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23 Cards in this Set
- Front
- Back
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What is the definition of a thrombus?
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Platelet plug and Fibrin Clot
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What 3 things occur in response to vascular injury?How long is each?
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Vasoconstriction
Primary hemostasis-plug formation, few secs Secondary hemostasis-fibrin clot, few minutes |
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What are the 3 types of granules in platelets? Contents?
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Dense granules- Ca and ADP
alpha granules- vwF, Fibrinogen, Factor V, serotonin, PDGF Dense tubular system-like ER, filled with Ca++ |
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How are platelets regulated and kept in the quiscent state?
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Endothelial cell secrete PGI2(vasodilation, plug inhibition)
which binds Gs and increases camp. cAMP causes dense tubular systems to remove Ca=low IC calcium so remains inactive |
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What are the 5 stages of primary hemostasis?
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Adhesion
Activation Secretion\degranulation Shape change Aggrigation |
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How can platelets be activated?
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autocrine TXA2 or Thrombin or several other agonists like epinephrine that initiate a Gq cascade
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What occurs with plug formation agonist with respect to signalling cascade?
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Gq activation>>IP3 and DAG>>increased Calcium>>PLA cleavage>>AA>>TXA2 formation
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What initiated the degranulation phase?
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Formation of TXA2 during activation causes secretion of all platelets granules
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How does degrenulation aid furthur platelet aggrigation? What drug inhibits this?
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ADP in dense granules stimulates aggrigation. Plavix is a ADP receptor antagonist
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How does degranulation aid shape change?
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Secretion adds 60% more phospholipids, increasing surface area leading to more flexibility
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What causes shape change?
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the increase in calcium during activation activates MLC-P(myosin light chain proteins) and causes actin contraction
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What changes occur to platelet during shape change?
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GPIIb\IIIa is exposed on the platelets, as is phosphatidyle serine. This makes it more negative and promotes binding of factor VIII(tenase complex) and factor V(prothrombinase complex)
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What occurs during aggregation phase of primary hemostasis?
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GpIIb\IIIa that were flipped out can bind to fibrinogen and link platelets together
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What causes shape change?
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the increase in calcium during activation activates MLC-P(myosin light chain proteins) and causes actin contraction
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What changes occur to platelet during shape change?
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GP1B\IIIa is exposed on the platelets, as is phosphatidyle serine. This makes it more negative and promotes binding of factor VIII(tenase complex) and factor V(prothrombinase complex)
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What occurs during aggregation phase of primary hemostasis?
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GpIIb\IIIa that were flipped out can bind to fibrinogen and link platelets together
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What part of fibrinogen binds to GPIIB\IIIa?
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RGD motifs of fibrinogen
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What is the clinical use of the drug integrellin?
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Has and RGD motif that binds activated platelets and prevents aggrigation by acting like fibrinogen
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Which COX synthesizes TXA2? Which synths PGI2?
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COX1-TXA2
COX2-PGI2 |
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Why does low does asprin therapy inhibit platelet formation?
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Since platelets lack nucleus they cannot overcome the loss of COX1 to sythesize TXA but endothelial cells can so they make more COX2 and hence PGI2 and inhibit plug formation
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How does adhesion occur in response to vascular injury?
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Exposed collagen binds to vwF, shear forces change conformation of vwf\collagen complex so they may bid to GP1B\IX on platelets. NOTICE IX not activated
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how does vwF affect factor VIII?
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increases half life
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Why are arterial thrombi more full of platelet plugs?
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Because of the high shear forces that favor their formation
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