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haematology > haemostasis > Flashcards

haemostasis Flashcards

1
Q

the vessel wall is lined by endothelium which in normal conditions prevent what?

A

platelet adhesion and thrombus formation

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2
Q

injury to vessels causes

A

reflex vasoconstriction

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3
Q

endothelial damage results in

A

loss of antithrombic properties, activation of platelets and coagulation and inhibition of fibrinolysis

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4
Q

3 steps that occur to platelets after endothelial damage is?

A
  1. platelet adhesion
  2. platelet activation
  3. platelet aggregation
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5
Q

platelet adhesion - escaping platelets come into contact w and adhere to?

A

collagen and subendothelial bound VWF
-> glycoprotein lb does this
-> activates platelet prostaglandin synthesis

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6
Q

in response to platelet prostaglandin synthesis - platelet dense bodies release what?

A
  • ADP
  • serotonin
  • and other factors
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7
Q

platelet activation - release of ADP leads to a conformational change in fibrinogen receptor, on surface of adherent platelets, allowing it to bind to?

A

fibrinogen

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8
Q

fibrinogen is what?

A
  • a dimer
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9
Q

as fibrinogen is a dimer it can form a direct bridge between platelets thus causing?

A

platelet aggregation
-> and a platelet plug is formed

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10
Q

what is haemostasis?

A
  • arrest of bleeding and maintenance of vascular patency
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11
Q

release of serotonin and TXA2 from platelets cause what?

A

vasoconstriction of vessels

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12
Q

release of what induces platelet aggregation and formation of a platelet plug?

A
  • ADP
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13
Q

coagulation pathway is stimulated and leads to formation of?

A
  • fibrin
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14
Q

fibrin strands are cross linked by factor?

A

XIII

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15
Q

what does cross-linked fibrin do?

A
  • stabilizes haemostatic plug by binding platelets and red cells
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16
Q

coagulation involves a series of enzymatic reactions that lead to conversion of soluble plasma fibrinogen to

A
  • fibrin based clot
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17
Q

fibrinogen and prothrombin are referred to what factors respectively?

A
  • I and II
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18
Q

factors are synthesised in what part of the body?

A
  • liver
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19
Q

what are 2 co-factors?

A
  • V and VIII
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20
Q

coagulation pathway is composed of 3 pathways which are?

A
  • intrinsic and extrinsic pathways and common pathways
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21
Q

secondary haemostasis refers to?

A
  • stabilisation of activated platelets due to actions of strands of fibrin - these generate a ‘stable mesh’ the main component in a thrombus (clot)
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22
Q

fibrin is converted from its precursor fibrinogen by ?

A

thrombin
- and is end product of chain of reactions that make up the coagulation cascade

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23
Q

extrinsic pathway is initiated by ?

A
  • tissue factor
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24
Q

where is tissue factor found?

A
  • expressed on surface of many cells outside blood vessels
  • when endothelium is damaged, TF, comes into contact w blood and combines w factor VII to form a complex -> Xa triggering common pathway
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25
Q

TF combines w factor VII to form a complex activating what factor?

A
  • Xa -> thus triggering common pathway
26
Q

common pathway begins w activation of?

A
  • factor X
    via either extrinsic or intrinsic pathway
  • final stage of coagulation cascade
27
Q

what is final stage of coagulation cascade?

A
  • formation of thrombin and fibrin
28
Q

factor Xa combines w ? to convert prothrombin into thrombin

A
  • factor V, platelet membrane phospholipids and Ca2+ ions
29
Q

thrombin converts fibrinogen into?

A
  • fibrin strands which form an important structural component of a thrombus
30
Q

thrombin activates many parts of the coagulation cascade via positive feedback loop through what pathway?

A
  • intrinsic pathway
31
Q

the intrinsic pathway can be activated by?

A
  • surface contact - when damage to vascular endothelium leads to exposure of clotting factors -> negatively charged subendothelial
  • also within blood vessels, thrombin generated from prev activation of extrinisic pathway also activates intrinsic pathway
32
Q

instrinic pathway also leads to amplification of what substance?

A
  • thrombin - creating positive feedback loop
33
Q

intrinsic pathway: surface contact activates?

