Thrombosis and embolism

Question 1

Define haemostasis

Answer 1

The physiological response of blood vessels to injury. Serves to prevent blood loss through plugging leaks in injured vessels

Question 2

Describe the control of haemostasis

Answer 2

Endothelial cells inhibit haemostasis in healthy vessels and activate heamostasis in injured vessels.

Question 3

How do endothelial cells inhibit haemostasis

Answer 3

Physical insulation of tissues from blood
Producing NO and prostacyclin- both inhibit platelet aggregation.
Express antithrombin on their surface which inactivates thrombin a coagulation enzyme

Question 4

Describe how endothelial cells promote haemostasis

Answer 4

When tissue is injured endothelial cells produce von Willibrand factor which promotes platelet adhesion to extracellular matrix proteins at site of injury, and tissue factor i.e. thromboplastin which activates the clotting cascade.

Question 5

What activates that clotting cascade and platelets

Answer 5

Exposed extra cellular matrix proteins e.g. collagens

Question 6

What do activated platelets secrete

Answer 6

Thromboxane A2 (stimulates activation of new platelets and increases platelet aggregation).
Vasoactive amines and ADP (vasoconstriction?)

Question 7

What is coagulation

Answer 7

A cascade of proteolytic reactions through which inert circulating zymogens (factor V etc) are sequentially activated.

Question 8

What initiates coagulation

Answer 8

Tissue factor e.g. thromboplastin (derived from damaged tissues and endothelial cells),

Question 9

What is the penultimate step in coagulation

Answer 9

Thrombin activation. Thrombin catalyses the conversion of fibrinogen to fibrin monomers which polymerase into fibrin strands which form the meshwork with platelets to form a haemostatic plug.

Question 10

Describe primary haemostasis

Answer 10

Formation of platelet plug

Question 11

Describe secondary heamostasis

Answer 11

Whereby tissue factor (thromboplastin) activates the clotting cascade and there is resulting fibrin deposition.

Question 12

Define thrombosis and thrombus

Answer 12

When the physiological mechanisms of haemostasis are activated inappropriately.
A thrombus is a mass formed from blood constituents within circulation during life

Question 13

What are thrombi composed of

Answer 13

Fibrin, platelets, red and white blood cells

Question 14

What is a thrombus called once it breaks off (or part of it breaks off) and enters the circulation

Answer 14

An embolus

Question 15

What a the three main predisposing factors for thrombosis and what are they called collectively

Answer 15

Changes in vessel wall, changes in blood flow, changes in the constituents of blood.
Virchows triangle

Question 16

Describe changes in the vessel wall including initiators

Answer 16

Occur due to endothelial injury or activation. Initiated by several factors e.g. myocardial infarction, atherosclerotic plaque, vasculitis

Question 17

Describe changes in blood flow consequences and initiators

Answer 17

Damage and activation of endothelial cells due to increased turbulence (hypertension) or stasis (right side heart failure, long flight).

Question 18

Describe initiators to changing blood constituents that increase thrombus

Answer 18

Tissue damage (trauma), post operative, malignancy, cigarette smoke, elevated blood lipids, the pill.

Question 19

Five fates of thrombi

Answer 19

Dissolution
Propogation
Stenosis
Organisation
Embolisation

Question 20

Define an embolus

Answer 20

An intravascular mass that is carried from its site of origin to a distant site within the blood flow

Question 21

Six types of emboli

Answer 21

Thrombus, fat, air, atheromatous debris, bone marrow and amniotic fluid