thrombosis, embolism, ischaemia and infarction Flashcards
what 2 factors mean that clots are rare?
Laminar flow – cells travel in the centre of arterial vessels and don’t touch the sides
Endothelial cells which line vessels are not ‘sticky’ when healthy
what is thrombosis?
the formation of a solid mass from blood constituents in an intact vessel in a living person .
outline how a thrombus is formed
- endothelial wall damaged
- platelets stick to the exposed collagen and release chemicals which cause platelet aggregation.
- trapped RBCs + clotting factors + platelets trigger the clotting cascade and a large protein molecule fibrin forms and deposits and forms the clot
what type of feedback loop is the formation of a thrombus?
Positive feedback loop - once started, difficult to stop
what is Virchow’s triad?
summarised the 3 causes of thrombosis:
- change in vessel wall eg. endothelial injury
- change in Blood flow (stasis of blood)
- change in blood constituents eg. hyper coagulation
what can be prescribed to reduce the risk of thrombosis?
Low dose aspirin
because it inhibits platelet aggregation
what is an embolism?
the process of a solid mass in the blood being carried through the circulation to a place where it gets stuck and blocks the vessel
define an embolus
a mass of material in the vascular system able to become lodged within a vessel and block it
give 5 examples of causes of an embolism?
- part of a thrombus that has broken off
- Air (pressurised systems of intravenous fluids/ bloods)
-a Tumour
-Amniotic fluid (rare in pregnant women)
-Fat (severe trauma with fractures)
what happens if an embolus enters the venous system?
An embolus in the venous system will go onto the vena cava and then through the pulmonary arteries and become lodged in the lungs causing a pulmonary embolism. This means there is decreased perfusion to the lungs.
what happens if an embolus enters the arterial system
it can travel anywhere downstream of its entry point.
The consequences could be stroke, MI, gangrene etc.
what is the most common cause of:
a) an arterial thrombosis?
b) a venous thrombosis?
a) an atheroma (plaque of fatty material built up inside arteries)
b) blood stasis (abnormal blood flow, blood not reaching areas of the body it should)
how do arterial/venous thrombosis differ in terms of :
a) pressure
a) main constituents of the thrombus
c) treatment
a) arterial has high pressure, venous has low pressure
b) arterial thrombus is made of platelets (white thrombus) whilst venous is made of coagulation factors (red thrombus)
c) arterial treated with antiplatelets drugs eg. asprin, venous treated with anticoagulants eg. warfarin
define ischemia
reduction of blood flow to a tissue without any other implications
define infarction
a reduction of blood flow to a tissue that is so reduced that it cannot even support mere maintenance of the cells in that tissue so they die
define end artery supply
an organ that only receives blood supply from one artery.
why are end artery supplies problematic?
if a thrombus forms In it, the whole blood supply to that organ is cut off, leading to infarction.
name 3 organs that have multiple arterial supplies
- Pulmonary arteries and bronchial arteries supplying the lungs
- Portal vein and hepatic artery supplying the liver
- Some parts of the brain – circle of Willis
what is deep vein thrombosis?
a deep venous thrombosis of the leg veins, breaks off and causes embolism through the large veins (inferior vena cava) and right side of the heart to the lungs
what are the 5 stages in clot formation
- vascular spasm
- platelet plug - aggregation
- coagulation
- clotting
- fibrinolysis
Damage to endothelial cells in the vessel causes some of the cells to lift away from the vessel wall, and expose what?
collagen
how do platelets adhere to the collagen?
Platelets adhere to collagen via von Willebrand factor (vWF) plasma protein secreted by endothelial cells (glycoprotein-1b)
what chemicals do platelets secrete once they are adhered to the collagen, which causes platelet aggregation and the formation of the platelet plug ?
ADP and thromboxane-A2
describe the intrinsic coagulation pathway in forming a thrombus
- RBCs and clotting factors get trapped within the aggregating platelets
- cascade: 12→11→9→9a+8→10→prothrombin activator
- prothrombin activator converts prothrombin 2 → thrombin 2a
- thrombin creates positive feedback loop, and activates soluble fibrinogen to polymerise into insoluble fibrin. clotting factor 13 is activated and forms crosslinks between the fibrin strands, creating the fibrin mesh ( ie. the thrombus)
describe the extrinsic coagulation pathway in forming a thrombus
Tissue factor 3 migrates from tissue into blood vessel
3→7→9 and then same as intrinsic cascade to form a fibrin polymer
what is a thrombus composed of mainly?
fibrin
What can happen if ischaemia is rectified?
Re-perfusion injury can occur due to the release of waste products.
Through which blood system would an embolus have travelled if it resulted in a pulmonary embolism?
venous system
