Haemostasis

Question 1

What is haemostasis?

Answer 1

Preventing or stopping bleeding in cases of trauma or disease whilst maintaining blood in its fluid state

Question 2

What are the three major steps of haemostasis?

Answer 2

1. Vasoconstriction
2. Platelet plug
3. Blood coagulation/ fibrin clot formation

Question 3

What is the aim of haemostasis?

Answer 3

To seal the hole until tissues are repaired in order to prevent excessive bleeding

Question 4

What happens to the clot once the vessel integrity is restored?

Answer 4

Fibrinolysis (clot is broken down)

Question 5

What is the role of platelets in clot formation?

How are they activated?

Answer 5

Platelets adhere to collagen via von Willebrands Factor and interlink to form a “platelet plug” - primary haemostasis

Question 6

What do platelets do once they are activated?

Answer 6

They secrete ATP and Thromboxane and other activators of the clotting cascade

Question 7

What is the difference between the “intrinsic” and “extrinsic” pathways of the coagulation cascade?
What factors are involved in each?

Answer 7

Intrinsic pathway is activated by damage to surfaces and extrinsic pathway is activated by trauma (endothelial cell injury)
Intrinsic: XII, XI, IX, VIII
Extrinsic: VII

Question 8

Name some natural anticoagulants that are necessary to prevent further coagulation once the vessel integrity is resolved

Answer 8

Protein C
Protein S
Anti-thrombin

Question 9

What is the common pathway of coagulation that occurs despite “intrinsic” or “extrinsic” activation?

Answer 9

Prothrombin —> Thrombin (Thrombin burst)

Soluble fibrinogen—> Insoluble FIBRIN which cross links to form the clot

Question 10

Factor VIII is carried by and protected by what?

Answer 10

von Willebrands Factor (vWF)

Question 11

How can we measure coagulation clinically?

Answer 11

Extrinsic:
INR
PT (Prothrombin time)

Intrinsic:
aPTT (activated partial thromboplastin time)

Question 12

Name two congential coagulation factor disorders

Answer 12

Haemophilia A  (Factor VIII)
Haemophilia B (Factor IX)

Question 13

Name some ways that coagulation factor disorders may be acquired

Answer 13

Liver disease
Vitamin K deficiency
Anticoagulant medication

Question 14

How might coagulatoin factor disorders present?

Answer 14

Muscle haematomas
Recurrent bleeding into joints
Prolonged bleeding
Joint pain

Question 15

What is von Willebrand’s Disease?

How does it present clinically?

Answer 15

Reduced production or activation of vWF which leads to abnormal platelet adhesion to vessel walls and reduced Factor VIII activity
Skin and mucous membrane bleeding and prolonged bleeding after trauma

Question 16

Name two congenital vessel wall abnormalities

Answer 16

Hereditary Haemorrhagic Telangiectasia (HHT)

EDS

Question 17

Name some ways in which vessel wall abnormalities can be acquired

Answer 17

Senile purpura
Steroids
Infection
Scurvy

Question 18

What is low platelet count known as?

Answer 18

Thrombocytopenia

Question 19

In what ways can platelet levels be lowered?

Answer 19

Immune destruction: ITP, autoimmune disease
Non-immune destruction: DIC, TTP, HUS
Reduced production: B12/folate deficiency, cancer cell nfiltration, drugs (chemo.), viruses

Question 20

What disorders of platelet function “qualitative” are there?

Answer 20

Bernard Soulier (very rare)
Drugs: aspirin, NSAIDs
Myeloproliferative disorders
Myeloma