Session 5-Haemostasis

Question 1

Define haemostasis

Answer 1

Stoppage of bleeding or haemmorhage, either by normal vasoconstriction, abnormal obstruction or coagulation

Question 2

What produces platelets in the bone marrow?

Answer 2

Megakaryocytes

Question 3

What is the normal life span of platelets?

Answer 3

7-10 days

Question 4

What are the principles of haemostasis? (3)

Answer 4

1) prevent bleeding
2) prevent unnecessary coagulation, allow blood to flow
3) make clot, control clotting and break it down

Question 5

What is the normal platelet count?

Answer 5

150-400 x 10^9/L

Question 6

When does platelet adhesion occur?

Answer 6

When there is damage to a vessel wall and underlying tissues are exposed

Question 7

What do platelets adhere to and via which receptor do they do this?

Answer 7

Adhere to collagen via vWF (Von Willebrand factor) receptor

Question 8

What activates platelets?

Answer 8

Secretion of ADP, thromboxane and other substances

Question 9

How does platelet activation provide some coagulation factors?

Answer 9

By secretion from internal stores

Question 10

What is platelet aggregation?

Answer 10

Cross linking of platelets to form platelet plug

Question 11

What are some mediating factors of haemostasis?

Answer 11

1) Plt receptors - glycoprotein complexes
2) Von willebrands factor
3) fibrinogen
4) collagen
5) ADP
6) thromboxane/arachidonic acid
7) thrombin

Question 12

What is the clotting cascade?

Answer 12

Amplification system activation of precursor proteins to generate thrombin

Question 13

What does thrombin convert?

Answer 13

Soluble fibrinogen into insoluble fibrin

Question 14

How is the clotting cascade controlled?

Answer 14

1) natural anticoagulants to inhibit activation

2) clot destroying proteins which are activated by clotting cascade

Question 15

Give examples of coagulation factors

Answer 15

Fibrinogen
Prothrombin
Factors 5, 7, 8, 9, 10, 11, 13
Tissue factor

Question 16

Give examples of natural anticoagulants

Answer 16

Protein C and S
Antithrombin
Tissue factor pathway inhibitor

Question 17

What activates the extrinsic pathway?

Answer 17

Factor VII

Question 18

What activates the intrinsic pathway?

Answer 18

Factors VIII, IX, XI, XII

Question 19

Describe the clot forming process (6)

Answer 19

1) tissue factor exposure
2) initiation produces small amount of thrombin
3) thrombin feeds back and activates other clotting factors
4) produces thrombin burst
5) thrombin cleaves fibrinogen to fibrin
6) clot forms

Question 20

What is the Von willebrand factor?

Answer 20

Involved in platelet adhesion to vessel wall, platelet aggregation and also carries and stabilises factor VIII

Question 21

How is the vessel wall important in haemostasis?

Answer 21

1) vasoconstriction (reduces haemorrhage)
2) production of vWF factor
3) exposure of collagen and tissue factor which initiates activation of clotting factors

Question 22

What is the purpose of fibrinolysis?

Answer 22

Breaks down thrombi to prevent them from remaining in place and growing

Question 23

Where is plasminogen produced?

Answer 23

Liver

Question 24

Which enzyme breaks down fibrin?

Answer 24

Plasmin

Question 25

What is the precursor of plasmin?

Answer 25

Plasminogen

Question 26

Give examples of congenital coagulation factor disorders

Answer 26

``` Haemophilia A (factor 8 deficiency) Haemophilia B (factor 9 deficiency) ```

Question 27

What is vitamin K needed for?

Answer 27

Metabolism of factors 2, 7, 9 and 10

Question 28

What complications can coagulation factor disorders cause?

Answer 28

1) muscle haematomas 2) recurrent haemarthroses (bleeding into joints) 3) joint pain and deformity 4) prolonged bleeding post dental extraction 5) life threatening post op bleeding 6) intracerebral haemorrhage

Question 29

True or false: haemophilia A is an X linked recessive condition

Answer 29

TRUE

Question 30

How is haemophilia A treated?

Answer 30

Recombinant factor VIII

Question 31

True or false: Von willebrand disease is autosomal dominant

Answer 31

TRUE

Question 32

What does Von willebrand's disease lead to?

Answer 32

1) Abnormal platelet adhesion to vessel wall | 2) Reduced factor VIII amount/activity

Question 33

What can vessel wall abnormalities lead to?

Answer 33

Easy bruising | Spontaneous bleeding from small vessels in skin and sometimes mucous membranes

Question 34

What can a low platelet count be due to?

Answer 34

1) Reduced production | 2) Increased removal (non-immune destruction, immune destruction, splenic pooling)

Question 35

What causes the immune destruction of platelets?

Answer 35

Immune thrombocytopenic purpura- autoantibodies against glycoproteins

Question 36

How is immune thrombocytopenic purpura treated?

Answer 36

With immunosuppression

Question 37

What can lead to reduced production of platelets?

Answer 37

1) B12/folate deficiency 2) Infiltration of bone marrow by cancer cells or fibrosis 3) Drugs - chemo, antibiotics 4) Viruses - HIV, hepatitis

Question 38

True or false: patients with severe thrombocytopenia are always symptomatic

Answer 38

FALSE - generally not symptomatic until platelet count is less than 30

Question 39

What are the consequences of severe thrombocytopenia?

Answer 39

1) Easy bruising 2) Petechiae and purpura 3) Mucosal bleeding 4) Severe bleeding after trauma 5) Intracranial haemorrhage

Question 40

What is the difference between petechiae and purpura?

Answer 40

``` Petechiae = small red spots of bleeding in skin Purpura = rash of purple spots-internal bleeding of small vessels ```

Question 41

What is the main way in which platelet function disorders can be acquired?

Answer 41

Aspirin/NSAIDS/clopidogrel

Question 42

What is disseminated intravascular coagulopathy (DIC)?

Answer 42

Microthrombi form in circulation, leading to consumption of clotting factors and platelets and haemolytic anaemia

Question 43

What type of anaemia is disseminated intravascular coagulopathy?

Answer 43

Microangiopathic haemolytic anaemia

Question 44

What are the triggers of disseminated intravascular coagulopathy?

Answer 44

1) malignancy 2) massive tissue injury eg burns 3) infections (gram negative sepsis) 4) massive haemorrhage and transfusion 5) ABO transfusion reaction 6) obstetric causes