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Questions and Answers
Which stage of megakaryocytic maturation is characterized by the presence of a variable number of nucleoli and coarsening chromatin?
Which stage of megakaryocytic maturation is characterized by the presence of a variable number of nucleoli and coarsening chromatin?
- Megakaryoblasts
- Granular megakaryocytes
- Mature megakaryocytes
- Promegakaryocytes (correct)
What is the primary process involved in the development of megakaryocytes?
What is the primary process involved in the development of megakaryocytes?
- Mitosis
- Endomitosis (correct)
- Apoptosis
- Cytokinesis
Which structure is part of the platelet ultrastucture responsible for energy production?
Which structure is part of the platelet ultrastucture responsible for energy production?
- Glycogen granules
- Open canalicular system
- Microtubule system
- Mitochondria (correct)
Which of the following granulocytes are not present in mature platelets?
Which of the following granulocytes are not present in mature platelets?
How large can mature megakaryocytes grow during maturation?
How large can mature megakaryocytes grow during maturation?
Which glycoprotein is NOT mentioned as part of the glycoproteins rich in the glycocalyx of platelets?
Which glycoprotein is NOT mentioned as part of the glycoproteins rich in the glycocalyx of platelets?
What system within platelets is responsible for direct communication between intracellular and extracellular compartments?
What system within platelets is responsible for direct communication between intracellular and extracellular compartments?
What is the main function of microtubules and contractile microfilaments in platelets?
What is the main function of microtubules and contractile microfilaments in platelets?
What is one function of alpha granules in platelets?
What is one function of alpha granules in platelets?
What component is found within the organelle zone of platelets?
What component is found within the organelle zone of platelets?
Which substance is NOT contained in dense (delta) granules?
Which substance is NOT contained in dense (delta) granules?
Which component is primarily associated with the maintenance of platelet shape?
Which component is primarily associated with the maintenance of platelet shape?
What is the lifespan of a platelet?
What is the lifespan of a platelet?
Which function is attributed to β-Thromboglobulin in platelets?
Which function is attributed to β-Thromboglobulin in platelets?
What is located in the peripheral zone of platelets?
What is located in the peripheral zone of platelets?
Which granule type in platelets mainly contributes to secondary hemostasis?
Which granule type in platelets mainly contributes to secondary hemostasis?
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Study Notes
Megakaryocytopoiesis
- Development through endomitosis results in nuclear division without cell division.
- Stages of megakaryocytic maturation include megakaryoblasts, promegakaryocytes, granular megakaryocytes, and mature megakaryocytes.
Megakaryoblast
- Committed myeloid progenitor cell in early thrombocyte development.
- Nucleus divides without cytoplasmic division, forming giant cells (20-50 µm).
- Round nucleus has 2-6 nucleoli and fine chromatin, with scant basophilic cytoplasm that lacks granules.
Promegakaryocyte
- Size increases to 20-80 µm with an indented or lobulated nucleus.
- Contains a variable number of nucleoli and coarsening chromatin.
- Basophilic cytoplasm begins to show granules; cytoplasmic tags and demarcating membrane system (DMS) start to form.
Megakaryocyte
- Largest cell in the body, with a size up to 100 µm.
- Multilobulated nucleus has coarse chromatin and variable nucleoli.
- Cytoplasm contains numerous small granules that stain purple with Wright's stain.
Thrombocytes (Platelets)
- Size ranges from 2-4 µm; appear as pale blue cells with azurophilic granules.
- Mature platelets are anucleated.
Platelet Ultrastructure
- Glycocalyx: Outer membrane surface rich in glycoproteins serving as receptors (e.g., Glycoprotein Ib, IIb/IIIa, Va).
- Microtubules and Microfilaments: Provide contraction mechanisms to release granule contents.
- Open Canalicular System: Facilitates communication between intracellular and extracellular environments.
- Dense Tubular System: Circles within microtubules, involved in arachidonic acid metabolism and calcium storage.
- Mitochondria: Vital for energy production; glycogen granules offer energy substrate.
- Alpha Granules: Contain contact-promoting factors (e.g., platelet fibrinogen, PDGF, von Willebrand’s factor).
- Dense Granules: Store nonprotein factors (e.g., ADP, ATP, calcium, serotonin).
Platelet Zones
- Peripheral Zone: Comprises the glycocalyx, cytoplasmic membrane, and open canalicular system involving factors like Factor V and von Willebrand’s factor.
- Sol-Gel (Structural) Zone: Contains microtubules and filaments crucial for shape maintenance and activation response.
- Organelle Zone: Holds granules (alpha and delta), lysosomes, peroxisomes, and mitochondria, providing functional substances.
Alpha Granules
- Key components include Factor V & XI for fibrin formation, fibrinogen for platelet aggregation, and vWF for platelet-collagen binding.
- Other constituents include PAI-1 (fibrinolysis inhibitor), PF4 (heparin neutralizing), and thrombospondin (stabilizes platelets).
Delta Granules
- Contains ADP (enhances platelet response), ATP (activates calcium channels), calcium (secondary hemostasis), and serotonin (vasoconstrictor).
Platelet Characteristics
- Reference range for healthy individuals: 150-450 x 10^9/L or approximately 7-21 per high-power field (HPF).
- Average lifespan of platelets is 8-12 days.
- When stained, platelets appear gray-blue with purple granules.
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