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15 Cards in this Set
- Front
- Back
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What are the functions of platelets? |
-Maintain vessel integrity - Granules contain cytokines to promote intercellular adhesion -Form primary hemostatic plug -Provide surface for coagulation factors -Helps vasculature to heal - PDGF and Beta-thromboglobulin |
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What are the steps in making the primary plug? |
-Tissue Injury -Platelet Adhesion -Activation/Shape Change -Secretion -Aggregation -Primary plug forms |
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What are the characteristics of Tissue Injury? |
-Normally anti-thrombotic - negatively charged - Heparin molecules - Produce natural coagulation inhibitors |
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What happens if tissue injury occurs? |
- Vasoconstriction - lowers blood flow to prevent blood from leaking out - brings platelets closer to vessel surface - Becomes thrombogenic - von Willebrand factor (vWF) - Tissue Factor - Collagen |
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What happens in Platelet Adhesion? |
-Platelets attach to exposed collagen -Need vWF to & GPIb/IX to do this - von Willebrand factor - Forms a layer of platelets - Adhesion triggers the activation process
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Describe von Willebrand Factor and it's role in Platelet Adhesion... |
von Willebrand Factor - Protein synthesized by endothelial cells (and megakaryocytes) - Receptors for GPIb/IX and collagen - Bridge between platelet and collagen - Stored in Weibel-Palade bodies in endothelial cells |
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What is Platelet Activation triggered by? |
- Triggered by Adhesion -Signals many changes in platelets - Shape, receptors, and biochemistry - GPIIb/IIIa receptors are activated for the binding of fibrinogen - Platelets can secrete their granule contents |
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What are agonists? |
- Substances that induce activation - collagen, thrombin, ADP, epinephrine, serotonin, thromboxane A2 |
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What happens during shape change (in platelet activation)? |
- Organelles move to center - Granules move closer to OCS - Actin polymerization - More GPIIb/IIIa move to surface so fibrinogen can bind |
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What happens during Actin Polymerization? |
-Transforms the platelets to have pseudopods -Allows for greater surface area for reactions |
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What is Thromboxane A2? |
- Formed by the hydrolysis of arachidonic acid - (with cyclooxygenase & thromboxane synthase) -Labile compound - Quickly converts to thromboxane B2 (inactive) |
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What are the functions of Thromboxane A2? |
-Stimulates secretion of platelet granules -Enhances vasoconstriction -Platelet agonist |
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What happens during secretion? |
-Release of platelet granule contents -Occurs simultaneously with aggregation -Requires ATP |
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What happens during the process of Platelet Aggregation? |
-More platelets pile on -Fibrinogen binds to GPIIb/IIIa -More platelets bind to fibrinogen -Those platelets become activated -Primary aggregation - Platelets bind loosely at first -Secondary aggregation - Platelets that bind release their own granules/agonists |
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What happens when the Primary Platelet Plug is formed? |
-Seals injured area -Bleeding stops -Relatively unstable - it can be dislodged -Ready for secondary hemostasis to begin |
