 hours. This can be time consuming and inconfenient.
  • Dialysis may cause blood clots or infections.
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Healthy Kidney Transplant

  • Kidney transplants are the only cure to kidney diseases
  • A disease kidney is replaced with a healthy one from a donor (alive or dead)
  • However, the donor kidney maybe rejected. The recipient's antibodies may attack the antigens on the donor organ as they do not recognise them as part of the recipient's body.
  • Antigens are proteins on the surface of cells.
  • 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 tissue type is based on antigens.
    • The recipient is treated with drug that suppress the immune system so it won't attack the transplanted kidney.
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Dialysis or Transplant

Kidney Dialysis machines are:

  • Expensive to run
  • Not pleasant experience
  • Inconvenient

Transplants are:

  • Cheaper
  • Have long waiting lists
  • Have possibility of rejection
  • Drugs that suppress the immune system can make people vulnerable to other illnesses
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