Atherosclerosis, thrombosis, embolism and infarction Flashcards
Define atherosclerosis
- Athere = gruel; Sclerosis = hardness
- Literal meaning is hardening of the arteries
What arteries does atherosclerosis mainly affect?
- Elastic arteries
- Medium to large muscular arteries
Describe atheromas
- Fibro-fatty plaques
- Intimal fibrous cap
- Central core rich in lipids
What are the risk factors for atherosclerosis?
- Age - older –> higher risk
- Sex - male more common
- Genetics
- Hyperlipidaemia
- Hypertension
- Smoking
- Diabetes mellitus
What are the risk factors for atherosclerosis?
- Age - older –> higher risk
- Sex - male more common
- Genetics
- Hyperlipidaemia
- Hypertension
- Smoking
- Diabetes mellitus
What is involved in the pathogenesis of atherosclerosis?
- Chronic endothelial injury/dysfunction
- Role of lipids
- Role of macrophages
- Smooth muscle proliferation
- Formation of a fibro-lipid plaque
- Injury to the plaque - thrombus formation
Causes of chronic endothelial injury/dysfunction
- Haemodynamic disturbances
- Hypercholesterolemia
- Hypertension
- Smoking
- Toxins
- Viruses
- Immune reactions
What happens in chronic endothelial injury/dysfunction?
- Leukocyte adhesion
- Increases production of vascular cell adhesion molecule 1 (VCAM-1), intercellular adhesion molecule 1 (ICAM-1), P-selectin, E-selectin
- These molecules cause more monocyte adhesion and increased endothelial permeability therefore increased monocyte migration ending up in tunica intima
What role do lipids play in atherosclerosis?
Hyperlipidaemia (LDL cholesterol):
- Impairs endothelial function
- Accumulates within intima
- Causes oxidative modification of LDL:
- ingested by macrophages via SCAVANGER receptors = foam cells
- chemotactic for monocytes
- inhibit the motility of macrophages
- stimulates release of cytokines
- cytotoxic to endothelial and smooth muscle cells
What is the role of macrophages in atherosclerosis?
-Engulf oxidised LDL = foam cells
-Secrete:
IL1 (interleukin 1)
TNF (tumour necrosis factor)
MCP1 (monocyte chemotactic protein 1)
Growth factors (PDGF, FGF, TNF)
Interferon alpha, TGF-beta
-These secretions cause further attraction of monocytes into intima and phagocyte more LDL cholesterol
What is the role of macrophages in atherosclerosis?
-Engulf oxidised LDL = foam cells
-Secrete:
IL1 (interleukin 1)
TNF (tumour necrosis factor)
MCP1 (monocyte chemotactic protein 1)
Growth factors (PDGF, FGF, TNF)
Interferon alpha, TGF-beta
-These secretions cause further attraction of monocytes into intima and phagocyte more LDL cholesterol
-Fatty streaks appear
What does LDL cholesterol stand for?
Low-density lipoprotein cholesterol
What does LDL cholesterol stand for?
Low-density lipoprotein cholesterol
Role of smooth muscle proliferation
- Fatty streaks mature into mature fibro-fatty atheroma
- Smooth muscle proliferates which helps in the formation of fibrous tissue causing the fibrous cap
- In the centre, the immobile foamy cells will eventually die
- Once these cells are dead, LDL cholesterol crystallises and groups together in the centre forming lipid necrotic debris
Why is it good to include antioxidants in one’s diet?
Prevents LDL from being oxidised so cannot be engulfed by macrophages
Why is it good to include antioxidants in one’s diet?
Prevents LDL from being oxidised so cannot be engulfed by macrophages
What causes smooth muscle to migrate to tunica intima?
Cytokines and growth factors released by the foam cells
Morphology of atheroma
- Atheromatous (fibro-fatty, fibro-lipid) plaque
- Patchy and raised white to yellow 0.3-1.5cm
- Core of lipid
- Fibrous cap
Which vessels are most commonly affected?
- Abdominal aorta
- Coronary arteries
- Popliteal arteries
- Descending thoracic aorta
- Internal carotid arteries
- Vessels of the circle of Willis
What complications can take place with atheromas?
