Physiology Chapter 5: Hemostasis
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Questions and Answers

What is the normal range of platelets per microliter of blood?

  • 100,000-200,000
  • 200,000-500,000
  • 150,000-400,000 (correct)
  • 300,000-600,000
  • What is the purpose of the smooth muscle contraction in the blood vessel spasm stage of hemostasis?

  • To increase blood flow to the wound site
  • To reduce blood flow to the wound site (correct)
  • To release thrombin
  • To stimulate platelet activation
  • What is the function of Von Willebrand factor (VWF) in platelet plug formation?

  • To inhibit platelet secretion
  • To stimulate platelet activation
  • To facilitate platelet adhesion (correct)
  • To release calcium ions
  • What is the term for the stoppage of bleeding?

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

    Which of the following is NOT a stage of hemostasis?

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

    What happens when ADP binds to platelets?

    <p>They are activated and aggregate</p> Signup and view all the answers

    What is the name of the factor released by platelets that stimulates smooth muscle contraction in blood vessels?

    <p>Thromboxane A2</p> Signup and view all the answers

    What is the approximate diameter of a platelet?

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

    What is the result of Stage 3 Blood Coagulation?

    <p>Formation of a blood clot</p> Signup and view all the answers

    What is the mode of action of Warfarin in decreasing blood clotting?

    <p>By blocking an enzyme that reactivates vitamin K1</p> Signup and view all the answers

    What is the function of Streptokinase?

    <p>To activate plasminogen</p> Signup and view all the answers

    What is the intrinsic pathway also known as?

    <p>Contact activation pathway</p> Signup and view all the answers

    What activates factor X in the extrinsic pathway?

    <p>Tissue thromboplastic</p> Signup and view all the answers

    What is the normal range for bleeding time?

    <p>2-6 min</p> Signup and view all the answers

    What is the normal range for clotting time?

    <p>5-11 min</p> Signup and view all the answers

    What is the function of platelet-derived growth factor?

    <p>Stimulating smooth muscle cells and fibroblasts</p> Signup and view all the answers

    What happens to the blood clot after it forms?

    <p>It retracts and pulls the edges of a broken blood vessel together</p> Signup and view all the answers

    What is the partial thromboplastin time (PTT) used for?

    <p>To test the intrinsic and common pathway</p> Signup and view all the answers

    What is the difference between serum and plasma?

    <p>Serum is the liquid that remains after the blood has clotted, while plasma is the liquid that remains when clotting is prevented</p> Signup and view all the answers

    What triggers the clotting cascade?

    <p>Cellular damage and blood contact with foreign surfaces</p> Signup and view all the answers

    How many separate steps are involved in the clotting cascade?

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

    What is the function of plasmin in the body?

    <p>It digests blood clots</p> Signup and view all the answers

    What is the role of fibrin in preventing blood clotting within normal vascular systems?

    <p>It absorbs thrombin and prevents the clotting reaction from spreading</p> Signup and view all the answers

    What is a thrombus?

    <p>An abnormal intravascular clot attached to a vessel wall</p> Signup and view all the answers

    What is a common cause of thromboembolism?

    <p>Roughened vessel surfaces associated with atherosclerosis</p> Signup and view all the answers

    What is the result of vitamin C deficiency in the context of blood clotting?

    <p>Lack of stable collagen</p> Signup and view all the answers

    What is the function of heparin in the body?

    <p>It potentiates antithrombin III</p> Signup and view all the answers

    What is the effect of aspirin on platelet activation?

    <p>It reduces platelet activation</p> Signup and view all the answers

    What is the effect of clopidogrel on platelet activation?

    <p>It is an irreversible inhibitor of the ADP receptor on platelet membranes</p> Signup and view all the answers

    Study Notes

    Platelets

    • Formed in bone marrow, with a count of 150-400,000/µl
    • 30% sequestered in spleen, with a diameter of 2-4 µm and a lifespan of 8-12 days, no nucleus
    • Active cytoplasm with enzyme synthesis
    • Membrane receptors for thrombin, ADP, and serotonin
    • Storage of calcium and adhesion proteins (VWF, fibronectin, collagen, fibrinogen)
    • Synthesis of prostaglandins, coat of glycoproteins for adhesion to injured areas
    • Granules containing ADP, serotonin, and ATP, phospholipids for activation of intrinsic pathway
    • α-granules containing fibrinogen, PDGF, VWF, fibronectin, and fibrin stabilizing factor

    Hemostasis

    • Refers to the stoppage of bleeding (hemo = blood, stasis = standing)
    • Three stages: blood vessel spasm, platelet plug formation, and blood coagulation

    Stage 1: Blood Vessel Spasm

    • Triggered by pain receptors, local myogenic spasm, and local release of thromboxane A2 and serotonin
    • Results in smooth muscle contraction in blood vessels to minimize blood flow from the wound site

    Stage 2: Platelet Plug Formation

    • Triggered by exposure of platelets to collagen
    • Results in platelet adhesion, activation, and aggregation to form a plug
    • Steps of platelet plug formation: adhesion, secretion, and aggregation

    Stage 3: Blood Coagulation

    • Triggered by cellular damage and blood contact with foreign surfaces
    • Results in the formation of a blood clot through a series of reactions
    • Two pathways: extrinsic (tissue factor pathway) and intrinsic (contact activation pathway)

    Coagulation Cascade

    • Involves seven separate steps
    • Requires contact with tissue factors external to the blood or exposure to collagen
    • Intrinsic pathway involves factor XII activation
    • Extrinsic pathway involves tissue thromboplastin release from traumatized tissue

    Serum and Plasma

    • Serum: liquid remaining after blood has clotted
    • Plasma: liquid remaining when clotting is prevented with an anticoagulant

    Fate of Blood Clots

    • Plasmin digests blood clots
    • Platelet-derived growth factor stimulates smooth muscle cells and fibroblasts to repair damaged blood vessel walls

    Prevention of Blood Clotting

    • Smooth lining of blood vessels discourages platelet accumulation and clotting factors
    • Fibrin absorbs thrombin and prevents clotting reaction from spreading
    • Cells like basophils and mast cells secrete heparin (an anticoagulant)
    • Dynamic blood flow

    Abnormal Blood Clotting

    • Thrombus: abnormal intravascular clot attached to a vessel wall
    • Emboli: freely floating clots
    • Factors causing thromboembolism include roughened vessel surfaces, imbalances in clotting-anticlotting systems, slow-moving blood, and release of tissue thromboplastin

    Coagulation Defects

    • Vitamin C deficiency: lack of stable collagen (in elderly, alcoholics)
    • Hepatic failure: most clotting factors are made in the liver
    • Vitamin K deficiency: required for prothrombin, VII, IX, and X
    • Hemophilia: excessive bleeding due to deficiency of clotting factors
    • Thrombocytopenia: bleeding from small capillaries and blood vessels due to low platelet count

    Anti-Hemostatic Drugs

    • Heparin: potentiates antithrombin III
    • Aspirin: inhibits thromboxane A2 production and platelet activation
    • Clopidogrel: irreversible inhibitor of ADP receptor on platelet membranes
    • Warfarin: decreases blood clotting by blocking vitamin K epoxide reductase
    • Streptokinase: plasminogen activator

    Tests for Hemostasis

    • Platelet disorder tests: bleeding time (increased in thrombocytopenia)
    • Coagulation disorder tests: clotting time, partial thromboplastin time (PTT), and prothrombin time (PT)

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    Physiology 5 ‘ Hemostasis PDF

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    This quiz covers the physiology of hemostasis, focusing on platelets, their formation, structure, and functions.

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