Haemostasis

Question 1

What is haemostasis?

Answer 1

the arrest of bleeding and maintenance of vascular patency

Question 2

What are the components of haemostasis?

Answer 2

platelet plug formation
fibrin clot formation
fibrinolysis
anticoagulant defences

Question 3

What is primary haemostasis?

Answer 3

platelet plug formation

Question 4

What is secondary haemostasis?

Answer 4

fibrin clot formation

Question 5

How are platelets formed?

Answer 5

in bone marrow by ‘budding’ from megakaryocytes

Question 6

What is the life span of platelets?

Answer 6

7-10 days

Question 7

Describe primary haemostasis.

Answer 7

1 - endothelial damage exposes collagen
2 - releases von willebrand factor (and other proteins) to which platelets have receptors
3 - platelet adhesion to site of injury
4 - secretion of prothrombotic chemicals –> aggregation of platelets at site of injury, forming platelet plug

Question 8

What can cause failure of the platelet plug?

Answer 8

vascular problems
vWF problems
platelet problems - reduced number or function

Question 9

What are the consequences of failure of the platelet plug?

Answer 9

spontaneous bruising and purpura
retinal haemorrhage
mucosal bleeding - petechiae

Question 10

What tests can be used to screen primary haemostasis?

Answer 10

platelet count

Question 11

What can cause failure of the fibrin clot?

Answer 11

increased fibrinolysis
single clotting factor deficiency e.g. haemophilia
multiple clotting factor deficiencies e.g DIC

Question 12

What activates formation of the fibrin clot?

Answer 12

TF (tissue factor)

Question 13

What is fibrin?

Answer 13

insoluble, cross linked mesh stabilising platelet plug

Question 14

Describe fibrinolysis.

Answer 14

tissue plasminogen activator released from endothelial cells (stimulated by fibrin formation)
cleaves plasminogen to plasmin
plasmin causes fibrin to break down into FDPs

Question 15

What are FDPs?

Answer 15

fibrin degeneration products

Question 16

What are screening tests for secondary haemostasis?

Answer 16

prothrombin time

activated partial thromboplastin time (APTT)

Question 17

What are the consequences of failure of fibrin formation?

Answer 17

pattern of bleeding depends on clotting factors involved and whether its single or multiple abnormalities

Question 18

What are the naturally occurring anticoagulants?

Answer 18

serine protease inhibitors e.g. antithrombin III

protein C and protein S

Question 19

What are thrombophilias?

Answer 19

increased tendency to develop VT

happen when there is a deficiency of naturally occurring anticoagulants

Question 20

Describe the extrinsic and intrinsic pathways of secondary haemostasis.

Answer 20

extrinsic pathway:
TF activates factor VII 
activates factor X and V 
cleaves prothrombin to thrombin 
cleaves fibrinogen to fibrin 

intrinsic pathway:
series of clotting factors activates factor IX and VIII
these help propagate the cascade (amplify activation of X and V)

Question 21

Which important clotting factors are in the extrinsic pathway?

Answer 21

TF (factor II)
V
VII
X

Question 22

Which important factors are in the intrinsic pathway?

Answer 22

IX

VIII