Haemostasis

Question 1

What is haemostasis

Answer 1

The arrest of bleeding &
the maintenance of vascular patency

Question 2

What are the 4 requirements of haemostasis

Answer 2

• Permanent state of readiness
• Prompt response
• Localised response
• Protection against unwanted thrombosis

Question 3

State the 4 components of a normal haemostatic system

Answer 3

• Primary haemostasis (platelet plug formation)
• Secondary haemostasis (fibrin clot formation)
• Fibrinolysis (fibrin clot break down)
• Anti-coagulant defences

Question 4

Describe the formation of a platelet and state where this occurs

Answer 4

Formed by ‘budding’ from megakaryocytes
Occurs in the bone marrow

Question 5

Describe the structure of a platelet

Answer 5

• Small anucleated discs
• Composed of phospholipids
• Store & release calcium & other chemicals
• ~7-10 day life span
  (aspirin should be stopped a week before surgery)

Question 6

Describe the stages of primary haemostasis

Answer 6

Endothelial damage ⇒
Collagen exposure ⇒
Von Willebrand factor release ⇒
Platelet adhesion ⇒
Chemical signal release ⇒
Aggregation of platelets at site

Question 7

Thinking about the stages of primary haemostasis, state the three main causes of failure to form a platelet plug

Answer 7

Vascular problem (low levels of collagen/weak wall)
Von willebrand factor problem (low levels of VWF)
Platelet problem (low levels or function of platelets)

Question 8

Clinical presentation (/consequences) of failure to form a platelet plug

Answer 8

• Spontaneous bruising
• Non-blanching purpuric rash
• Mucosal bleeding (epistaxes, GI, conjunctival, mennorhagia)
• Intracranial haemorrhage
• Retinal haemorrhage

Question 9

Primary haemostasis screening test

Answer 9

• Platelet count

Question 10

What is the name for low platelet count

Answer 10

Thrombocytopenia

Question 11

Describe the stages of secondary haemostasis

Answer 11

• Clotting activators attach to platelet phospholipids
• TF/VIIa (extrinsic) & VIII/IXa (intrinsic) → Activates V/Xa
• V/Xa stimulates prothrombin → thrombin conversion
• Thrombin stimulates fibrinogen → fibrin conversion & causes VIII/IXa amplification (positive feedback)

Question 12

Thinking about the stages of secondary haemostasis, state the three main causes of failure to form a fibrin clot

Answer 12

• Single clotting factor deficiency (usually hereditary)
  (e.g. Haemophillia)
• Multiple clotting factor deficiency (usually acquired)
  (e.g. DIC)
• Increased fibrinolysis (usually complex coagulopathy)

Question 13

Describe the stages of fribinolysis

Answer 13

Tissue Plasminogen Activator (tPA) converts Plasminogen to Plasmin ⇒
Plasmin converts Fibrin to Fibrin Degradation Products (FDP)

Question 14

Where do patients with haemophilia A tend to bleed into

Answer 14

Load bearing joints e.g. knee, ankle, elbow

Question 15

State the 2 screening tests for secondary haemostasis and state which pathway they measure

Answer 15

Prothrombin time
- measures extrinsic pathway & common clotting pathway

(Activated) partial thromboplastin time (APTT)
- measures intrinsic pathway & common clotting pathway

Question 16

State the two main naturally occurring anticoagulants and state their effect

Answer 16

Anti thrombin
- It switches off thrombin
(& deactivates factor TF/VIIa, VII/IXa, V/Xa)

Protein C & (cofactor) Protein S
- It deactivates factors VIII/IXa and V/Xa (extrinsic & common)

Question 17

What type of anticoagulant is anti-thrombin

Answer 17

It is a serine protease inhibitor

Question 18

What is the name of the complex that activates protein C

Answer 18

Thrombin-thrombomodulin complex

Question 19

What is thrombophilia a deficiency of?

Answer 19

Naturally occurring anticoagulants

Question 20

What do patients with thrombophilia have an increased tendency to do?

Answer 20

Develop venous thrombosis (DVT/PE)