Lec 14 Atherosclerosis Flashcards
What is role of endothelial cells in normal vascular homeostasis?
- physical barrier to large molec
- secrete substances that are anti-inflammatory and promote vasodilation [NO] and resist thrombosis
= maintains homeostasis
What is role of smooth muscle cells in normal vascular homeostasis?
- effect vasoconstriction/ vasodilation in response to local/circulating molec = maintain vascular tone
- produce extracellular matrix to maintain vascular integrity
- contained within arterial media
What is role of collagen and elastin?
collagen maintains strength
elastin maintains flexibility
both produced by smooth muscle cells
What are the 3 layers of normal arterial wall?
intima = closest to lumen, consists of single layer endothelial cells
media = middle, bounded by elastin [internal and external elastic laminae], consists of smooth muscle cells and extracellular matrix
adventitia = outer, contains nerves, lymphatics, blood vessels
What makes up the extracellular matrix?
collagen + elastin + proteoglycans
maintain structural integrity of vessel
What is the earliest visible lesion of atherosclerosis?
fatty streak
What is the order:
plaque disruption
fatty streak
plaque progression
fatty streak –> plaque progression –> plaque disruption
What is mech/pathway of fatty streak?
- endothelial cell dysfunction: endothelial cell no longer physical barrier
- increased endothelial permeability allows entry LDL into intima where it stays in subendothelial space
- LDL gets modified [by oxidation or glycation] = mLDL
- mLDL promotes leukocyte recruitment and foam cell formation] + stimulates inflammation directly + indirectly
- recruitment leukocytes [monocytes + T cells] to vessel wall
- monocytes into intima –> become phagocytes –> take up mLDL to become foam cells via unregulated scavenger receptor
- foam cell apoptosis, necrosis, persistent inflammation = make up core of plaque formation
What are risk factors for initial endothelial cell dysfunction that leads to fatty streak/atherosclerosis formation?
smoking, high cholesterol, diabetes
associated with hydrodynamic stress –> high BP, branch points in vessels
How does mutated apolipoprotein B lead to atherosclerosis?
b/c it allows easier entry of LDL into the subendothelial space
What is the necrotic core?
lipid rich center of a plaque formed by necrotic foam cells
When do fatty streaks appear?
start to appear in early life, by late teens can be found but are asymptomatic
What is mech/pathway of plaque progression?
-
What happens in early plaque growth?
have outward remodeling of arterial wall to preserve diameter of lumen and does not limit blood flow so you don’t get ischemic symptoms
What happens in later plaque growth?
over time vessel can no longer compensate with outward remodeling –> start to restrict vessel lumen and impede perfusion –> tissue ischemia –> symptoms like angina or claudication of extremities
What is underlying pathology of most coronary syndromes?
fibrous cap of an atherosclerotic plaque ruptures –> exposes prothrombic molec within lipid core and precipitates actual thrombus that occludes arterial lumen
What is mech/pathways of plaque progression from fatty streak to fibrous plaque?
- smooth muscle cells migrate from arterial media into intima and proliferate [signaled by foam cells, platelets, endothelial cells]
- smooth muscle cells secrete collagen/extracellular matrix to form fibrous cap on plaque
- T-lymphocyte IFN-g inhibits smooth muscle collagen synthesis + local foam cells secrete MMP both degrade fibrous cap
- balance betwen cap degradation in synthesis results in stable vs vulnerable plaque
What are characteristics of stable vs vulnerable plaque?
stable = small lipid pool thick fibrous cap, preserved arterial lumen
vulnerable = large lipid cores, thin fibrous cap, many inflammatory cells
What happens in plaque disruption?
- fibrous cap ruptures due to hemodynamic stress and matrix degradation
- subsequent development of superimposed thrombus consisting of fibrin, RBCs, platelets
- clinical manifestion depends on vascular territory and stability of overlying thrombus = rupture may heal and just narrow lumen [=silent] or may cause complete occlusion and major event [ex. MI]
Why higher risk of MI in the morning?
higher BP in the morning = more hemodynamic stress = more likely to plaque to rupture
What is order of location where atherosclerotic plaques happen first?
step1
ab aorta > coronary aorta > popliteal artery > carotid artery
What are traditional non-modifiable risk factors of atherosclerosis?
step1
- age [older]
- gender [male or post-menopausal female]
- family history
What are modifiable risk factors for atherosclerosis?
step1
- smoking
- hypertension
- hyperlipidemia
- diabetes
- physical inactivity
What are gender risk factors for atherosclerosis?
step1
higher risk in men and in post-menopausal women
