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Platelet cytology

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Platelets are disc-shaped and approximately 1-2 micrometers in diameter. Usually forming clumps of platelets, they stain pale blue with Romanowsky stains in blood smears.

Ultrastructurally, they have a very active cytoskeleton. Microfilaments participate in clot retraction while microtubules regulate the overall shape. Mitochondria are evident within the cytoplasm. They are bounded by a mucopolysaccharide outer membrane.

There are two types of granule: lysosomal alpha granules and dense granules. They contain substances vital to function e.g. :

  • dense granules:
    • ADP
    • ATP
    • serotonin, 5HT
  • lysosomal granules:
    • von Willebrand factor
    • platelet-derived growth factor
    • platelet activating factor
    • factor V
    • fibrinogen
    • platelet factor 4

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