MLAB1415- Hematology

Keri Brophy-Martinez

Platelets

Platelets

Production– Bone marrow

Differentiation– Comes from the CFU-GEMM

Platelets

Regulation– TPO= thrombopoietin

Influences all stages of megakaryocyte production Made in liver, kidney and spleen Binds receptors in peripheral blood

– Bound TPO does not stimulate bone marrow progenitor cells

– For example: Increased platelet count, more TPO is bound, stimulation of bone marrow is decreased

Function of platelets

Normally circulate in a discoid shape

Help to maintain hemostasis and capillary integrity (this will be discussed in detail in Coagulation)

Platelet to platelet interactions

Platelet to coagulation protein interactions

Aid in healing injured tissue

Overview of Hemostasis

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: maturation sequence

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

Megakaryoblast

Promegakaryocyte

Size: 20-80µm Cytoplasm:

– Basophilic– Few azurophilic granules

Nucleus– Indented or bilobed

nucleus

Megakaryocyte

– Size: 30-100µm– Cytoplasm

Pinkish blue/abundant Irregular border with occasional pseudopods Abundant granules

– Nucleus Lobulated Purple with granular chromatin No nucleoli

– N:C ratio = 1:1 to 1:2– Membrane ruptures after maturation is complete, cytoplasm

fragments resulting in 1000 to 2000 platelets. The nucleus is phagocytized.

Megakaryocyte

Platelet (thrombocyte)

Size: 1-4µm Cytoplasm

– Light blue (actually fragments of megakaryoctye cytoplasm)– Fine scattered granules

Nucleus not present

Reference range: 150,000 - 450,000/µl Lifespan is 8-10 days

Platelet (thrombocyte)

Platelets

References

Harmening, D. M. (2009). Clinical Hematology and Fundamentals of Hemostasis. Philadelphia: F.A Davis.

McKenzie, S. B., & Williams, J. L. (2010). Clinical Laboratory Hematology . Upper Saddle River: Pearson Education, Inc.