Physiology lecture 4

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Megakaryocytes are...
Large bone marrow cells that platelets bud off.
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What are the three steps of haemostasis?
1) Vascular spasm (blood vessel constriction) 2) Formation of platelet plug 3) Blood coagulation
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What is a vascular spasm?
Smooth muscle layer surrounding cut immediately contracts, slowing blood flow. Damaged cells and platelets release potent vasoconstrictors such as serotonin and ADP. Endothelial surfaces become sticky and adhere to each other
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During a platelet plug what do they platelets stick to?
Stick to exposed tissue eg. collagen. Stick to each other using von Willebrands factor (vWF) --> plasma protein
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The platelets bound to collagen through vWF release... (and what do they cause?)
ADP, 5HT ad thromboxane A2 which causes surface of nearby platelets to become sticky --> adhere to other platelets
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What is the process of blood clotting?
Fibrinogen --------(thrombin)------> Fibrin monomers -----(XIIIa and Ca2+)------> Fibrin polymer
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What pathways stimulate thrombin?
1) Intrinsic-all necessary factors in blood 2) Extrinsic - initiating factor on plasma membrane of cells outside of endothelial blood cell lining (TISSUE DAMAGE)
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Name the two anti-clotting systems.
1) Anti-thrombin 2) Thrombomodulin, proteins C and 5
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What does the anti-thrombin system do? (anti-clotting)
Inhibits many clotting factors (thrombin) - activity is enhanced by HEPARIN (present in endothelial cells)
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What does the thrombomodulin system do? (anti-clotting)
Binds thrombin, eliminates thrombin's coagulant effects, activates protein C. Protein 5 acts as a co-factor for protein C to inactivate Va and VIIIa
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How is the clot dissolved?
Aggregated platelets secrete platelet derived growth factor beta ---> Recruitment of fibroblasts ---> Form scar tissue ---> Clot dissolves by plasmin
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What activates plasmin?
Tissue plasminogen activator (t-PA)
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What are the stages of fibrinolysis?
Plasminogen -------(t-PA)--------> Plasmin -------> Fibrin ------> Soluble fibrin fragments
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What causes the colours of a bruise?
The degradation of Hb to biliverdin, bilirubin and haemosiderin
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Name 2 anticoagulants.
Warfin, Heparin
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What does warfin do?
Inhibits the action of vitamin K (clotting factors II, VII, IX, X all need vitamin K in their synthesis)
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How is heparin given? What does it do?
Given as injection, binds to inhibitor antithrombin II
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What is the bleeding time? How long on average is the bleeding time?
Time taken for formation of platelet plug. 3-10 minutes
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During coagulation tests what is the blood mixed with and why?
Trisodium citrate which removes Ca2+ by chelation
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What are the clot times dependant on? (coagulation tests)
Dependant on addition of CaCl
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What does prothrombin time measure? At what temp. is it done at? What does it have a high concentration of? How is reclassification achieved?
Measure effectiveness of extrinsic and common pathway / 37oC / High concentration of thromboplastin / Add CaCl
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What is the average time for prothrombin time?
11-13.5 seconds
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What does the average partial thromboplastin time measure? What temp. is it done at? What is used as the surface activator?
Measures effectiveness of intrinsic and common pathway / 37oC / Kaolin
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What is the average time for APTT time?
25-35 seconds
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What does thrombin time measure?
Measure adequacy of the common pathway ie. fibrinogen ---> fibrin catalysed by thrombin
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What is the average time for thrombin time?
12-14 seconds
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Other cards in this set

Card 2

Front

What are the three steps of haemostasis?

Back

1) Vascular spasm (blood vessel constriction) 2) Formation of platelet plug 3) Blood coagulation

Card 3

Front

What is a vascular spasm?

Back

Preview of the front of card 3

Card 4

Front

During a platelet plug what do they platelets stick to?

Back

Preview of the front of card 4

Card 5

Front

The platelets bound to collagen through vWF release... (and what do they cause?)

Back

Preview of the front of card 5
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