Haematology Lecture 5: Haemostasis
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Questions and Answers

What is the primary role of the endothelium in haemostasis?

  • To maintain blood flow and respond to vascular injury (correct)
  • To prevent the formation of platelet plugs
  • To encourage blood clotting without any controls
  • To create a barrier for nutrient exchange

    • What is the first stage of blood clotting?

  • Formation of fibrin network
  • Vasoconstriction (correct)
  • Formation of platelet plug
  • Clot retraction

    • Which factor promotes vasodilation during normal endothelial function?

  • Endothelin-1
  • Prostacyclin (correct)
  • Collagen
  • Nitric oxide (correct)

    • What is the result of endothelial damage in terms of vascular response?

    <p>Vasoconstriction due to endothelin-1</p> Signup and view all the answers

    Which of the following correctly lists the stages of blood clotting?

    <p>Vasoconstriction, Formation of platelet plug, Formation of fibrin network, Clot retraction and dissolution</p> Signup and view all the answers

    Why is there a delicate balance in haemostasis?

    <p>To avoid both excessive bleeding and unwanted clot formation</p> Signup and view all the answers

    Which statement about the formation of a platelet plug is true?

    <p>Involves platelet activation after adhesion</p> Signup and view all the answers

    Which substance is released from endothelial cells to inhibit vasodilation?

    <p>Endothelin-1</p> Signup and view all the answers

    What initiates platelet aggregation?

    <p>Damage to endothelium</p> Signup and view all the answers

    What role does von Willebrand factor play in platelet adhesion?

    <p>A bridge between platelets and collagen</p> Signup and view all the answers

    What is released by activated platelets to promote vasoconstriction?

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

    Which process directly follows platelet adhesion during blood clotting?

    <p>Platelet activation</p> Signup and view all the answers

    What is the purpose of the fibrin network in blood clotting?

    <p>To stabilize the platelet plug</p> Signup and view all the answers

    Which steps are involved in the formation of a fibrin mesh from fibrinogen?

    <p>Prothrombinase activates thrombin, which then converts fibrinogen to fibrin</p> Signup and view all the answers

    What is the correct sequence of events in the blood clotting process?

    <p>Vasoconstriction, formation of platelet plug, formation of fibrin network, clot retraction</p> Signup and view all the answers

    What substance released by activated platelets contributes to a positive feedback mechanism during aggregation?

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

    What initiates the extrinsic pathway of blood coagulation?

    <p>Tissue damage exposing Tissue Factor</p> Signup and view all the answers

    Which factors are involved in the prothrombinase complex?

    <p>Activated Factor X and Factor V</p> Signup and view all the answers

    What role does thrombin play in the coagulation process?

    <p>It converts fibrinogen directly to fibrin.</p> Signup and view all the answers

    What essential ion is required for the formation of the fibrin mesh?

    <p>Ca2+</p> Signup and view all the answers

    Which factor is responsible for the cross-linking of fibrin during clot formation?

    <p>Factor XIII</p> Signup and view all the answers

    How does thrombin amplify the clotting process?

    <p>By activating Factor V in the prothrombinase complex.</p> Signup and view all the answers

    What role does calcium play in the activation of clotting factors?

    <p>It is necessary for the activation of some clotting factors.</p> Signup and view all the answers

    Which process follows the formation of a fibrin monomer?

    <p>Polymerization into fibrin fibers</p> Signup and view all the answers

    Which process involves the digestion of fibrin threads?

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

    What is the role of vitamin K in blood clotting?

    <p>It is essential for the activation of various clotting factors.</p> Signup and view all the answers

    What is the primary function of plasminogen activator (tPA)?

    <p>To convert plasminogen to plasmin</p> Signup and view all the answers

    Which mechanism does Antithrombin III utilize to limit blood clotting?

    <p>It inhibits thrombin and other factors.</p> Signup and view all the answers

    What is the effect of Protein C when activated?

    <p>It inactivates factors V and VIII.</p> Signup and view all the answers

    Which of the following conditions is characterized by a deficiency in Factor VIII?

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

    What is the consequence of protein S deficiency in terms of blood clotting?

    <p>It results in hypercoagulation.</p> Signup and view all the answers

    Which statement is true regarding the function of fibrin in blood clotting?

