Thrombosis and Infarction Flashcards
Define clot
Solid mass of blood constituents formed after death
Define thrombus
Solid mass of blood constituents formed in life
3 predisposing factors (Virchows triad)
Changes in flow, change to vessel wall, changes in blood constituents
Define embolism
Process of a solid mass in the blood being carried through the circulation until it causes an occlusion
6 causes of embolus
Fat, air, thrombus, bacteria, amniotic fluid, tumour
2 reasons clots are rare
Laminar flow (cells travel in centre of vessels and don’t touch the sides). Endothelial cells that line vessels are not ‘sticky’ when healthy
2 stages of thrombosis
Platelet aggregation and clotting cascade
Define ischaemia
Reduction in blood flow to a tissue without any implications
Define infarction
Reduction in blood flow to a tissue to the point that it can not support the demands of the cells so they die
3 organs with dual blood supply
Liver - portal venous and hepatic artery. Lung - pulmonary veins and bronchial arteries. Brains - Circle of Willis
Describe the course of arterial thrombosis
Atheromatous plaque consisting of a slightly raised fatty streak, protrudes into lumen causing turbulence, this causes loss of intimal cells. Turbulence predisposes to fibrin deposition and platelet clumping. Collagen is exposed & platelets settle
How are lines of Zahn formed?
Alternating layers of platelets and a fibrin meshwork in which RBC get trapped
What initiates venous thrombosis?
Most begin at valves where there is natural turbulence, may be damaged by trauma, stasis or occlusion
When is venous thrombosis most likely?
Post surgery, when blood pressure is allowed to fall, following a MI, immobilisation,
What is thrombophlebitis?
When a thrombosed vein becomes inflamed
What is phlebothrombosis?
When an inflamed vein becomes thrombosed
Clinical signs of arterial thrombosis
Area of impaired supply becomes cold, pale and painful. Eventually the tissue dies and gangrene occurs
Clinical signs of venous thrombosis
Tender, swollen and red
Describe the structure of an atherosclerotic plaque
central lipid core, cap of fibrous tissue containing macrophages, mast cells and T lymphocytes
What is a thrombotic cerebral infarction?
Arterial thrombus due to atheroma in any of the vessels supplying the brain
What is a hypertensive stroke?
High blood pressure leads to atheroma and disruption of the autoregulation of cerebral circulation
5 risk factors for atheroma
Male, increased blood pressure, increased age, smoking, diabetes
What is a fatty streak?
Yellow elevation of intimal lining made up of lipid laden macrophages
3 stages of formation of atheroma
Fatty streak formation - lipids deposited, inflammation, increased permeability and white blood cell recruitment.
Fibrolipid plaque formation, lipid stimulates formation of fibrocollagenous tissue - thinning of muscular media.
Complicated atheroma - prone to rupture, may be calcified, rupture activates clot/thrombosis -> MI/angina
