MoD Haemostasis, thrombosis and embolism

Question 1

Define Haemostasis (not homostasis!) and state the factors needed for successful haemostasis

Answer 1

Haemostasis is stopping bleeding
Needs:
- vessel wall
- platelets
- coagulation system (promotes formation of solid mass)
- fibrinolytic system (opposes coag system to control haemostasis

Question 2

What is the role of each of the following in haemostasis:

• vessels walls
• platelets
• coagulation system
• fibrinolytic system

Answer 2

Vessel walls constrict to limit blood loss

Platelets adhere to the damaged vessel wall and each other, to form a platelet plug

The coagulation system is a coag cascade, prothrombin is converted to thrombin then fibrinogen is converted to fibrin (there are thrombin inhibitors to tightly regulate coagulation)

The fibrinolytic system breaks down fibrin - plasminogen is converted to plasmin which breaks down fibrin

Question 3

Define thrombosis

Answer 3

The formation of a solid mass of blood within the circulatory system during life (inc heart)

Question 4

Why does thrombosis occur?

Answer 4

Abnormalities of the vessel wall such as atheroma, inflammation or trauma
Abnormalities of blood flow such as stagnation and turbulence
Abnormalities of blood components, seen in smokers, post partum (beneficial to prevent haemorrhage when placenta has come away)

Note: Virchow’s triad of factors contributing to thrombosis: endothelial injury, stasis of blood flow, hypercoagulabilty

Question 5

What do thrombi look like?

Answer 5

Arterial thrombi are pale, granular and have lines of Zahn (dark layers have more rbc and light layers have more fibrin)

Question 6

What are the outcomes of thrombosis?

there are 5

Answer 6

Small thrombi can undergo lysis - the fibrinolytic system is activated, and blood flow is re-established

Propagation - the thrombus can get bigger in the direction of blood flow

Organisation - a reparative process where the thrombus is changed histologically. Lumen remains obstructed

Recanalisation - blood flow is only partially restored, channels form through the thrombus

Embolism - part of the thrombus breaks off and lodges at a distant site e.g. pulmonary embolism

Question 7

Define embolism

Answer 7

The blockage of a blood vessels by a solid, liquid or gas at a site distant from its origin

Question 8

What are the types of embolism?

Answer 8

• thrombo-embolism (90%)
• air e.g. cut jugular
• amniotic fluid eg miscarriage
• nitrogen
• medical equipment
• tumour cells
• cholesterol embolism

Question 9

What are the predisposing factors to deep vein thrombosis?

Answer 9

Immobility
Post-operative
Pregnancy and post part
Oral contraceptives
Sever burns
Cardiac failure

Question 10

What are the effects of pulmonary embolism?

Answer 10

Massive PE = reduction in blood flow (fatal)
Major PE = medium vessels blocked, short of breath and bloody sputum
Minor PE = small peripheral arteries blocked, minor shortness of breath
Recurrent minor PEs = pulmonary hypertension