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MLAB 1227: Coagulation Keri Brophy-Martinez

MLAB 1227: Coagulation Keri Brophy-Martinez. The Platelets. All About Platelets…. Second major component of the hemostatic system. Platelets. What is a platelet? Small 2-3 µm Disc-shaped Anuclear Reddish-purple granules Fragments of megakaryocyte cytoplasm

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MLAB 1227: Coagulation Keri Brophy-Martinez

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  1. MLAB 1227: CoagulationKeri Brophy-Martinez The Platelets

  2. All About Platelets… • Second major component of the hemostatic system

  3. Platelets • What is a platelet? • Small 2-3 µm • Disc-shaped • Anuclear • Reddish-purple granules • Fragments of megakaryocyte cytoplasm • Surface has a sponge-like look, openings are channels that extend deep within cell

  4. Platelets • Life span • 9-10 days • Reference Range • 150-450 x 109 /L

  5. Platelet: Side noteSeen in conditions with increased need and/or destruction • Giant platelets • Micromegakaryocytes= Dwarf Megs • May Hegglin anomaly, Bernard-Soulier syndrome, pregnancy,

  6. Anatomy of a Platelet • Divided into 4 zones • Peripheral • Structural • Organelle • Membrane

  7. Peripheral zone: • Responsible for platelet adhesion and aggregation • Glycocalyx: Fluffy surface coat • Contains glycoprotein receptors: • GPIb binds von Willebrand’s factor needed for platelet adhesion to collagen • GPIIb/IIIa binds fibrinogen needed for aggregation • Bind ADP and thrombin, promoting aggregation • Factors I, V, VIII on surface, involved in 2o hemostasis • Membrane: • Exposed on platelet activation • Layer called PF3 (platelet factor) surface for interaction of plasma coagulation factors • Initiation of formation of thromboxane A2. This stimulates aggregation and vasoconstriction

  8. Structural/ so-gel zone • Responsible for platelet retraction/contraction functions and platelet shape • Microtubules/Microfilaments • Cytoskeleton • Binding proteins • Actin • Myosin

  9. Organelle zone • Responsible for storage and platelet release functions • Granules • Dense bodies, alpha granules, lysosomal granules and microperoxisomes • Mitochondria • Glycogen

  10. Membrane Zone • Responsible for secretion of granule contents and storage of calcium • Two systems • Surface-connected open canalicular system (OCS) • Dense tubular system(DTS)

  11. Anatomy of a Platelet • http://www.platelet-research.org/1/function_morpho.htm#

  12. Production of Platelets • Made in Bone marrow • Need dictates the amount of platelets produced. • Stimulus for production is the platelet mass in circulating blood ~ 80 % and megakaryocyte mass in bone marrow • Originate from CFU-GEMM to form CFU-Meg • Cytokines and growth factors such as IL-3 and GM-CSF influences progenitor stages

  13. Platelet Development • Megakaryoblast • 10-15 µm • Increased nuclear: cytoplasmic ratio • Promegakaryocyte • 80 µm • Dense alpha and lysosomal granules • Basophilic megakaryocyte • Megakaryocyte

  14. Production of Platelets • Precursor Cell= Megakaryocyte • Produces about 2000 platelets • Platelets are released via sinuses of bone marrow • 2/3 pb • 1/3 sequestered in spleen

  15. Production of Platelets • Thrombopoietin (TPO) • Regulates platelet development • Influences all stages of megakaryocyte production • Produced in the liver, kidney and spleen

  16. Production of Platelets • How does TPO work? • Maintains a constant number of platelets in peripheral blood by binding Mpl (platelet receptor). Bound TPO can not stimulate proliferation of bone marrow progenitor cells • The higher the platelet count, the more TPO is bound and stimulation of bone marrow is decreased.

  17. References • McKenzie, Shirlyn B., and J. Lynne. Williams. "Chapter 29." Clinical Laboratory Hematology. Boston: Pearson, 2010. Print. • Platelet Research Laboratories. Platelet Function. Retrieved from http://www.platelet-research.org/1/function_hemo.htm.

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