Platelet cytology

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

Ultra-structurally, 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

Reference

1. Montague SJ, Lim YJ, Lee WM, Gardiner EE. Imaging Platelet Processes and Function-Current and Emerging Approaches for Imaging in vitro and in vivo. Front Immunol. 2020;11:78