Atherosclerosis Flashcards
Where does atherosclerosis come from?
Greek- athero= paste
sclerosis= hardness
Coat thickens so much as to close up and stop blood movement
Why can atherosclerosis result in?
Heart attack, stroke and gangrene
Initially thought of and what is it now known as?
Initially- lipid storage disease
now- chronic inflammatory disease influenced by many factors= inflammatory cells and cytokines
Main problem with atherosclerosis
If the plaque ruptures- thrombosis formation and death
Pathogenesis
Lifestyle choices, medical conditions and haemodynamic of blood flow
begin at birth but develops over lifetime
often remains symptomless for majority of life until advanced
Risk factors
Modifiable- physical inactivity, stress, obesity, diabetes, dyslipidaemia, hypertension, smoking
Non- modifiable- genetics, gender, age, inflammation, family history
Distribution of atherosclerotic plaque
Found within the peripheral and coronary arteries
focal distribution along the artery length
-may be governed by haemodynamics= changes in tuburlance/flow
- alter gene expression
- areas prone to atherosclerosis
Atherosclerosis is composed of what
Complex lesion consisting of: lipids necrotic core connective tissue fibrous cap- made from SMC and ECM
What happens if the plaque occludes
restrict blood flow- angina
or it may rupture- thrombus formation/ death
Response to injury hypothesis of atherosclerosis
First suggested in 1856- Rudolph Virchow and updated by Russell ross in 1993/9
indicated by an injury in the endothelial cells which leads to endothelial dysfunction
What does healthy endothelium produce to protect against atheroma?
NO and other mediators which protect
alter NO biosynthesis- affects BP control, regional blood flow, predisposes to atherosclerosis
send signals to inflammatory cells which accumulate and migrate into the vessel, leading to inflammation
Stimulus adhesion
Chemoattractants
chemicals that attract leukocytes are released from the site of injure and a concentration gradient is produced
damaged EC also express adhesion molecules
the adhesion cascade
Capture rolling slow rolling firm adhesion transmigration - following down vessel wall and migrate through by chemoattractant
LDL passing though and out of the arterial wall- When?
when in excess, accumulate in the arterial wall- deliver cholesterol
What generate free radicals
Macrophages and EC
LDL is oxidised by and what happens?
free radicals (oxLDL)- engulfed by macrophages to form foam cells release more proinflammatory cytokines
Cytokines found in plaques
IL-1,6,8,IFN-g, TGF-b, MCP-1 and PDGF
Progression of atherosclerosis 1- fatty streaks, what happens?
- earliest lesion of atherosclerosis
- appear at very early age
- accumulation of lipid laden macrophages (foam cells) and T lymphocytes within the intimal layer of the vessel wall form fatty streaks
- damage endothelium- allow macrophages in
progression of atherosclerosis 2- intermediate lesions?
layers composed of:
- foam cells
- VSMC
- EC lipids and cholesterol
- T lymophocytes
- adhesion and aggregation of platelets to vessel wall
progression of atherosclerosis 3- protective mechanism
reverse cholesterol transplant
- pathway for plaque reduction involving HDL
- HDL contain apo-A1 interact with foam and collect cholesterol
- mature HL travels to liver and releases cholesterol
- HDL then recirculates back
progression of atherosclerosis 4- fibrous plaque or advanced lesion
- thought to need an added impetus= another risk factor or area of disturbed flow
- cytokine release cells cause SMC proliferation and deposition of connective tissue
- leads to dense fibrous cap
What is fibrous cap composed of?
ecm- collagen (strength) and elastin (flexibility)
Lipid core
Necrotic and apoptotic debris, smc, foam cells, macrophages, t lymphocytes
Cap and core=
Artheromatous plaque
What does the Artheromatous plaque do?
may be calcified
impedes blood flow
prone to rupture
bigger the plaque= more narrowing and pain
Cyles of vascular inflammation and LDL results in formation of necrotic cap
- LDL enters vessel wall
- macrophage engulf and LDL become foam cells
- LDL lysed, cholesterol released crystalizes
- crystals in the foam cells induce apoptosis
- extracellular lipid pool within the arterial wall
- further attraction of macrophages
Human coronary atherosclerotic plaque looks like
Yellow core
lipids separated from lumen by fibrous cap
opposite plaque is an arc of normal vessel wall
Progression of atherosclerotic plaque 5- plaque rupture
Plaque constantly growing and receding
fibrous cap- resorbed and redoposited in order to be maintained
increase VMSC and matrix proteins to stabalise
What does a large number of macrophages predispose the plaque to?
Rupture
increase matrix metalloproteinases and gelatinase- cap becomes weak and rupture provides a substrate for thrombus formation and vessel occlusion
Rupture can be induced by
Cholesterol crystallization
Large necrotic plaque can rupture with
Haemorrhage
plaque lap is tonr and leads to rupture
Small necrotic plaque rupture
Erosion - wearing away
plaque disruption
The torn cap projects into the lumen of the artery and thrombus is contained with the plaque core
Plaque rupture- why it happens?
thin fibrous cap collagen poor fibrous cap large lipid cap many macrophages fibrin rich thrombus
How does erosion happen?
prosteoglycan glycosaminoglycan rich little or no lipid core neutrophils and NETS many smooth muscle cells platelet rich thrombus
Mechanism of erosion
- resting endothelial cell
- activated endothelial cell
- sloughed endothelial cells
- resting platelet and grammalogue
- activated platelet and granulocyte
- rich platelet thrombosis
* disturbed flow
Lipoproteins
Lipids are transported around the body as these
General structure of lipoproteins
central core is hydrophobic lipid (triglyceride cholesterol) surrounded by hydrophilic (free cholesterol, phospholipids, apolipoproteins)
Lipids classification
According to density
- chylomicrons= ApoB-48, diameter 100-1000nm
- LDL- ApoB-100, diameter 20-30nm
- Very low density lipoproteins- ApoB-100 diameter 30-80nm
- HDL- APOA1/A2, diameter 7-20nm
Lipids transport by 3 pathways
- Exogenous- gut to liver, dietary
- endogenous- liver to cells
- reverse- cells to liver
Exogenous pathway
- Lipids are digested
- lipids assemble with apoplipoproteins B-48 into nascent chylomicrons
- chylomicrons move into liver and bloodstream, HDL donate apopliporteins C-11 and E- mature chylomion. AC-11 can only bind adipose and ApoE cannor bind hepatocytes
- LDL catalyses hydrolysis reaction releasing glycerol and fatty acid from chylomicrons- absorbed into tissue
- remnants are endocytosed and hydrolysed within lysosomes and this releases glycerol and fatty acid in the cell
Endogenous pathway
- triclylglycerol and cholesterol are assembled with apolipoprotein
- HDL donates apolipoprotein C-II and E
- Apolipoprotein C-II activates LDL, causing hydrolysis of VDL particles and the release of glycerol and fatty acids- these can be absorbed by adipose tissue and muscle
- the hydrolysed VLDL particles are now called IDL
IDL
Contain multiple AoE binding LDLR with high affinity