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3 Haematology > Intro to Haemostasis > Flashcards

Intro to Haemostasis Flashcards

1
Q

what is Haemostasis

A

the arrest of bleeding and maintenance of vascular patency

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2
Q

what is needed for homeostasis

A

a permanent state of readiness

a prompt response

a localised response

protection against unwanted thrombosis

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3
Q

what happens in the normal homeostatic system

A

formation of a platelet plug

formation of a fibrin clot

fibrinolysis

anticoagulant defences

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4
Q

how and where are platelets formed

A

in the bone marrow by ‘budding’ from megakaryocytes

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5
Q

what is the structure of a platelet

A

small anucleate discs

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6
Q

what is the lifespan of a platelet

A

7-10 days

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7
Q

how are platelets activated

A

endothelial (vessel wall) damage exposed collagen to the blood and also releases Von Willebrand Factor (VWF)

this causes passing platelets to stick to the side of injury as they have VWF receptors (glycoprotein IB)

platelets then secrete chemicals causing aggregation of platelets at the site of injury (attract more and make them all stick together)

this forms a platelet pug

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8
Q

what causes the failure of platelet plug formation

A

Vascular problems

Platelet problems

  • reduced number (thrombocytopenia)
  • reduced function

Von Willebrand Factor problems (low or absent)

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9
Q

what happens if a platelet plug is not formed (presentation in failure of primary haemostasis)

A

spontaneous bleeding and purpura

mucosal bleeding

  • epistaxes
  • gastrointestinal
  • conjunctival
  • menorrhagia

intracranial haemorrhage

retinal haemorrhages

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10
Q

how do you screen for primary Haemostasis problems

A

platelet count

-no other simple screening test

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11
Q

what is primary haemostats

A

formation of a platelet plug

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12
Q

what is secondary Haemostasis

A

formation of a fibrin clot (more stable than platelet plug)

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13
Q

how are fibrin clots formed (v basic)

A

conversion of prothrombin to thrombin

thrombin causes the conversion of fibrinogen to fibrin

fibrin forms a mesh for proteins to stick to

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14
Q

where are the clotting factors used for secondary Haemostasis produced

A

liver

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15
Q

what clotting factors are vitamin K dependent

A

II, VII, VIII, X

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16
Q

what two pathways lead to fibrin production

A

Extrinsic pathway

Intrinsic pathway

17
Q

what is the extrinsic pathway

A

Tissue factor released from damaged vessels

tissue factor binds to and activated factor 7

TF-factor 7 complex caused factor X to become Xa

X-Xa leads onto the common pathway

18
Q

what is the intrinsic pathway

A

not as important in fibrin production but amplifies response

exposed collagen at damaged side activates factor XII which starts a cascade

XII-XIIa
XI-XIa
IX-IXa

IXa binds to factor VIIIa

Activates factor X

this triggers the common pathway

19
Q

what happens if the intrinsic pathway doesn’t work

A

bleeding into muscles and joints

20
Q

what is the common pathway

A

the pathway that actually produced the thrombin

IXa-XIIa (intrinsic) and TF-7a complexes both activated factor X starting the cascade

X-Xa - this activates factor II
Prothrombin - thrombin (II-IIA)
fibrinogen - fibrin

II also activated IIX in the intrinsic pathway to help stabilise the clot

21
Q

what does prothrombin time measure

A

the time for the extrinsic pathway to go from TF to TF-7 complex

22
Q

what does activated partial prothrombin time measure

A

the time for the intrinsic pathway to go from facts 12 to IXa-VIIIa

23
Q

what does thrombin time measure

A

time for the common pathway to go from factor 10 to the production of fibrin

24
Q

what causes a failure in fibrin clot formation

A

Single clotting factor deficiency eg. haemophilia (hereditary)

Multiple clotting factor deficiencies (disseminated intravascular coagulation - acquired)

Increased fibrinolysis (complex coagulopathy)

25
Q

how is fibrin broken down in fibrinolysis

A

Tissue plasminogen activator converts plasminogen to plasmin

plasmin caused fibrin to be broken down into fibrin degradation products

26
Q

what happens if secondary haemostats (fibrin clot formation) does not work

A

no characteristic syndrome

may be combined primary/secondary failure

bleeding depends on:

  • single/multiple abnormalities
  • what factors are involved
27
Q

questions to ask in bleeding disorders history

A 
bleeding/bruising 
duration 
previous surgery/dental extractions 
drug history 
family history 
examination
28
Q

what do anticoagulants do

A

interrupt fibrin clot formation

29
Q

what do anti-platelets do

A

interrupt platelet plug formation

30
Q

what are some naturally occurring anticoagulants

A

Serine protease inhibitors (anti-thrombin)

Protein C and protein S

31
Q

what is a thrombophilia

A

deficiency of naturally occurring anticoagulants

increased tendency to develop venous thrombosis

3 Haematology (25 decks)

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