Short overview of the topic: Kidneys

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  • Created by: jenny100
  • Created on: 16-05-12 13:33


  • Kidneys get rid of toxic waste like urea as well as adjusting the amount of dissolved iond and water in the blood

Nephrons are the filtration units in the kidneys

  • Ultrafiltration: High pressure is built up which squeezes water, urea, ions and sugar out of the blood and into the Bowman's capsule. Membranes between the blood vessels and the Bowman's capsule act as filters, not allowing big molecules to pass through (protein and blood cells)
  • Reabsorbtion: As the liquid flows along the nephron useful substances are reabsorbed into the blood: all  the sugar is reabsorbed via active transport, sufficient ions and water are also reabsorbed
  • Release of wastes: the remaining substances (including urea) continue out of the nephron, into the ureter and down the bladder as urine
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Kidney Failure

  • If the kidneys don't work properly waste substances buil up in the blood and you lose your ability to control the levels of ions and water in your body
  • There's two treatments available if the kidneys stop working - regular dialysis or a transplant

Dialysis machines filter the blood

  • Dialysis must be done regularly to keep the concentration of dissolved substances in the blood at normal levels and remove waste substances
  • In a dialysis machine the blood flows along a selectively permeable barrier surrounded by dialysis fluid. It's permeable to things like ions and waste substances but not big molecules like proteins (acts just like membranes in the kidneys)
  • The dialysis fluid has the same concentration  of dissolved ions and glucose as healty blood
  • This means useful dissolved ions and glucose won't be lost from the blood during dialysis
  • Only waste substances (urea) and excess ions and water diffuse across the barrier
  • Many patients have to have dialysis sessions three times a week taking 3-4 hours for each session.

Dialysis machines are expensive for the NHS to run and its not a pleasant experience

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Kidney Failure 2

Transplanted Organs can be rejected by the body (patients immune system), it's treated as a foreign body and attacked by antibodies:

  • A donor with a tissue type that closely matches the patient is chosen - based on the type of antigens that are on the surface of the cells
  • Patients bone marrow is blasted with radiation to stop white blood cells being produced so they won't attack the transplanted kidney. Drugs also have to be taken to suppress the immune system
  • This means the patient can't fight diseases (without the white blood cells) so they have to be kept in sterile conditions some time after the operation 
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