Megakaryocytopoiesis Overview
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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?

  • Megakaryoblasts
  • Granular megakaryocytes
  • Mature megakaryocytes
  • Promegakaryocytes (correct)
  • 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?

  • Glycogen granules
  • Open canalicular system
  • Microtubule system
  • Mitochondria (correct)
  • Which of the following granulocytes are not present in mature platelets?

    <p>Beta granules</p> Signup and view all the answers

    How large can mature megakaryocytes grow during maturation?

    <p>Up to 100 µm</p> Signup and view all the answers

    Which glycoprotein is NOT mentioned as part of the glycoproteins rich in the glycocalyx of platelets?

    <p>Glycoprotein IIa</p> Signup and view all the answers

    What system within platelets is responsible for direct communication between intracellular and extracellular compartments?

    <p>Open canalicular system</p> Signup and view all the answers

    What is the main function of microtubules and contractile microfilaments in platelets?

    <p>Active contraction for secretion</p> Signup and view all the answers

    What is one function of alpha granules in platelets?

    <p>Binding of platelets to collagen</p> Signup and view all the answers

    What component is found within the organelle zone of platelets?

    <p>Glycogen particles</p> Signup and view all the answers

    Which substance is NOT contained in dense (delta) granules?

    <p>Platelet-derived growth factor (PDGF)</p> Signup and view all the answers

    Which component is primarily associated with the maintenance of platelet shape?

    <p>Microtubules</p> Signup and view all the answers

    What is the lifespan of a platelet?

    <p>8-12 days</p> Signup and view all the answers

    Which function is attributed to β-Thromboglobulin in platelets?

    <p>Chemoattraction</p> Signup and view all the answers

    What is located in the peripheral zone of platelets?

    <p>Cytoplasmic membrane</p> Signup and view all the answers

    Which granule type in platelets mainly contributes to secondary hemostasis?

    <p>Delta (dense) granules</p> Signup and view all the answers

    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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    Related Documents

    HEMA 1 Lecture 4 Platelets PDF

    Description

    This quiz explores the process of megakaryocytopoiesis, detailing the stages of maturation including megakaryoblasts, promegakaryocytes, and mature megakaryocytes. Understand the significance of endomitosis in the development of thrombocytes. Test your knowledge of hematopoiesis today!

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