thrombosis and haemostasis Flashcards
what is haemostasis?
- 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
what is thrombosis?
- 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
what is a thrombus?
- an aggregate of **coagulated blood **containing **platelets, fibrin and entrapped cellular elements **
what are the predisposing factors of thrombus formation?
virchow’s triad
* 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 **
what is the normal blood flow pattern?
laminar flow - cellular elements flow centrally in the vessel lumen
how can a change in endothelial surface lead to thrombus formation?
- 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
what can happen as a result of turbelent flow of blood?
- disrupted flow brings platelets into contact with the endothelium
- prevents dilution of activated clotting factors by flowing blood
what is hypercoagulability & what can cause it?
- 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)
what is the stasis of blood?
stoppage or slow down in the flow of blood
what can cause thrombosis in the venous system?
most commonly due to stasis
what is an atheroma?
a fatty material that builds up in your arteries
what kind of people are at risk for arterial thrombosis?
- smokers
- people with high cholesterol
why does an atheroma not occur in the venous system?
as the blood pressure is lower
where in the veins do thrombosis occur?
the valves
what are the risk factors for venous thrombosis?
- immobility eg after surgery, deep vein thrombosis could occur
- smoking
- cancer - can cause hypercoagulability
- pregnancy
- oestrogen therapy eg birth control or hrt
- dehydration
how does a arterial thrombus present?
- loss of pulse
- pale, cold extremities
- painful
- death and gangrene of the affected limb or site
how does a venous thrombus present?
- tender
- swollen
- reddened
- 95% occur in leg veins
what can happen ton a thrombus once it is formed?
- 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
what is an embolism?
- 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
what are the different types of embolism?
- 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
what is a pulmonary embolism?
- venous thrombi in the leg veins can travel to the lungs
explain the difference in effects that a small vs larger pulmonary emboli can cause?
- small emboli may cause no effects
- larger emboli can cause chest pain, shortness of breath, infarction and sudden death
what is a systemic embolism?
- 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
what is ischaemia?
a **deficient supply of blood **- imbalance between perfusion and demand of oxygenated blood to a tissue
what is ischaemia characterised by?
- by an insufficiency of O2, lack of nutrient substrates and inadequate removal of metabolites
what tissues are susceptible to ischaemia?
- kidney and spleen
- organs with a high metabolic rate - eg the heart
what is infarction?
- 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 **
what is myocardial infarction?
decreased blood flow to the myocardium caused by an occulsion of the coronary arteries (which supply the myocardium)
what is a cerebrovascular accident (infarct) or a stroke?
due to occulsion of the blood supply in the cerebrovascular circulation
what is a pulmonary infarction?
- occurs when there is a complete obstruction in the pulmonary circulation
what are examples of causes of ischaemia and infarction?
- thrombosis - most
- embolus - most
- local vasospasm
- extrinsic compression of vessel
comapre hypoxia to ischaemia
- hypoxia - oxygen deficiency, causes cell injury
- ischaemia - hypoxia of tissue due to loss of blood supply due to occluded arterial flow or venous drainage
what is the **most common cause **of hypoxia?
ischaemia
