Haemostasis

Question 1

What does haemostasis do? [3 marks]

Answer 1

• Prevents tissue loss from tissue injury
• Restores vascular integrity & promotes healing
• Limits infection

Question 2

What are the four key components of haemostasis? [4 marks]

Answer 2

• Endothelium
• Coagulation
• Platelets
• Fibrinolysis

Question 3

How does the horseshoe crab maintain haemostasis? [2 marks]

Answer 3

• A primitive coagulation pathway is initiated for endotoxin.
• Its haemolymph contains amoebocytes which wards off infection by bordering up the infected area.

Question 4

What are the stages of haemostasis? [6 marks]

Answer 4

• Vascular spams
• Platelet activation
• Haemostatic plug
• Coagulation
• Stable clot formation
• Clot dissolution

Question 5

What makes up a blood clot? [3 marks]

Answer 5

• Fibrin mesh
• Platelets
• Erythrocytes

Question 6

What does the vessel wall do? [3 marks]

Answer 6

• Inhibits coagulation
• Prevents platelet aggregation
• Provides a barrier to reactive element in the subendothelium such as collagen and TF

Question 7

What happens in primary haemolysis? [3 marks]

Answer 7

• Vasoconstriction (immediate)
• Platelet adhesion (within seconds)
• Platelet aggregation and contraction (within minutes)

Question 8

What happens in secondary haemolysis? [2 marks]

Answer 8

• Activation of coagulation factors tissue factor and collagen (within seconds)
• Formation of fibrin (within minutes)

Question 9

What happens of fibrinolysis? [2 marks]

Answer 9

• Activation of fibrinolysis (within minutes)

- Lysis of the plug (within hours)

Question 10

What forms does von Willebrand factor come in? [2 marks]

Answer 10

• Globular in the subendothelium

- Filamentous in blood (unravels)

Question 11

How is vWF distributed? [2 marks]

Answer 11

• 95% in the constitutive path: leaves cell via vesicles in Golgi apparatus
• 5% in the regulated path: via Weibel-Palade bodies

Question 12

What does thrombin do? [2 marks]

Answer 12

• Activates circulating platelets

- These platelets release more clotting factors.

Question 13

Where does secondary haemostasis occur? [1 mark]

Answer 13

Negatively-charged phospholipid membrane from activated platelets

Question 14

How do platelets stick to vWF? [1 mark]

Answer 14

Via glycoproteins on vWF

Question 15

What does vWF do? [2 marks]

Answer 15

• Forms a bridge between collagen and platelets

- Protects FVIII from rapid clearance

Question 16

Where are most clotting factors made? [1 mark]

Answer 16

In the liver

Question 17

What does the extrinsic clotting factor involve? [3 marks]

Answer 17

• FVIIa-X complex formed
• FVa activates prothrombin
• Fibrogen comes out of solution to become X linked fibrin mesh

Question 18

What does the intrinsic clotting factor involve? [1 mark]

Answer 18

Prekalikrein

Question 19

What happens at the initiation of clot formation? [3 marks]

Answer 19

• Exposed tissue factor binds to FVIIa
• Complex binds small bits of FX and FV
• Small amount of thrombin produced

Question 20

What happens at the propagation of clot formation? [2 marks]

Answer 20

• Activated factors enable binding of FXa and FVa to surface membranes
• Exposes the reaction sites necessary
• Thrombin burst allows large scale production of fibrin

Question 21

What converts plasminogen to plasmin? [1 mark]

Answer 21

Tissue plasminogen activator

Question 22

What are formed when cross-linked fibrin is degraded? [1 mark]

Answer 22

D dimers

Question 23

What are formed when non-cross-linked fibrin is degraded? [1 mark]

Answer 23

Fibrin degradation products

Question 24

What can tissue plasminogen activator (tPA) be used for? [2 marks]

Answer 24

• Therapeutic thrombolysis

- Alongside streptokinase (bacterial activator)

Question 25

What causes ecchymosis (easy bruising)? [2 marks]

Answer 25

High levels of:

• fibrinolytic factors
• anticoagulant proteins

Question 26

What causes chronic venous insufficiency (clotting)? [2 marks]

Answer 26

High levels of:

• coagulation factors
• platelets