Components of Blood - Topic 1 - Edexcel AS

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  • Main component of blood
  • Largely made of water
  • Contains wide range of dissolved substances to be transported around body
  • Contains fibrinogen - soluble substance used in blood clotting
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Erythrocytes - RED blood cells

  • Bioconcave discs
  • Approx. 5 million per mm3 of blood
  • Contain haemoglobin - red pigment which carries oxygen (and hence no nucleus)
  • Formed in red bone marrow of short bones - eg. ribs
  • Limited life of around 120 days
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Leucocytes - WHITE blood cells

  • Much larger than red blood cells
  • Can squeeze through tiny blood vessels as they can change their shape
  • Approx. 4000-11000 per mm3 of blood
  • Contain a nucleaus and colourless cytoplasm
  • Several types
  • Most formed in white bone marrow of long bones - eg. humerus and femur
  • However, lymphocytes are formed in lymph glands and spleen
  • Main function - defend body against infection
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  • Tiny fragments of large cells known as megakaryocytes found in bone marrow
  • About 150 000 - 400 000 platelets per mm3 of blood
  • Involved in clotting of the blood
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