22.6
Athérosclérose I : Introduction
L’athérosclérose est une maladie évolutive caractérisée par l’accumulation de plaques sur la paroi interne des artères, entraînant leur rétrécissement…
L’athérosclérose est un trouble progressif caractérisé par l’accumulation d’athéromes ou de plaques composées de lipides, de calcium et de tissu fibreux dans l’intima des artères de grande et moyenne taille, ce qui les fait durcir et rétrécir.
Les facteurs étiologiques comprennent l’hypertension, des niveaux élevés de lipoprotéines de basse densité ou LDL, le tabagisme et des affections inflammatoires comme l’arthrite, qui contribuent aux lésions endothéliales.
L’endothélium endommagé permet l’infiltration des LDL, qui s’oxydent et déclenchent l’inflammation.
Les monocytes migrent dans la paroi artérielle et se transforment en macrophages qui ingèrent des LDL oxydés, formant des cellules spumeuses. Ces cellules spumeuses se regroupent en stries graisseuses, marquant le stade précoce de l’athérosclérose.
Au fur et à mesure que les cellules spumeuses s’accumulent et que l’inflammation persiste, la plaque d’athérosclérose se développe. Il comprend du cholestérol, des cellules spulentes, des déchets cellulaires, du calcium et un capuchon fibreux.
Au fil du temps, ces plaques peuvent s’agrandir et durcir, provoquant un rétrécissement artériel, une condition connue sous le nom de sténose.
Les plaques varient en stabilité ; Les plaques instables ont un mince capuchon fibreux qui peut se rompre, attirer les plaquettes et provoquer la formation de thrombus.
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Q1: What is atherosclerosis and what causes it to develop?
Atherosclerosis is a progressive disorder characterized by accumulation of plaques comprising lipids, calcium, and fibrous tissue within large and medium-sized arteries, causing them to harden and narrow. Development involves multiple factors including hypertension, elevated LDL cholesterol, smoking, and inflammatory conditions that damage the endothelium and allow lipid infiltration.
Q2: How do foam cells form and what role do they play in atherosclerosis?
Foam cells form when monocytes migrate into the damaged arterial wall and transform into macrophages that ingest oxidized LDL cholesterol. These foam cells cluster together to create fatty streaks, marking the earliest visible stage of atherosclerosis and initiating plaque development through continued accumulation and inflammatory responses.
Q3: What is the difference between stable and unstable atherosclerotic plaques?
Stable plaques have a thick fibrous cap and restrict blood flow gradually, potentially causing angina. Unstable plaques have a thin fibrous cap that may rupture, attracting platelets and triggering thrombus formation, which can cause myocardial infarction or stroke by suddenly blocking blood flow.
Q4: How does endothelial damage initiate the atherosclerotic process?
Endothelial damage from hypertension, smoking, elevated LDL, and inflammatory conditions increases arterial wall permeability. This allows circulating lipoproteins to infiltrate the intima, where LDL undergoes oxidation and triggers an inflammatory response that attracts macrophages and initiates plaque formation and progression.
Q5: What happens during plaque progression and calcification in atherosclerosis?
As foam cells accumulate and inflammation persists, plaques enlarge and harden through calcification. Advanced lesions may undergo calcification, which hardens the plaque, reduces arterial elasticity, and increases rupture risk. Smooth muscle cells migrate into the intima and produce extracellular matrix components like collagen, contributing to plaque growth.
Q6: How does oxidized LDL trigger inflammation in atherosclerosis development?
When LDL infiltrates the damaged endothelium, it undergoes oxidation and triggers an inflammatory response. This attracts macrophages that transform into foam cells, which accumulate and exacerbate inflammation by releasing cytokines that promote smooth muscle cell migration and proliferation within the arterial intima.
Q7: What complications can result from atherosclerotic plaque narrowing or rupture?
Stable plaques that restrict blood flow can cause angina by reducing oxygen delivery. Ruptured plaques trigger thrombus formation, potentially causing myocardial infarction or stroke. Students should explore atherosclerosis clinical manifestations and diagnostic tests to understand how disease severity is assessed and complications are identified.