atherosclerosis by dr. abdelaty shawky associate professor of pathology
TRANSCRIPT
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ATHEROSCLEROSISBy
Dr. Abdelaty ShawkyAssociate professor of pathology
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Histology of the vascular wall
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Endothelial cells
• Single cell-thick, continuous lining of the entire cardiovascular system, collectively called the endothelium.
• Endothelial structural and functional integrity is fundamental to the maintenance of vessel wall homeostasis and normal circulatory function.
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Smooth muscle cells• SMCs are predominant cellular element of the
vascular media• SMCs are responsible for vasoconstriction and
dilation in response to normal or pharmacologic stimuli.
• SMCs are important elements of both normal vascular repair and pathologic processes such as atherosclerosis
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Arteriosclerosis Arteriosclerosis literally means "hardening of the arteries”. It is a
term for thickening and loss of elasticity of arterial walls. Three
patterns are recognized:
1 .Atherosclerosis: the most frequent and important pattern.
2 .Mönckeberg medial calcific sclerosis: is characterized by calcific
deposits in muscular arteries in older people .
3 .Arteriolosclerosis: affects small arteries and arterioles. Is seen
with hypertension and diabetes mellitus.
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Atherosclerosis* Definition: Generalized, degenerative arterial disease
characterized by patchy thickening of the intima by
atheromas, which protrude into and obstruct vascular
lumens and weaken the underlying media.
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* Risk factors for atherosclerosis:
I. Non-modifiable risk factors:
• Genetic predisposition: Family history is the most important
independent risk factor for atherosclerosis. Certain genetic
disorders are strongly associated with atherosclerosis e.g.,
familial hypercholesterolemia.
• Age: Atherosclerosis manifests in middle and old ages.
• Gender: Atherosclerosis is less common in pre-menopausal
females than males, however is more common in post-
menoapsual females than males.
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II. Modifiable risk factors:
• Hyperlipidemia.
• Hypertension.
• Cigarette smoking.
• Diabetes.
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• Hyperlipidemia and, more specifically,
hypercholesterolemia—is a major risk factor for
development of atherosclerosis and is sufficient to
induce lesions in the absence of other risk factors. The
main cholesterol component associated with
increased risk is low-density lipoprotein (LDL)
cholesterol (“bad cholesterol”); LDL distributes
cholesterol to peripheral tissues.
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• By contrast, high-density lipoprotein (HDL)
(“good cholesterol”) mobilizes cholesterol from
developing and existing vascular plaques and
transports it to the liver for biliary excretion.
• Consequently, higher levels of HDL correlate
with reduced risk.
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* Pathogenesis of atherosclerosis:
Response to injury hypothesis:
It considers atherosclerosis to be a chronic
inflammatory response of the arterial wall
initiated by injury to the endothelium.
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1. Chronic endothelial injury induced by:
- Hypertension, Hyperlipidaemia, Cigarette
smoking….etc.
- This leads to endothelial dysfunction (increased
permeability to cholesterol, leukocyte adhesion.
2. Accumulation of lipoproteins: mainly LDLin the vessel wall.
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3. Adhesion of blood monocytes to the endothelium,
followed by their migration into the intima and their
transformation into macrophages which engulfs the
entering cholesterol and becomes foam cells.
4. Adhesion of platelets to the exposed sub-intimal
collagen.
5. Smooth muscle cell recruitment to the intima due
to release of mitogenic growth factors from activated
platelets and foam cells.
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6. Proliferation of smooth muscle cells in the
intima, and elaboration of extracellular matrix,
leading to the accumulation of collagen and
proteoglycans.
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Slide 12.13
Chronic endothelial “injury” theory
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Endothelial dysfunctionMonocyte adhesion and emigration2
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Macrophage activationSmooth muscle recruitment3
How to Make an Atheroma
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5, Well-developed plaque.
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* Gross and microscopic morphology:
1. Fatty spots: are the earliest lesion of atherosclerosis
as multiple yellow, flat spots less than 1 mm in diameter.
They are composed of lipid-filled foam cells.
2. Fatty streaks: fatty spots coalesce into elongated
streaks, 1 cm long or longer. They are not significantly
raised and thus do not cause any disturbance in blood
flow.
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Photomicrograph of fatty streak in an experimental hypercholesterolemic rabbit, demonstrating intimal macrophage-derived foam cells ( arrow).
Fatty streak—a collection of foam cells in the intima
Aorta with fatty streaks ( arrows).
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3. Atheroma (atherosclerotic plaque): consists of raised patches within the intima, having a soft, yellow, core of lipid, covered by a firm, white fibrous cap.
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* Microscopically:
Atherosclerotic plaques have three principal components:
1. Cells, including smooth muscle cells (SMCs), macrophages,
and other leukocytes
2. Extracellular matrix(ECM), including collagen, elastic
fibers, and proteoglycans
3. Lipid (LDL): intracellular (foam cells) and extracellular
(crystals)..
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The previously mentioned components are arranged in these layers :
1. Fibrous cap: in the top composed of SMCs and
relatively dense ECM, macrophages, and lymphocytes.
2. Necrotic core: Deep to the fibrous cap , containing
cholesterol clefts, necrotic debris from dead cells, foam
cells and fibrin.
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* Sites of atherosclerosis:
• Large elastic arteries e.g., aorta, carotid, and
iliac arteries.
• Large and medium-sized muscular arteries e.g.,
coronary, renal, and popliteal arteries are the
vessels most commonly involved by
atherosclerosis.
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* Complications:
1. Rupture, ulceration, or erosion of the luminal
surface of atheromatous plaques.
2. Atheroemboli.
May occur after rupture of atheromatous plaque which
may be fragmented into microemboli.
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3. Hemorrhage into a plaque may be initiated by
rupture of either the overlying fibrous cap or the thin-
walled capillaries that vascularize the plaque. A
contained hematoma may expand the plaque or induce
plaque rupture.
4. Thrombosis usually occurs on disrupted lesions
(those with rupture, ulceration, erosion, or
hemorrhage) and may partially or completely occlude
the lumen.
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5. Aneurysm: is abnormal dilatation of the
arterial wall which is induced by atrophy of the
underlying media, with loss of elastic tissue,
causing weakness, and potential rupture
6. Calcifications: Atheromas often undergo
calcification.
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Please take care of
atherosclerosis