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48 Cards in this Set

  • Front
  • Back
what substances do endothelial cells secrete during haemostasis?
von Willebrand Factor, prostacyclin, tissue plasminogen activator
t/f... at site of vessel injury, vasodilation occurs
false, vasocnstriction occurs to control the initial rate and volume of bleeding
how do circlating platelets adhere to exposed subendothelial matrices?
via vWF
what activates prothrombin to thrombin?
factor Xa
what does thrombin do?
converts fibrinogen to fibrin
what is the half-life of factor VIII?
9-18 hours
t/f... vWF is the largest known soluble protein
true
which are the vitamin K dependent coagulation factors?
factors II, VII, IX and X as well as protein C and protein S
what is the normal lifespan of platelets?
7-10 days
t/f... platelets contain a nucleus
false
how does lysis of fibrin occur?
plasminogen is activated to plasmin by t-PA and cleaves fibrin degradation products
which factor initiates the extrinsic pathway?
factor VII
which clotting factors are produced in the liver?
factor II, V, VII, IX, X, fibrinogen
where is vWF synthesised?
endothelial cells and megakaryocytes
what are the two roles of vWF in clotting?
assists in initial adhesion of platelets to damaged endothelium and stabilises factor VIII in the circulation
what is the half life of factor VII?
4-6 hours
what is the half-life of prothrombin?
72 hours
what is the half life of protein C?
12-16 hours
why is there an initial period of potential hypercoaguability when warfarin treatment is begun?
the level of protein C falls before levels of factors X, II and IX have fallen
what Factor VIII level do patients with severe haemophilia have?
1% or less
what stabilises factor VIII in the circulation?
vWF
what is the inheritance of haemophilia?
x-linked recessive
what is the inheritance of von Willebrand's disease?
autosomal dominant
t/f... factor VIII may be reduced in vWD?
true
which of the haemophilias is more common?
heamophilia A (4 times as common as haemophilia B)
what does prothrombin time (PT) test?
extrinsic pathway i.e. factors II, V, VII, X
what tests the intrinsic pathway?
activated partial thromboplastin time (APTT) - tests factors VIII, IX, XI, XII, X
which times will be prolonged with heparin administration?
APTT and TT but not PT
are petechiae more common in clotting disorders or platelet dysfunction?
platelet dysfunction or thrombocytopenia
what is Lyonisation?
skewed X inactivation
what percentage risk does the son of a female carrier of haemophilia have of being affected?
50%
what fraction of cases of haemophilia are a result of new mutations?
approximately 1/3
t/f... the factor VIII gene is expressed in the bone marrow, lymphocytes and endothelial cells
false, it is expressed in the liver, spleen, lymph nodes and other tissues
at what platelet count does spontaneous bleeding occur?
<20 x 10^9/L
what do blood vessels release when injured causing vasoconstriction?
endothelin
which substances released by endothelium inhibit platelet adhesion?
prostacyclin, EDRF (NO), t-PA
what surface is required for coagulation?
phospholipid surface (also need calcium and activator e.g. tissue factor)
which coag factor initiates the extrinsic pathway?
VII
which coag factor initiates the intrinsic pathway?
XII
how does protein C inhibit coagulation?
turns off the two cofactors (V and VIII)
where does bleeding due to platelet disorders occur?
mucosal surfaces and skin
which type of vWD is autosomal recessive?
type III
what fraction of platelets are in the spleen?
1/3
why is splenomegaly accompanied by thrombocytopenia?
platelets sequestered in the spleen
what percentage of children with acute immune thrombocytopenic purpura will develop chronic immune thrombocytopenic purpura?
5-10%
what percentage of Haemophilia A is due to an inversion of gene from intron1-22?
50%
how is haemophilia A treated?
recombinant factor VIII
why does liver disease cause bleeding problems
impaired synthesis of clotting factors, thrombocytopenia, increased fibrinolysis, platelet dysfunction, dysfibrinogenaemia