MLS 323: Thrombopoiesis and Platelet Functions
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Questions and Answers

Which of the following substances increases platelet adhesiveness?

  • Epinephrine
  • Thrombin
  • ADP (correct)
  • Serotonin

    • Platelets require a longer time period to adhere to sites of vascular damage compared to erythrocytes.

    False (B)

    What type of proteins are actomycin, myosin, and filamin considered?

    Contractile proteins

    The primary role of platelets in hemostasis includes adhesion and aggregation forming the _____ hemostatic plug.

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

    Which of these components are involved in the recruitment of local platelets during aggregation?

    <p>Fibrinogen bridges (D)</p> Signup and view all the answers

    Match the following agents with their roles in platelet aggregation:

    <p>Collagen = Particulate material that enhances platelet adhesion Thrombin = Proteolytic enzyme that stimulates aggregation Epinephrine = Biological amine that promotes platelet activation Serotonin = Biological amine that aids in hemostasis</p> Signup and view all the answers

    Platelet aggregation is a passive process and does not require energy.

    <p>False (B)</p> Signup and view all the answers

    What is the term for the transformation of platelets from a disc to a sphere, which aids in their function?

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

    What is the primary function of thrombopoietin in the body?

    <p>Regulates platelet production (D)</p> Signup and view all the answers

    Platelets have a normal lifespan of 14-21 days.

    <p>False (B)</p> Signup and view all the answers

    From which type of cell do megakaryocytes arise?

    <p>Hemopoietic stem cell</p> Signup and view all the answers

    Each megakaryocyte can give rise to approximately _____ platelets.

    <p>1000-5000</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Platelet Adhesion = The process by which platelets stick to damaged blood vessels Platelet Aggregation = The clumping together of platelets at the site of injury Megakaryocyte = A large bone marrow cell that produces platelets Thrombopoiesis = The process of platelet formation</p> Signup and view all the answers

    During which process does the megakaryocyte enlarge its cytoplasmic volume?

    <p>Endomitotic synchronous replication (D)</p> Signup and view all the answers

    The normal platelet count ranges from 100,000 to 300,000 cells/uL.

    <p>False (B)</p> Signup and view all the answers

    What is the average size range of a platelet?

    <p>2–4 μm</p> Signup and view all the answers

    What is the primary function of glycoprotein receptors in the glycocalyx?

    <p>Mediating platelet adherence and aggregation (D)</p> Signup and view all the answers

    The granules within mature platelets include only alpha granules and lysosomes.

    <p>False (B)</p> Signup and view all the answers

    What do canaliculi in platelets facilitate?

    <p>Transport of products from granules to the exterior environment.</p> Signup and view all the answers

    The external coat of a platelet that consists of plasma proteins and carbohydrates is known as the ______.

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

    Match the following types of granules with their contents:

    <p>Alpha granules = Heparin and growth factors Dense granules = Serotonin and ADP Lysosomes = Hydrolase enzymes Platelet Cytoskeleton = Microfilaments and microtubules</p> Signup and view all the answers

    Which component directly maintains the discoid shape of the platelet?

    <p>Cytoskeleton (B)</p> Signup and view all the answers

    Dense bodies in platelets contain ADP, ATP, and calcium.

    <p>True (A)</p> Signup and view all the answers

    The primary role of the ______ in platelets is to mediate contact reactions and assist in aggregation.

    <p>glycoprotein receptors</p> Signup and view all the answers

    What is true about the degree of clot retraction?

    <p>It increases with a smaller hematocrit. (C)</p> Signup and view all the answers

    Clot retraction is inversely proportional to the number of platelets.

    <p>False (B)</p> Signup and view all the answers

    What substance is known to induce a long-lasting functional defect in platelets, detectable as a prolongation of the bleeding time?

    <p>Aspirin (D)</p> Signup and view all the answers

    A thrombus is defined as a platelet aggregate reinforced by fibrin.

    <p>True (A)</p> Signup and view all the answers

    Name one agent that can be used to aggregate platelets.

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

    The process of dissolved fibrin clot is known as _____ .

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

    How can the quantitative determination of platelets be assessed?

    <p>Using an electronic particle counter or manual methods involving a stained blood film.</p> Signup and view all the answers

    A prolonged bleeding time, despite a normal platelet count, suggests _____ platelet function.

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

    Which method can be used to analyze platelet adhesion in vitro?

    <p>Measuring adherence to glass surfaces (A)</p> Signup and view all the answers

    Antiplatelet antibodies can be demonstrated in cases of immune thrombocytopenia.

