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ESA2 - Mechanisms Of Disease > Haemostasis, Thrombosis And Embolism > Flashcards

Haemostasis, Thrombosis And Embolism Flashcards

1
Q

What is haemostasis?

A

Stopping of the flow of blood

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2
Q

What factors contribute to successful haemostasis? (5)

A
  • 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)
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3
Q

Explain the role of platelets in haemostasis

A
  • 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)
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4
Q

Name 3 thrombin inhibitors involved in the fibrinolytic cascade

A
  • Antithrombin III
  • Protein C
  • α1 antitrypsin
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5
Q

What factors are released by endothelium during haemostasis and what are their effects?

A
  • Anti-thrombotic factors which PREVENT HAEMOSTASIS

- e.g. t-PA/plasminogen activators, prostacyclin, NO, thrombomodulin

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6
Q

Define thrombosis

A

The formation of a solid mass of blood within the circulatory system of living tissue

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7
Q

What is Virchow’s triad?

A
  • 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)
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8
Q

What is the relevance of Virchow’s triad?

A

Factors that predispose thrombosis

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9
Q

Describe the appearance of an arterial thrombus

A
  • Pale
  • Granular
  • Lines of Zahn
  • Low cell content, more fibrin
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10
Q

Describe the appearance of a venous thrombus

A
  • Deep red
  • Soft and gelatinous
  • Higher cell content, less fibrin
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11
Q

What is the difference in the cause of arterial and venous thrombi?

A

Arterial thrombi are commonly caused by turbulence, whereas venous thrombi are commonly caused by stagnation in blood flow

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12
Q

What are the outcomes of thrombosis?

A
  • 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)
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13
Q

What are the consequences of thrombosis?

A
  • 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)
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14
Q

What is an embolism?

A
  • Blockage of a blood vessel by a solid, liquid or gas at a site distant from its origin
  • 90% of emboli are thromboemboli
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15
Q

Give 3 sites where an thromboemboli may originate from

A
  • Deep vein in leg (DVT)
  • Atheromatous arteries e.g. coronary, carotid, abdominal aorta
  • Chambers of heart (due to turbulent flow caused by arrhythmias)
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16
Q

What are the predisposing factors for DVT? (7)

A
  • Immobility/bed rest
  • Post-op
  • Pregnancy and post partum
  • Oral contraceptives
  • Cardiac failure
  • Disseminated cancer
  • Severe burns
17
Q

Describe the route of a pulmonary embolism that is formed in the popliteal vein

A

Popliteal vein -> Femoral vein -> External iliac vein -> Common iliac vein -> IVC -> Pulmonary artery

18
Q

What methods of prophylaxis may be given to hospital patients who have a high risk of DVT?

A
  • Subcutaneous heparin
  • Leg compression during surgery
  • TED stockings on wards during bed rest
19
Q

How can DVT be treated?

A
  • Intravenous heparin

- Oral warfarin

20
Q

What is the mechanism of action of heparin?

A
  • Anti-thrombin III agonist

- Activates thrombin inhibitors so prevents coagulation cascade

21
Q

What is the mechanism of action of warfarin?

A
  • Vitamin K antagonist
  • Prevents carboxylation of Gla residues, required for the formation of clotting factors II, VII, IX and X so prevents coagulation cascade
22
Q

What is the consequence of repetitive pulmonary embolisms?

A
  • Pulmonary hypertension

- May result in right sided heart failure

23
Q

Describe the effects of a minor, major and massive pulmonary embolism

A
  • 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

ESA2 - Mechanisms Of Disease (8 decks)

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