thrombosis and haemostasis

Question 1

what is haemostasis?

Answer 1

• a well regulated process that maintains blood in a** fluid, clot free state** in normal vessels and** induces the rapid formation of a localised haemotstaic plug **at the site of vascular injury

Question 2

what is thrombosis?

Answer 2

• abnormal activation of blood clotting in an uninjured vessel leadinfg to the formation of a blood clot or thrombus within the vascular system, which can obstruct the flow of blood

Question 3

what is a thrombus?

Answer 3

• an aggregate of **coagulated blood **containing **platelets, fibrin and entrapped cellular elements **

Question 4

what are the predisposing factors of thrombus formation?

virchow’s triad

Answer 4

* endothelial injury (inner layer of blood vessel) - injuries can occur due to hsemodynamic stress
* changes in blood flow- eg stasis and turbelent flow can promote thrombus
* changes in **constituents of blood **

Question 5

what is the normal blood flow pattern?

Answer 5

laminar flow - cellular elements flow centrally in the vessel lumen

Question 6

how can a change in endothelial surface lead to thrombus formation?

Answer 6

• injury to the endothelial surface may be due to **hypertension or turbulent flow **
• thrombosis occurs from exposure of the stroma and causes increased platelet adhesion

Question 7

what can happen as a result of turbelent flow of blood?

Answer 7

• disrupted flow brings platelets into contact with the endothelium
• prevents dilution of activated clotting factors by flowing blood

Question 8

what is hypercoagulability & what can cause it?

Answer 8

• alteration of the coagulation pathways - risk for thrombosis
• heritable - protein deficiencies, factor V leiden or acquired through pregnancy, oral contraceptives (due to increase in oestrogen)

Question 9

what is the stasis of blood?

Answer 9

stoppage or slow down in the flow of blood

Question 10

what can cause thrombosis in the venous system?

Answer 10

most commonly due to stasis

Question 11

what is an atheroma?

Answer 11

a fatty material that builds up in your arteries

Question 12

what kind of people are at risk for arterial thrombosis?

Answer 12

• smokers
• people with high cholesterol

Question 13

why does an atheroma not occur in the venous system?

Answer 13

as the blood pressure is lower

Question 14

where in the veins do thrombosis occur?

Answer 14

the valves

Question 15

what are the risk factors for venous thrombosis?

Answer 15

• immobility eg after surgery, deep vein thrombosis could occur
• smoking
• cancer - can cause hypercoagulability
• pregnancy
• oestrogen therapy eg birth control or hrt
• dehydration

Question 16

how does a arterial thrombus present?

Answer 16

• loss of pulse
• pale, cold extremities
• painful
• death and gangrene of the affected limb or site

Question 17

how does a venous thrombus present?

Answer 17

• tender
• swollen
• reddened
• 95% occur in leg veins

Question 18

what can happen ton a thrombus once it is formed?

Answer 18

• lysis and resolution - degradation
• it can become a scar tissue and permanently occlude the vessel
• recanalisation- ingrowth of new vessel which eventually joins up to restore blood flow at least partially
• embolisation - part of the thrombus will dislodge, and then travel to a different site

Question 19

what is an embolism?

Answer 19

• a detached intravascular physical mass which is carried in the circulation until it reaches a vessel too small to permit its further pasage when occlusion occurs

Question 20

what are the different types of embolism?

Answer 20

• most are derived from a thrombus - called **thromboembolism **- may be pulmonary or systemic
• other rare forms exist - FAT BAT
• fat, air or gas, thrombus, bacteria emboli, amniotic fluid, tumour fragments

Question 21

what is a pulmonary embolism?

Answer 21

• venous thrombi in the leg veins can travel to the lungs

Question 22

explain the difference in effects that a small vs larger pulmonary emboli can cause?

Answer 22

• small emboli may cause no effects
• larger emboli can cause chest pain, shortness of breath, infarction and sudden death

Question 23

what is a systemic embolism?

Answer 23

• embolism in the systemic system
• may airse in the heart or from atherimateous plaques
• may travel to various sites and cause TIA or stroke, ischaemic bowel etc

Question 24

what is ischaemia?

Answer 24

a **deficient supply of blood **- imbalance between perfusion and demand of oxygenated blood to a tissue

Question 25

what is ischaemia characterised by?

Answer 25

• by an insufficiency of O2, lack of nutrient substrates and inadequate removal of metabolites

Question 26

what tissues are susceptible to ischaemia?

Answer 26

• kidney and spleen
• organs with a high metabolic rate - eg the heart

Question 27

what is infarction?

Answer 27

• an area of ischaemic necrosis caused by occlusion of either the arterial supply or the venous drainage in a particular tissue
• almost all infarcts are due to a **thrombotic / embolic events **

Question 28

what is myocardial infarction?

Answer 28

decreased blood flow to the myocardium caused by an occulsion of the coronary arteries (which supply the myocardium)

Question 29

what is a cerebrovascular accident (infarct) or a stroke?

Answer 29

due to occulsion of the blood supply in the cerebrovascular circulation

Question 30

what is a pulmonary infarction?

Answer 30

• occurs when there is a complete obstruction in the pulmonary circulation

Question 31

what are examples of causes of ischaemia and infarction?

Answer 31

• thrombosis - most
• embolus - most
• local vasospasm
• extrinsic compression of vessel

Question 32

comapre hypoxia to ischaemia

Answer 32

• hypoxia - oxygen deficiency, causes cell injury
• ischaemia - hypoxia of tissue due to loss of blood supply due to occluded arterial flow or venous drainage

Question 33

what is the **most common cause **of hypoxia?

Answer 33

ischaemia