Thrombosis and Embolism

Question 1

Define thrombosis.

Answer 1

• Intravascular coagulation of blood
• Causes interruption of blood flow

Question 2

What are the three main elements of Virchow’s Triad?

Answer 2

• Endothelial Injury (causing platelet adhesion/aggregation)
• Hypercoagulability
• Alteration in normal blood flow

Question 3

What factors naturally inhibit thrombosis?

Answer 3

• Vasodilators and platelet inhibitors by endothelial cells
• EXAMPLES: NO (antiplatelet effect), Antithrombin (anticoagulant effect), plasminogen activator (fibrinolytic effect)

Question 4

What factors provoke thrombosis?

Answer 4

• Release of vasoconstrictors and platelet activators by endothelial cells
• EXAMPLE: Endothelins and von Willebrand factors. ACTIVATE THROMBOXIN A WHICH STIMULATES PLATELETS
• Tissue factor (procagulant effects) and inhibitors of plasminogen activator (antifibrinolytic effects)

Question 5

Describe pale thrombus and red thrombus.

Answer 5

• PALE THROMBUS - Platelets adhere to endothelium and become activated. Coagulation generates fibrin
• RED THROMBUS - Lumen occluded by thrombus, causing RBCs to adhere to surface

Question 6

§

What is thrombus propagation?

Answer 6

• Where occlusion of the main vein causes red thrombus in front and behind

Question 7

Why are systemic venous thrombosis common?

Answer 7

• Slow blood flow, lower pressure
• Consists of red cells, platelets and fibrin ( RED thrombus)

Question 8

Describe arterial thrombus.

Answer 8

• Common in arteries due to atheroma
• Thrombus consists mainly of platelets (WHITE thrombus)

Question 9

The main effects of alterations in blood flow is to bring platelets into contact with the vessel wall. What causes this and what happens?

Answer 9

• CAUSES: Slowing of blood flow e.g during cardiac failure
• During slowing, normal axial stream of blood cells lost. White cells and platelets fall out of main stream and accumulate in plasma zone.

Question 10

What two conditions are associated with alterations in blood flow?

Answer 10

• STASIS (Immobility) - Involved in venous thrombosis
• TURBULENCE (Disturbed movement) - Involved in arterial fibrillation

Question 11

Why does a change in blood flow cause thrombosis?

Answer 11

• Brings platelets into contact with endothelium
• Promotes endothelial injury and increased procoagulant activity
• Prevents dilution of activated clotting factors
• Prevents flowing in of inhibitors of clotting factors

Question 12

What may cause a change in blood composition?

Answer 12

• INCREASE IN platelets, fibrinogen and prothrombin following operations
• INCREASE in platelet adhesiveness following surgery
• Abnormalities of thrombosis inhibitors
• Miscellaneous factors e.g cancer, smoking

Question 13

What are the different fates of thrombus?

Answer 13

• Dissolution
• Propagation
• Embolisation

Question 14

What are embolisms and what can cause them?

Answer 14

• Passage and trapping of object in vasculature
• Can be caused by atherosclerosis

Question 15

Describe when fat embolism commonly occurs.

Answer 15

• Following massive trauma, bone marrow transplant, liposuction and patients with pancreatitis

Question 16

When can air embolisms occur?

Answer 16

• Entry of atmospheric air into blood when neck or intracranial veins are incised
• During great ascents, gas bubbles form and obstruct blood flow

Question 17

What are infarctions?

Answer 17

• Necrosis results from ischaemia caused by obstruction of blood supply
• Caused by embolisms

Question 18

What are white/pale infarcts?

Answer 18

• Have arterial occlusions
• Occur in solid organs
• With end-arterial circulation without a dual blood supply
• Tissues with increased density, prevent diffusion of RBCs from capillaries into necrotic area

Question 19

What are red/haemorrhagic infarcts?

Answer 19

• Red cells spread into necrotic area
• Occur in lungs and GI tract
• Tissues are well vascularised with overlapping blood supplies
• Caused by venous occlusions