2. INTRODUCTION
• Hemostasis is a regulated process by which blood is
maintained in liquid state inside the vessels, yet arrests
bleeding at the site of vascular injury by forming a
hemostatic clot.
• Components of normal hemostasis : platelets, blood vessel
wall (endothelium), coagulation system, fibrinolytic
system and coagulation regulatory system.
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3. HEMOSTASIS
Mechanisms
(I) Vasoconstriction of blood vessels
(II) Exposure of collagen
(III) platelet plug formation
(IV) Blood coagulation (fibrinogen fibrin)
(V) Fibrinolysis to dissolve the clot
(VI) coagulation regulatory system
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7. PLATELETS
• Platelets are produced from bone marrow precursors known
as megakaryocytes.
• Regulation of megakaryocyte differentiation and
maintenance of peripheral blood platelet numbers are
primarily regulated by thrombopoietin (TPO).
• Normal platelet count ranges from 150–400 × 10 9 /L and it
has a normal life span of 8-10 days.
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9. Role of Platelets in Hemostasis
• Form the primary hemostatic plug.
• Release platelet activating and procoagulant
molecules.
• Provide a procoagulant surface for the activation of
coagulation system.
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14. • Please watch this animation for a better understanding of
primary homeostasis:
• Iranian users:
• https://s16.picofile.com/file/8414577084/Platelet_Activation_a
nd_Factors_for_Clot_Formation_2.mp4.html
• Other usres:
• https://www.youtube.com/watch?v=R8JMfbYW2p4
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15. Hemostatic Process
Coagulation Cascade
• to stabilize and reinforce the weak platelet plug
• fibrinogen → fibrin
• 3 main steps:
1. formation of prothrombin activator
2. conversion of prothrombin into thrombin
3. conversion of fibrinogen to fibrin
When procoagulant clotting factor becomes activated, it is designated by a lower-case letter ―a‖ after the numerical.
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