Atheroma, thrombosis and infarction Flashcards
Thrombosis definition
A solid mass of blood constituents formed within an intact vascular system during life
Embolus definition
A mass of material in the vascular system able to become lodged within a vessel and block it
Ischaemia definition
A reduction in blood flow
Infarction definition
Reduction in blood flow with subsequent death of cells
Reperfusion injury definition
Tissue damage caused when blood supply returns to tissue after a period of ischaemia
End artery supply definition
Only one artery into a certain organ
Atherosclerosis definition
A disease of the arteries characterised by the deposition of fatty material on their inner walls and forming yellow plaques
What do platelets contain?
- Alpha granules - Involved in platelet adhesion to damaged vessel walls. Substances include fibrinogen, fibronectin and platelet growth factor
- Dense granules - Contain substances like ADP which cause aggregation
What is the difference between a thrombus and a clot?
A clot is coagulated blood outside of the vascular system if the vessel has been cut, or after death. A thrombus is the solidification of blood contents within the vascular system during life, often when there is endothelial damage but the vessel is intact.
How does a thrombus form?
- Platelets are activated
- Platelets release chemicals causing aggregation and initiate the clotting cascade (+ve feedback loops)
- Formation of fibrin mesh which traps RBCs
What is Virchow’s Triad?
The 3 things which predispose to thrombus formation:
- Changes in the vessel wall
- Changes in blood flow
- Changes in blood constituents
Give 4 potential events after thrombosis
- Lysis and resolution of the thrombus but with potential organ damage
- Organisation and repair of scar tissue
- Recanalisation with capillaries growing through
- Embolisation
Give 4 ways to prevent a thrombus forming
- Exercise/movement
- Elastic stockings/DVT stockings
- Aspirin
- Warfarin in severe cases
What effects can venous emboli have?
Form pulmonary embolisms:
- Smaller emboli may accumulate to cause idiopathic pulmonary hypertension
- Slightly larger emboli may cause acute respiratory and cardiac problems
- Massive emboli result in sudden death
What effects can arterial emboli have?
- Can travel to the brain causing a cerebral infarct (stroke)
- Can travel to the kidneys causing a renal infarct
- Can travel to the gut causing ischaemic bowel
- Can travel to the foot causing ischaemic foot (dry gangrene)
What 2 factors determine the extent of tissue damage in ischaemia?
- Duration of ischaemic period
2. The metabolic demands of the tissue
Why do reperfusion injuries occur?
Transport mechanisms are disrupted which causes ischaemic cells start producing waste products like superoxide radicals which damage cells on reperfusion
How can you minimise reperfusion injuries?
- Inducing comas
- Keeping the patient cool
Which organs are at greatest risk of infarction?
Ones with only one artery supplying them (end artery supply)
Which organs have duel artery supply and which arteries supply them?
- Liver – portal venous and hepatic artery supply
- Lung – pulmonary venous and bronchial artery supply
- Brain (some parts) – circle of Willis with multiple artery supplies
What is a watershed area?
An area which is the boundary between two adjacent arterial territories so it is susceptible to infarction if the blood pressure falls
Why is the heart similar to a watershed area?
Blood supplying the myocytes comes from outside the heart (coronary arteries) so low pressure can cause a sub-endocardial infarct
Where do atherosclerotic plaques form?
In high pressure systemic arterial areas such as the aorta and coronary arteries. Often occurs at arterial bifurcations
Give 6 risk factors for atherosclerosis
- Cigarette smoking
- Hypertension
- Poorly controlled diabetes
- Hyperlipidaemia
- Increasing age
- Being male
Name some complications of atherosclerosis
- Cerebral infarction
- Carotid atheroma
- Myocardial infarction
- Aortic aneurysm
- Peripheral vascular disease
- Gangrene
What are fatty streaks?
The earliest significant lesions formed by lipid-laded macrophages
Describe the stages of plaque formation
- Endothelial cells of the vessels are damaged
- Platelets aggregate and a thrombus forms
- Endothelial cells grow over a thrombus to repair it
- Haemorrhage and more damage occurs in the plaque making it larger
- Artery is partially occluded causing symptoms like unstable angina
- Artery is fully occluded so little/no blood can pass through - causes conditions such as MIs
Name 4 factors that can damage the endothelium
- Free radicals
- Nicotine
- Carbon monoxide (from smoking)
- Shearing forces from hypertension
How can you treat and prevent atherosclerosis?
- Stop smoking
- Control blood pressure
- Reduce weight
- Low does aspirin
- Statins
