MLAB1315- Hematology
Fall 2007
Keri Brophy-Martinez
Unit 4: Platelets
Platelets: maturation sequence
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Production occurs in the bone marrow
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Megakaryoblast
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Size: 20-45µm
Cytoplasm
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–
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Nucleus
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–
–
–
–
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Blue, scanty, pseudopodia
No granules
Single, round/oval, may be indented
Central or eccentric
Red purple with fine and distinct chromatin
1-2 nucleoli
Nucleus divides by endoreplication meaning the nuclear material
reduplicates, but the nucleus does not divide resulting in a multilobed
nucleus and abundant cytoplasm.
N:C ratio = 4:1
Megakaryoblast
Promegakaryocyte
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Size: 20-80µm
Megakaryocyte
–
–
Size: 30-100µm
Cytoplasm
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
–
Nucleus
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–
–
Pinkish blue/abundant
Irregular border with occasional pseudopods
Abundant granules
Lobulated
Purple with granular chromatin
No nucleoli
N:C ratio = 1:1 to 1:12
Membrane ruptures after maturation is complete, cytoplasm
fragments resulting in 1000 to 2000 platelets. The nucleus
is phagocytized.
Megakaryocyte
Platelet (thrombocyte)
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
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Normal range: 150,000 - 450,000/µl
Size: 1-4µm
Cytoplasm
–
–
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Light blue (actually fragments of megakaryoctye
cytoplasm)
Fine scattered granules
Nucleus not present
Lifespan is 8-10 days
Platelet (thrombocyte)
Function of platelets
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Normally circulate in a discoid shape
Help to maintain hemostasis and capillary integrity (this will be
discussed in detail in Coagulation)
When vascular injury occurs, platelets do the following:
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–
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–
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Adhere to the injured vessel
Aggregate and transform into reactive spiny spheres that interact with one
another and form into a platelet plug
Consolidate with fibrin into a clot
Stabilize with the aid of a coagulation factor
Platelets contain the following storage granules that are released when
the platelets adhere to the vessel surface:
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–
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Alpha
Dense
Delta