Haemostasis

Question 1

what is haemostasis

Answer 1

process of blood clot formation at the site of vessel injury

Question 2

what is the response of a vessel to injury

Answer 2

vasoconstriction – reduced blood flow to the injured area

Question 3

what happens in primary haemostasis

Answer 3

formation of the platelet plug

Question 4

what happens in secondary haemostasis

Answer 4

formation of the fibrin clot

Question 5

components of normal haemostatic system

Answer 5

formation of platelet plug (primary)
formation of fibrin clot (secondary)
fibrinolysis
anticoagulant defences

Question 6

how are platelets formed

Answer 6

budding from megakaryocytes in the bone marrow

Question 7

platelet lifespan

Answer 7

7-10 days

Question 8

how is the platelet plug formed

Answer 8

endothelial (vessel wall) damage exposes collagen and releases Von Willebrand Factor (VWF)
Platelet membrane receptor glycoprotein Ib (Gplb) has VWF receptors
Platelet adhesion at the site of injury
there is then secretion of chemicals from the platelets which leads to aggregation of platelets at the site of injury

Question 9

what do platelets release at the site of injury

Answer 9

ADP
serotonin
thromboxane A2
fibrinogen

Question 10

why might formation of a platelet plug fail

Answer 10

vascular
- loss of collagen in vessel walls makes it easier for them to break down

platelets

• reduced numbers
• reduced function

VWF
- reduced levels or not functioning

Question 11

consequences of failure platelet plug formation

Answer 11

spontaneous bruising + purpura

mucosal bleeding

• epistaxis
• GI
• Conjunctival
• menorrhagia

intracranial haemorrhage

retinal haemorrhage

Question 12

when is menorrhagia a key presenting complaint

Answer 12

von willebrand problems

Question 13

screening test for primary haemostasis

Answer 13

platelet count

Question 14

what 3 things are needed for formation of a platelet plug

Answer 14

platelets
VWF
collagen in vessel wall

Question 15

how is a fibrin clot formed

Answer 15

1. tissue factor is released from damaged vessel walls
   this binds the first clotting factor – factor 7
2. this then activates clotting factors 5 and 10
3. factors 5 and 10 turn prothrombin into thrombin
4. thrombin then turns fibrinogen into fibrin
5. thrombin also activates fact 8 and 9
6. they then activate more clotting factor 5 and 10
7. feedback loop established

Question 16

what step in fibrin clot formation is called initiation

Answer 16

when TF is released and activates factor 7

Question 17

what step in fibrin clot formation is called is called propagation

Answer 17

clotting factor 5 and 10 converting prothrombin into thrombin

Question 18

what step in fibrin clot formation is called amplification

Answer 18

thrombin activation factor 8 and 9 which go on to activate more 5 and 10

Question 19

causes of fibrin clot failure

Answer 19

single clotting factor deficiency
- e.g. haemophilia (factor 8 deficiency)

multiple clotting factor deficiency
- e.g. disseminated intravascular coagulation

increased fibrinolysis
- part of complex coagulopathy

Question 20

how does fibrinolysis occur

Answer 20

plasminogen converted to plasmin by tissue plasminogen activator (tPA)

plasmin converts fibrin to fibrin degradation products (FDP)

Question 21

how is FDP measured

Answer 21

d-Dimers

Question 22

screening tests for fibrin clot formation

Answer 22

prothrombin time (PT)

activated partial thromboplastin time (APTT)

Question 23

what does prolonged PT suggest

Answer 23

problem with TF or factor 7

Question 24

what drug can increase PT time

Answer 24

warfarin

Question 25

what does prolonged APTT suggest

Answer 25

problem with factor 8 or 9

Question 26

what drug can increase APTT time

Answer 26

heparin

Question 27

how does anti-coagulation occur

Answer 27

anti-thrombin 3 binds to thrombin + switched off TF, factor 7, factor 5 and 10, factor 8 and 9

Question 28

what is protein C and protein S

Answer 28

co factors activated by thrombin that switched off factor 5, 10 and 8