- Calcification
- Rupture or ulceration
- Haemorrhage
- Thrombosis
- Aneurysmal dilatation
Clinical issues if complications happen
- Thrombosis
- Calcification
- Aneurysmal dilatation
- Ischaemic events: heart, brain, lower extremities, other organs
What are primary preventions of atherosclerosis?
- Stop smoking
- Control hypertension
- Weight reduction
- Lowering total LDL
- Reduce calories intake
What are primary preventions of atherosclerosis?
- Stop smoking
- Control hypertension
- Weight reduction
- Lowering total LDL
- Reduce calories intake
What are secondary preventions of atherosclerosis?
- Prevent complication
- Antiplatelet drugs in thrombosis
- Lower blood lipid levels
What are lipoproteins?
Central core of hydrophobic lipid
-triglycerides or cholesterol esters
Hydrophilic coat of polar substances
- phospholipids
- free cholesterol
- associated proteins - apoproteins or apolipoproteins
How do the 5 main lipoprotein classes vary?
- core lipids
- apoproteins
- size
- density
What are the 5 main classes of lipoproteins?
- High density lipoprotein (HDL)
- Intermediate density lipoproteins (IDL)
- Low density lipoproteins (LDL)
- Very low density lipoproteins (VLDL)
- Chylomicrons
How do the lipoproteins interact with cholesterol?
Chylomicrons transport triglycerides and cholesterol esters from the GI to tissues
- Split by lipoprotein lipase to release free fatty acids (FFAs)
- FFAs taken up by muscle and adipose tissue
Chylomicron remnants taken up in the liver
-cholesterol stored, oxidised to bile acids or released to VLDL
VLDL transport cholesterol and newly synthesised triglycerides to tissues
-TGs removed from VLDL leaving LDL with a high cholesterol (taken up by cells or liver)
HDL absorbs cholesterol from cell breakdown and transfers it to VLDL and LDL
What is hyperlipidaemia?
An increase in the plasma concentration of lipids
What are the dangers of plasma cholesterol and LDL?
Increased plasma cholesterol associated with increased LDL is a risk factor for atheromatous disease
-may lead to atherosclerosis, ischaemic heart disease, myocardial infarction & cerebral vascular accidents
What are the dangers of plasma cholesterol and LDL?
Increased plasma cholesterol associated with increased LDL is a risk factor for atheromatous disease
-may lead to atherosclerosis, ischaemic heart disease, myocardial infarction & cerebral vascular accidents
What is the average total cholesterol level in the UK?
5.7mmol/L
What is the ideal cholesterol level?
<5mmol/L
What is a mildly high cholesterol level?
5 to 6.4mmol/L
What is a moderately high cholesterol level?
6.5 to 7.8mmol/L
What is a very high cholesterol level?
> 7.8mmol/L
What else other than the cholesterol level must be taken into account when determining how high cholesterol is?
- the ratio between good (HDL) and bad (LDL) cholesterol
- other risk factors for cardiovascular disease e.g. smoking, diabetes, high blood pressure
How do lipid lowering drugs work?
- Reducing production of lipoproteins or
- Increasing their removal from the blood
What is the aim when using lipid lowering drugs?
Reduce plasma cholesterol
- Lifestyle modification (diet and exercise) is first step
- Drug therapy should be secondary
What 3 source is cholesterol derived from?
- De novo synthesis in liver
- Uptake from circulating LDLs
- Uptake of chylomicron remnants
What are the actions of different drug types?
- Sequester bile acids in the intestine/Decrease hepatic stores of cholesterol e.g colestyramine
- Inhibit transport protein for cholesterol in the brush border of enterocytes in the duodenum e.g ezetimibe
- Alter the levels of plasma lipoproteins e.g fenofibrate, bezafibrate, gemfibrozil & nicotinic acid
- Inhibit the synthesis of cholesterol in the liver e.g simvastatin, pravastatin, atorvastatin, rosuvastatin
How does cholestyramine affect cholesterol levels?
- Binds to bile in intestine
- More bile excreted out, less goes into liver
- Cholesterol then used to increase bile levels in liver causing a decrease in cholesterol levels