A
  • factor XII
34
Q

intrinsic pathway: factor XIIa activates factor?

A
  • factor XI
35
Q

intrinsic pathway: factor XIa combines w factor VIIIa, platelet membrane phospholipid and Ca2+ ions to activate?

A
  • factor X
36
Q

intrinsic pathway: factor Xa activates common pathway generating more?

A
  • thrombin
37
Q

function of thrombin?

A
  • fibrin generation
  • intrinsic pathway activation: thrombin initiates intrinsic pathway
  • factor XIII activation - XIIIa (fibrin stabilising factor) - cross-links fibrin - to generate fibrin mesh - surrounding platelets and stopping bleeding
  • platelet activation
  • regulation of clot formation
38
Q

what initiates common pathway?

A
  • factor Xa
39
Q

components of extrinsic pathway?

A
  • TF
  • factor VII (7)
40
Q

components of intrinsic pathway?

A
  • factor XII (12)
  • factor XI (11)
  • factor IX (9)
  • factor VIII (8)
  • platelet membrane phospholipids
  • Ca2+ ions
41
Q

components of final common pathway?

A
  • factor X (10)
  • factor V (5)
  • prothrombin
  • platelet membrane phospholipids
  • Ca2+ ions
  • fibrinogen
42
Q

what are some proteins that inhibit coagulation cascade when enough thrombin has been produced?

A
  • protein C
  • protein S
  • antithrombin
  • tissue factor pathway inhibitor
43
Q

protein C is produced in response to thrombin binding to?

A
  • thrombomodulin on vascular endothelium
44
Q

thrombin + thrombomodulin (receptor) leads to activation of?

A
  • protein S
    -> protein S breaks down factors Va (5) and VIIIa (8) in neg feedback loop
45
Q

antithrombin is produced where and what is its function?

A
  • produced by liver and destroys factors XIa (11), Xa (10) and thrombin
46
Q

heparin and fondaparinux enhance natural effects of what protein?

A
  • antithrombin
47
Q

TFPI (tissue factor pathway inhibitor) binds to and inactivates?

A
  • factor VIIa (7)
  • factor Xa (10)
48
Q

warfarin is a vit K antagonist which prevents synthesis of?

A
  • vit k dependent clotting factors - II (2 - prothrombin), VII (7), IX (9), and X (10)
49
Q

LMWH is prescribed alongside warfarin when tx is initiated why?

A
  • as vit K is also required for synthesis of natural anticoagulants protein C and protein S so warfarin may inhibit their production initially
50
Q

when can LMWH be stopped?

A
  • once INR is at target range
51
Q

PT time measures time taken for fibrin to form via what pathway?

A
  • extrinsic pathway
    PT - 9-12 secs
52
Q

Activated thromboplastin time measures time taken for fibrin to form via which pathway?

A
  • intrinsic pathway
    APTT - 23-38 secs
    measuring 12, 11, 9, 8, 10, 5, prothrombin and fibrinogen
53
Q

causes of prolonged PT > 12 secs

A
  • DIC
  • Vit K deficiency
  • chronic liver disease
54
Q

INR monitors levels of anticoagulation in patients on which drug?

A
  • warfarin
55
Q

causes of prolonged APTT > 38 secs?

A
  • DIC
  • clotting factor deficiencies - haemophilia A or B
  • lupus anticoagulant
  • Von Willebrand’s disease
56
Q

lupus anticoagulant can prolong APTT test but do not increase what?

A
  • tendency of a patient to bleed
57
Q

dysfunction of coagulation cascade can be caused by what medical conditions?

A
  • haemophilia - A (8), B (9), C (11)
  • chronic liver disease
  • factor V leiden
58
Q

extrinsic and intrinsic pathway both result in activation of factor ?

A
  • X - which leads to conversion of prothrombin to thrombin
59
Q

thrombin, converts fibrinogen -> fubrin and triggers activation of factor ?

A
  • XIII (8) to cross link fibrin strands and stabilise clot
60
Q

stable clot is formed by ?

A
  • activated platelets, fibrin and factor XIIIa

haematology (3 decks)

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