Lecture 6 - Atheroma Flashcards
Define Atheroscelrosis
-The thickening and hardening of large and medium sized arteries, as a consequence of atheroma, beginning in the intima, progressing to the media
Define atheroma
The accumulation of intracellular and extracellular lipid in the intima and media of medium and large sized vessels
Define Arteriosclerosis
-The thickening and hardening of the walls of small arteries and arterioles (especially in the kidney), usually as a result of hypertension or diabetes mellitus
Define Monkeberg’s disease
-Uncommon calcification of the media of large arteries
What are the two major risk factors for atherosclerosis?
- Age
- Nutrition (high blood cholesterol)
What are the three types of lesion in atherosclerosis?
- Fatty streak
- Simple plaque
- Complex plaque
Describe the pathogenesis of atherosclerosis
1) Chronic endothelial injury leads to oxidised lipid droplets accumulating in the intima of arteries (transendothelial passage)
2) Endothelial dysfunction attracts monocytes which engulf the lipid and become foam cells. Gaps appear in the endothelium and platelets adhere. Monocytes and platelets secrete cytokines and growth factors which cause smooth muscles cell migration from the media (fatty streak formed)
3) Fatty streak grows into a simple plaque as the number of foam cells and smooth muscle cells increases, bulging of the endothelium occurs. Some smooth muscle cells lie beneath the endothelium and produce collagen, elastin and other matrix proteins producing a fibrous cap
5) The simple plaque progresses to a complex plaque: necrosis occurs, followed by the development of cholesterol crystals, calcification and vascularisation from the adventitia
What are the macroscopic features of a fatty streak?
-Yellow and slightly raised streak
What are the macroscopic features of a simple plaque?
- Raised yellow/white
- Irregular outline
Where does atherosclerosis often occur?
-In patches where flow is disturbed, such as around the opening of a branch
When do problems begin to arise in atherosclerosis pathogenesis?
-It is location dependant, can be as soon as 1-2mm in narrow arteries eg coronary
What is in the core of an atherosclerotic plaque?
-Necrotic and dead cells, debris and cholesterol clefts
Where does the majority of lipid come from which forms the plaques in atherosclerosis?
-Low density Lipoproteins
What happens when ulceration of the fibrous cap of a atherosclerotic plaque occurs?
-Fibrous cap is eroded from underneath and the core is exposed which can lead to thrombosis
When can thrombosis of an atherosclerotic plaque occur?
- When there is ulceration and rupture of the fibrous cap
- When gaps appear between endothelia
How can atheromatous emboli occur?
-Part of the atheroma can break up and move to distal site where it can cause an occlusion
What is the result of calcification of the plaque?
-Increases the stiffness of the arteries
How does haemorrhage of an atherosclerotic plaque occur?
-One of the vessels from vascularisation may break and haemorrhage into the plaque, causing it to break open
Why can aneurysms occur from atherosclerotic plaques?
-Loss of elastic tissue leading to permanent abnormal dilation
Define aneurysm
-Local dilatation of an artery due to weakening of the arterial wall
What is the most frequent cause of aneurysms in large arteries?
-Secondary to atherosclerosis
What is a dissecting aneurysm?
- Occur in the aorta and its branches; the initma tears open and blood flows into the media and separates the two layers
- Usually fatal and occur in a couple of minutes
Is atherosclerosis reversible?
-Upto a point - fatty streaks can disappear and plaques can shrink if a low cholesterol diet is instituted
Is atherosclerosis symptomatic?
-No, usually silent until a complication with the plaque arises
