PLATELETS

• MEGAKARYOPOIESIS: megakaryocyte production
• THROMBOPOIESIS: platelet production
• THROMBOPOIESIS: shedding of the cytoplasm of megakaryocyte to become platelets/ thrombocytes
• MEGAKARYOBLAST (MK-I): Resemble myeloblast and pronormoblast

  • Cannot distinguish from one another (all do not have granules)
• PROMEGAKARYOCYTE (MK-II): Cytoplasm is abundant, with minimal lobularity
• PROMEGAKARYOCYTE (MK-II): Distinguishable with other cell, in terms of size
• MEGAKARYOCYTE (MK-III):

  • Nucleus is lobulated and basophilic (with granules)
  • Cytoplasm is granular and azurophilic (more bluish)
  • With demarcation system (DMS)
• Demarcation system (DMS): Marks the boundary of the true cytoplasm from an extension cytoplasm
• Requirement/condition for it to become a platelet: Megakaryocytes should have at least 4 nuclei to shed off platelets
• METAMEGAKARYOCYTE: There is already a complete DMS where future platelets are derived from
• Platelets are originated from megakaryocyte cytoplasm
• Platelet shedding (Layman's term) = thrombopoiesis
• Macrophage → divides cytoplasm into small pieces = PLATELETS
• Platelet

  Size: 2 – 4 um (2.5 um)
• Platelet

  Mean Platelet Volume (actual): 7 fL (8 – 10 fL)

  MPV (automation): 2-20 fL
• Platelet

  Lifespan: 9 – 10 days (8 – 11 days)
• Platelet

  Normal count: 150 – 450x109/L (150 – 400x109/L)
• Women have higher platelet count (inborn)
• Platelet count

  o   Men: 120 – 350

  o   Women: 140 – 379
• Distribution:

  o   Normal sequestration in spleen: 1/3
• Distribution:

  o   In circulation: 2/3
• Not all are in circulation, otherwise = prothrombic
• Thrombopoietin (TPO): Induces proliferation and production
• Thrombopoietin (TPO): Has two targets: megakaryocyte (TPO stimulates BM to produce megakaryocyte) and platelet
• IL-3, IL-6, IL-11: Are growth factors or cytokines that acts with TPO in order to do thrombopoiesis
• IL-3, IL-6, IL-11: Induces platelet shedding
• RESTING PLATELET: or CIRCULATING PLATELET
• RESTING PLATELET: Normally biconvex

  For peripheral circulation
• RESTING PLATELET

  • EDTA: rounder (1D)
  • Wright–stained smear: circular (2D) or irregular
  • MPV: 7 fL
  • Size: 2-4um
• RESTING PLATELET: Flow smoothly in veins
• It moves back and forth from venules to the white pulp (sequestration)
• Sequestered platelet: Platelet circulating in the spleen
• STRESS PLATELET: or RETICULATED PLATELET
• STRESS PLATELET: Markedly larger than normal platelet and irregular
• STRESS PLATELET: Appears particularly in thrombocytopenia
• STRESS PLATELET: High level of stress platelets = prone to cardiovascular disease
• STRESS PLATELET

  • EDTA: rounder
  • Citrated blood: cylindrical or beaded appearance
  • MPV: 12-14 fL
  • Size: >6um
• STRESS PLATELET: Carry ribosomes and fragments of rough endoplasmic reticulum (just like RBC)
• STRESS PLATELET: Comes from rapid proplatelet extension and release
• STRESS PLATELET: Prothrombic – aggressive in making clots