    <p>Fibrin threads stabilize the clot.</p> Signup and view all the answers

    Study Notes

    Haematology Lecture 5: Haemostasis

    • Haemostasis is a delicate balance to prevent blood loss and maintain blood in a fluid state; it also prevents haemorrhage and thrombosis
    • Learning objectives for the lecture include the role of the endothelium in haemostasis, the 4 main stages of blood clotting and clot resolution, details of fibrin mesh formation, mechanisms to limit blood clotting, and disorders of blood clotting.

    Role of Endothelium in Maintaining Blood Flow

    • Intact endothelium promotes vasodilation, releasing prostacyclin and nitric oxide.
    • Damaged endothelium promotes vasoconstriction, releasing endothelin-1.

    4 Stages of Blood Clotting

    • 1. Vasoconstriction: Injury to a blood vessel causes contraction of the smooth muscle of the vessel; this involves myogenic contraction and a change in the balance of endothelial vasodilators and vasoconstrictors. Endothelin-1 inhibits the release of nitric oxide and prostacyclin, reducing blood flow temporarily.
    • 2. Formation of Platelet Plug: This involves platelet adhesion, activation, and aggregation. Initiated by damage to the endothelium exposing platelets to subendothelial collagen. von Willebrand factor acts as a bridge between platelets and collagen. Platelets release ADP, serotonin, and thromboxane A2, promoting vasoconstriction and further platelet activation (positive feedback).
    • 3. Formation of Fibrin Network (Coagulation): Formation of prothrombinase; the intrinsic and extrinsic pathways. Conversion of prothrombin to thrombin. Thrombin catalyses the formation of the fibrin mesh from fibrinogen.
    • 4. Clot Retraction and Dissolution: Clot retraction occurs within minutes to hours. Platelets contain actin and myosin, causing contraction that squeezes out serum and pulls the edges of the vessel together. Fibrinolysis is the breakdown of the clot. Plasminogen is converted to plasmin by tissue plasminogen activator (tPA), a proteolytic enzyme that digests fibrin threads and clotting factors.

    Formation of the Fibrin Mesh

    • Thrombin acts on fibrinogen to form fibrin monomers.
    • Calcium is required for the polymerisation of fibrin monomers into long fibrin fibres.
    • Fibrin-stabilizing factor (Factor XIII) causes fibrin cross-linking. Activated by thrombin and released from platelets.

    Vitamin K and Blood Clotting

    • Vitamin K is essential for blood clotting.
    • It acts as a cofactor for enzymatic modification of some clotting factors, enabling them to bind calcium.
    • Calcium is necessary for the activation of some clotting factors.

    Mechanisms to Limit Blood Clotting

    • 1. Antithrombin III: Inhibits thrombin and other factors at intact endothelium, accelerated by heparin.
    • 2. Protein C Pathway: Thrombomodulin on endothelial cells changes thrombin's activity, activating Protein C. Activated Protein C, with its cofactor Protein S, inactivates factors V and VIII.
    • 3. Tissue Factor Pathway Inhibitor (TFPI): Found attached to the endothelium, and it inhibits Factor X and Factor VII/Factor III complex.

    Some Clotting Disorders

    • Platelet defects (thrombocytopenia) causing multiple bruises and petechiae.
    • Disorders of von Willebrand's disease.
    • Haemophilia (lack of Factor VIII or IX), X-linked recessive, affecting primarily males.
    • Liver disease.
    • Vitamin K deficiency.
    • Hypercoagulation/thrombotic disorders.
    • Protein S deficiency.

    Summary of Main Points

    • Haemostasis involves a delicate balance between pro-coagulant and anticoagulant mechanisms.
    • Clotting is activated when the endothelium is damaged.
    • Platelets are crucial in blood clotting, and thrombin is the central regulator.
    • Vitamin K and calcium are essential for clotting factor activation. Deficiency in either of these, or a factor, can lead to disorders.
    • Deficiency of coagulation factors may cause haemophilia, while deficiency of anticoagulant mechanisms can lead to thrombosis.

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    Description

    This quiz covers key concepts from Haematology Lecture 5, focusing on haemostasis, the role of the endothelium, and the stages of blood clotting. Understand the mechanisms involved in preventing blood loss and maintaining blood fluidity, including disorders of clotting. Brush up on the intricacies of clot formation and resolution.

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