5. Haemostasis, Thrombosis and Embolism Flashcards
What does successful haemostasis rely on?
Vessel wall, platelets, coagulative system and fibrinolytic system.
What is the role of blood vessles in haemostasis?
Constrict ot limit blood loss.
What are the roles of platelets in haemostasis?
Adhere to damaged vessel wall and each other to form a platelet plug. Also platelet release reaction.
What is the platelet release reaction?
ATP -> ADP. ADP causes platelet aggregation. 5HT and platelet factor 3 are also released, PF3 is important in coagulation.
What type of reaction is coagulation?
A cascade of reactions where a series of inactive components are converted to active components.
What are the key conversions in the coagulation cascade?
Prothrombin to thrombin. Thrombin causes fibrinogen to convert to fibrin.
What are some thrombin inhibitors?
Anti-thrombin III, alpha 1 anti-trypsin, alpha 2 macroglobulin, protein C and S.
What could an inherited deficiency of protein C and S lead to?
Thrombosis.
What is fibrinolysis?
Breakdown of fibrin.
How is the endothelium anti-thrombotic?
Plasminogen activators, prostacyclin, nitric oxide and thrombomodulin.
What is thrombosis?
The formation of a solid mass of blood within the circulatory system during life.
Why does thrombosis occur?
Abnormalities of the vessel wall: atheroma, direct injury or inflammation.
Abnormalities of blood flow: stagnation or turbulence.
Abnormalities of blood components: smokers, post-partum, post-op.
What is the appearance of arterial thrombi?
Pale, granular, lines of Zahn, and lower cell content.
How does the amount of blood cells and fibrin in a thrombi change the colour?
More blood cells makes it more red/brown, more fibrin makes it more yellow.
What is the appearance of venous thrombi?
Soft, gelatinous, deep red and higher cell content.
What are the outcomes of thrombosis?
Lysis, propagation, organisation, recanalisation, or embolism.
What happens in lysis of thrombi?
There is complete dissolution of the thrombus. The fibrinolytic system is active and bloodflow is restored. This is most likely when thrombi are small.
What happens in propagation of thrombi?
There is progressive spread of thrombosis. Distally in arteries and proximally in veins, the thrombus gets bigger in the direction of flow of blood.
What happens in organisation of thrombi?
It is a reparative process with ingrowth of fibroblasts and capillaries. The lumen remains obstructed.
What happens in recanalisation of thrombi?
Bloodflow is re-established but usually incompletely. One of more channels formed through organising thrombus.
What happens in embolism of thrombi?
Parts of the thrombus breaks off and travels through the bloodstream until it lodges at a distant site.
What are the effects of arterial thrombosis?
Ischaemia or infarction - depends on site and collateral circulation.
What are the effects of venous thrombosis?
Congestion, oedema, ischaemia and infarction (more unlikely if venous).
What is an embolism?
The blockage of a blood vessel by solid, liquid or gas at a site distant from its origin.
What is the most common type of embolism?
Thrombo-embolism, 90% of emboli.
What causes air embolism commonly?
Slitting the throat as the air and residual blood mixes to form a froth that is difficult to circulate and causes an embolism.
When can amniotic fluid by a cause of embolism?
Mostly with illegal abortions but can still happen in childbirth today or miscarriages.
Where will the following thrombo-emboli end up?
a. from systemic veins
b. from the heart
c. from atheromatous carotid arteries
d. from atheromatous abdominal aorta
a. to the lungs, pulmonary embolism.
b. via the aorta to renal, mesenteric, and other arteries.
c. pass to the brain, causes a stroke.
d. to arteries of the legs.
What are the predisposing factors of deep vein thrombosis?
Immobility or bed rest, post-operative, pregnancy and post-partum, oral contraceptive especially in the past, sever burns, cardiac failure, and disseminated cancer.
How can DVT be prevented?
High risk patients identified and offered prophylaxis: heparin sub-cutaneously, or leg compression during surgery.
How can DVT be treated?
Using intravenous heparin or oral warfarin.
Wat are the effects of the different classes of pulmonary embolism?
Massive PE: >60% reduction in bloodflow and is rapidly fatal.
Major PE: medium sized vessels blocked, short of breath and coughing up blood stained sputum.
Minor PE: small peripheral pulmonary arteries blocked, asymptomatic or minor shortness of breath.
What does recurrent minor pulmonary embolism lead to?
Pulmonary hypertension.
