Biology 3 - 13.4 The Kidneys

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A healthy kidney produces urine by:

  • first filtering the blood 
  • reabsorbing all the sugar 
  • reabsorbing the dissolved ions needed by the body
  • reabsorbing as much water as the body needs
  • releasing urine, excess ions and water as urine

Urea is produced in the liver and then excreted by the kidney to the bladder.


Ultrafiltration happens in the Bowman's capsule in the kidneys. All small molecules filtered into the proximal's tubule are glucose, ions, water and urea. Large molecules are not filtered out of the glomerulus e.g. proteins and blood cells.


This happens in the kidney tubule. The blood reabsorbs sugar, necessary ions and the amount of water that the body needs. Everything else is excreted to the bladder to form urine. Urine contains water, urea and the excess mineral ions…



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