1. MLAB1315- Hematology Keri Brophy-Martinez
Unit 4: Platelets

2. Platelets: maturation sequence
Production occurs in the bone marrow
Megakaryoblast
Size: 20-45µm
Cytoplasm
Blue, scanty, pseudopodia
No granules
Nucleus
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

3. Megakaryoblast

4. Promegakaryocyte
Size: 20-80µm

5. Megakaryocyte Size: 30-100µm Cytoplasm Nucleus N:C ratio = 1:1 to 1:12
Pinkish blue/abundant
Irregular border with occasional pseudopods
Abundant granules
Nucleus
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.

6. Megakaryocyte

7. Platelet (thrombocyte)
Normal range: 150, ,000/µl
Size: 1-4µm
Cytoplasm
Light blue (actually fragments of megakaryoctye cytoplasm)
Fine scattered granules
Nucleus not present
Lifespan is 8-10 days

8. Platelet (thrombocyte)

9. Function of platelets 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:
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:
Alpha
Dense
Delta