Haemostasis, Thrombosis And Embolism Flashcards
What is haemostasis?
Stopping of the flow of blood
What factors contribute to successful haemostasis? (5)
- Contraction of vessel wall to limit blood loss
- Adhesion of platelets, formation of a platelet plug and activation of platelet release reaction
- Coagulation cascade (formation of fibrin mesh; requires thrombin)
- Fibrinolytic cascade (thrombin inhibitors and plasmin activation)
- Endothelium factors (prostacyclin, NO, anti-thrombotic factors all limit haemostasis)
Explain the role of platelets in haemostasis
- Adhere to damaged vessel wall forming a platelet plug
- Release of thromboxane A2 and ADP -> vasoconstriction
- Platelet release reaction (release of 5HT and platelet factor 3 which activate coagulation cascade)
Name 3 thrombin inhibitors involved in the fibrinolytic cascade
- Antithrombin III
- Protein C
- α1 antitrypsin
What factors are released by endothelium during haemostasis and what are their effects?
- Anti-thrombotic factors which PREVENT HAEMOSTASIS
- e.g. t-PA/plasminogen activators, prostacyclin, NO, thrombomodulin
Define thrombosis
The formation of a solid mass of blood within the circulatory system of living tissue
What is Virchow’s triad?
- Abnormalities of blood flow (e.g. Turbulence, stagnation)
- Abnormalities of the vessel wall (e.g. Atheroma, inflammation)
- Abnormalities of blood constituents (e.g. SMOKING, post op, post partum)
What is the relevance of Virchow’s triad?
Factors that predispose thrombosis
Describe the appearance of an arterial thrombus
- Pale
- Granular
- Lines of Zahn
- Low cell content, more fibrin
Describe the appearance of a venous thrombus
- Deep red
- Soft and gelatinous
- Higher cell content, less fibrin
What is the difference in the cause of arterial and venous thrombi?
Arterial thrombi are commonly caused by turbulence, whereas venous thrombi are commonly caused by stagnation in blood flow
What are the outcomes of thrombosis?
- Lysis (complete dissolution)
- Propagation (progressive spread)
- Organisation (ingrowth of granulation tissue)
- Recanalisation (small channels formed through thrombus)
- Embolism (part breaks off and lodges at a distant site)
What are the consequences of thrombosis?
- Arterial - Ischaemia and infarction of organs due to narrowing/occlusion of vessels supplying tissues
- Venous - congestion and oedema as venous return to the heart is impaired (may indirectly cause ischaemia)
What is an embolism?
- Blockage of a blood vessel by a solid, liquid or gas at a site distant from its origin
- 90% of emboli are thromboemboli
Give 3 sites where an thromboemboli may originate from
- Deep vein in leg (DVT)
- Atheromatous arteries e.g. coronary, carotid, abdominal aorta
- Chambers of heart (due to turbulent flow caused by arrhythmias)
What are the predisposing factors for DVT? (7)
- Immobility/bed rest
- Post-op
- Pregnancy and post partum
- Oral contraceptives
- Cardiac failure
- Disseminated cancer
- Severe burns
Describe the route of a pulmonary embolism that is formed in the popliteal vein
Popliteal vein -> Femoral vein -> External iliac vein -> Common iliac vein -> IVC -> Pulmonary artery
What methods of prophylaxis may be given to hospital patients who have a high risk of DVT?
- Subcutaneous heparin
- Leg compression during surgery
- TED stockings on wards during bed rest
How can DVT be treated?
- Intravenous heparin
- Oral warfarin
What is the mechanism of action of heparin?
- Anti-thrombin III agonist
- Activates thrombin inhibitors so prevents coagulation cascade
What is the mechanism of action of warfarin?
- Vitamin K antagonist
- Prevents carboxylation of Gla residues, required for the formation of clotting factors II, VII, IX and X so prevents coagulation cascade
What is the consequence of repetitive pulmonary embolisms?
- Pulmonary hypertension
- May result in right sided heart failure
Describe the effects of a minor, major and massive pulmonary embolism
- Minor - occludes a small pulmonary artery, usually asymptomatic or may have SOB
- Major - occludes a medium pulmonary artery, may have SOB and/or coughing of blood stained sputum
- Massive - >60% reduction in blood flow, may lead to hypoxia -> multi organ failure
