Haemostasis

Question 1

What is haemostasis?

Answer 1

Cessation of bleeding whilst maintaining vascular patency

Question 2

Define primary haemostasis

Answer 2

Formation of platelet plug

Question 3

Define secondary haemostasis

Answer 3

Formation of fibrin clot

Question 4

List components of normal haemostatic system

Answer 4

Primary haemostasis
Secondary haemostasis
Fibrinolysis
Anticoagulation

Question 5

How are platelets formed?

Answer 5

Formed in bone marrow by budding from megakaryocytes

Question 6

Describe the appearance of platelets on blood film

Answer 6

Small anucleate discs

Question 7

List, in order, the stages of platelet plug formation

Answer 7

Endothelial DAMAGE exposes collagen
Release of vWF + proteins with platelets receptors
Platelet ADHESION at site of injury
SECRETION of proteins that attract more platelets
Platelet AGGREGATION at site of injury

Question 8

List causes of failure of platelet plug formation

Answer 8

Vascular
Less platelets (thrombocytopaenia)
Reduced platelet function
Von Willebrand factor deficiency

Question 9

List consequences of failure of platelet plug formation

Answer 9

Spontaneous bruising and purpura
Mucosal bleeding (epistaxis, GI, conjunctival, menorrhagia)
Intracranial haemorrhage
Retinal haemorrhage

Question 10

What is purpura?

Answer 10

Non-blanching red or purple discolored spots on the skin, typically of the lower limbs

Question 11

What is the main screening test/investigation for primary haemostasis?

Answer 11

Platelet count

Question 12

List, in order, the stages of fibrin clot formation

Answer 12

INITIATION: TF/VIIa activate V/XA
V/Xa facilitate the formation of prothrombin (II)
Prothrombin is converted into thrombin (IIa)
Thrombin activates fibrinogen (I)
PROPAGATION: Fibrinogen is converted into fibrin (IIa)
AMPLIFICATION: Thrombin activates VIII/IXa which produces more V/Xa and more thrombin

Question 13

List causes of failure of fibrin clot formation and give examples

Answer 13

Single clotting factor deficiency usually heridatory e.g. haemophilia 
Multiple clotting factor deficiencies usually acquired e.g. DIC, liver failure
Increased fibrinolysis (part of complex coagulopathy)

Question 14

Outline a clinical approach to bleeding disorders

Answer 14

History (bleeding/bruising, duration)
PMHx (surgery, dental extractions)
DHx
FHx
Examination

Question 15

List consequences of failure of fibrin clot formation

Answer 15

No characteristic clinical syndrome, can be both primary or secondary haemostatic failure

Question 16

What is thrombophilia?

Answer 16

Deficiency of naturally occuring anticoagulants, usually heridatory, leading to an increased tendancy to develop venous thrombosis (DVT/ PE)

Question 17

Protein C is converted to an anticoagulant serine protease by a complex between _____ and ______

Answer 17

Thrombin

Thrombomodulin

Question 18

What is Von Willebrand Factor?

Answer 18

Acts as a glue to help platelets stick to each other and to the endothelial wall

Question 19

What clotting factor does vWF carry?

Answer 19

Factor VIII

Question 20

What is the lifespan of a platelet?

Answer 20

7-10 days

Question 21

Following endothelial vessel wall damage, collagen is exposed and releases which factor to attract platelets to adhere?

Answer 21

Von Willebrand Factor

Question 22

Why is platelet plug formation impaired in older people, causing easy bruising?

Answer 22

Lose collagen from vessel wall with age - less Von Willebrand Factor and thus less platelet adherance and aggregation

Question 23

Which factor is released from damaged vascular endothelium during fibrin clot formation? Which factor does it activate?

Answer 23

Tissue factor

activates factor VIIa

Question 24

Which factors are activated by factor VIIa, VIII and IXa in fibrin clot formation?

Answer 24

V

Xa

Question 25

What is the effect of factors V and Xa in the propagation step of fibrin clot formation?

Answer 25

Encourage formation of thrombin from prothrombin

Question 26

What is the effect of thrombin in fibrin clot formation?

Answer 26

Encourages formation of fibrin from fibrinogen

Question 27

Describe the fibrinolytic pathway (breakdown of a clot)

Answer 27

Tissue plasminogen factor causes plasmin formation from plasminogen
Plasmin causes breakdown of fibrin to fibrin degradation products (D-dimers)

Question 28

What are the main screening tests/investigations for secondary haemostasis?

Answer 28

Prothrombin time (PT time)
Activated partial thromboplastin time (APTT)