    <p>False (B)</p> Signup and view all the answers

    What is the normal range of platelets visible in a properly prepared blood smear?

    <p>8 to 20 platelets per 100 oil immersion fields (C)</p> Signup and view all the answers

    Bleeding time is an in vivo measurement of platelet adhesion and aggregation on injured vascular subendothelium.

    <p>True (A)</p> Signup and view all the answers

    What type of plasma is treated with aggregating agents to assess platelet function?

    <p>Platelet-rich plasma (PRP)</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Hematocrit = The proportion of blood volume occupied by red blood cells Fibrinolysis = The process of clot dissolution Platelet-Rich Plasma = Plasma with a high concentration of platelets Antiplatelet Antibody = An antibody that targets platelets</p> Signup and view all the answers

    What does clot retraction indicate?

    <p>The number and quality of platelets, fibrinogen concentration, fibrinolytic activity, and packed red cell volume.</p> Signup and view all the answers

    Match the components with their corresponding effects:

    <p>Prostaglandin E = Blocks platelet aggregation Bleeding time test = Measures platelet adhesion Aspirin = Induces functional defect in platelets Clot retraction = Indicates clot stability</p> Signup and view all the answers

    Study Notes

    Thrombopoiesis and Platelet Structure

    • Platelets (2-4 μm in diameter; larger in disease) are cytoplasmic fragments from megakaryocytes.
    • Megakaryocytes, the largest bone marrow cells, can reach up to 160 μm in size and have high ploidy values (4n, 8n, 16n, 32n).
    • Thrombopoietin, produced by the liver and kidneys, regulates platelet production, with an average production time of 10 days.
    • Normal platelet count ranges from 150,000 to 450,000 cells/μL, with a lifespan of 7-10 days.

    Platelet Development

    • Megakaryoblasts differentiate from hematopoietic stem cells to form megakaryocytes through synchronous endoreduplication.
    • Each megakaryocyte produces approximately 1,000-5,000 platelets.
    • Under normal circumstances, up to one-third of platelet production is trapped in the spleen, increasing to 90% during splenomegaly.

    Platelet Morphology and Function

    • Inactively circulating platelets have a discoid shape maintained by a microtubular cytoskeleton.
    • The external glycocalyx contains plasma proteins and glycoprotein receptors essential for platelet adhesion and aggregation.
    • Platelets possess a canalicular system for transporting clotting factors, facilitating secretion of granule contents during activation.

    Granules in Platelets

    • Platelets contain three types of granules: alpha granules, dense granules, and lysosomes.
    • Alpha granules store factors like platelet-derived growth factor, fibrinogen, and von Willebrand factor.
    • Dense granules contain serotonin, ADP, ATP, and calcium; lysosomes hold hydrolase enzymes.
    • Release of granule contents occurs through internal contraction and is essential for hemostasis.

    Hemostasis Functions

    • Platelets play a critical role in hemostasis by forming a primary plug, releasing procoagulant molecules, and providing a surface for coagulation reactions.
    • Platelet adhesion occurs within 1-2 minutes post-vessel injury, aided by ADP which increases adhesiveness.
    • Glycoprotein IIb/IIIa receptors mediate interaction with fibrinogen, facilitating platelet cohesion.

    Platelet Aggregation

    • A multistep process involving distinct receptors and ligands occurs during platelet aggregation, influenced by blood flow conditions.
    • Aggregation can be triggered by collagen, thrombin, and other agents.
    • Aggregates reinforced by fibrin become thrombi; aspirin can lead to prolonged bleeding time by inhibiting aggregation.

    Laboratory Assessment of Platelets

    • Quantitative platelet determination can be achieved through electronic counters or manual methods, estimating normal levels based on microscopy.
    • Qualitative assessment is necessary if bleeding history suggests normal platelet counts.
    • Bleeding time indicates platelet functionality and integrity, increasing significantly below certain platelet thresholds.

    Additional Platelet Tests

    • Clot retraction reflects platelet number and quality, fibrinogen levels, and hematocrit.
    • Aggregation tests using agents like thrombin measure the platelet-rich plasma's cloudiness to evaluate function.
    • Antiplatelet antibody assays may detect antibodies against platelets, particularly in immune thrombocytopenia cases.

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    Description

    This quiz focuses on the structural and functional aspects of platelets, including their development from megakaryocytes. You will explore the morphological features of platelets and their role in responding to vascular damage. Test your knowledge on the formation and components of mature platelets.

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