22.6
動脈硬化 I: はじめに
動脈硬化は、動脈の内壁にプラークが蓄積し、時間の経過とともに動脈が狭く硬くなる進行性の疾患です。これらのプラークは、脂質、カルシウム、血液成分、炭水化物、そして線維組織から構成されています。このプロセスは主に大動脈および中程度の大きさの動脈の内膜に影響を及ぼし、動脈の血流を減少させます。
病因とリス…
アテローム性動脈硬化症は、大動脈および中大動脈の内膜内に脂質、カルシウム、および線維組織からなるアテロームまたはプラークが蓄積することを特徴とする進行性疾患であり、動脈が硬化して狭くなります。
病因には、高血圧、低密度リポタンパク質またはLDLのレベルの上昇、喫煙、および内皮損傷の一因となる関節炎などの炎症状態が含まれます。
損傷した内皮はLDLの浸潤を可能にし、それが酸化して炎症を引き起こします。
単球は動脈壁に移動し、酸化したLDLを摂取するマクロファージに変化し、泡沫細胞を形成します。これらの泡沫細胞は脂肪線に集まり、アテローム性動脈硬化症の初期段階を示します。
泡沫細胞が蓄積し、炎症が持続すると、アテローム性動脈硬化性プラークが発生します。コレステロール、泡沫細胞、細胞老廃物、カルシウム、および繊維状キャップで構成されています。
時間の経過とともに、これらのプラークは拡大して硬化し、動脈狭窄と呼ばれる状態を引き起こします。
プラークの安定性はさまざまです。不安定なプラークには細い繊維状のキャップがあり、破裂して血小板を引き付け、血栓形成を引き起こす可能性があります。
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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.