29 - Atherosclerosis Flashcards
Definition
A common degenerative disease of the arteries
characterized by lipid deposition in the
subintimal Connective Tissue and fibrosis
forming intimal lesions called atheromas
(atheromatous plaques)
Predisposing factors:
- Non modifiable
- Modifiable
Non modifiable
Heredity (genetics)
Age : the incidence increased as the age advanced
Gender: More in Males till menopause then difference diminish.
Modifiable
Hyperlipidemia: high LDL, low HDL Hypertension Cigarette smoking Diabetes Mellitus Stress Diet: Excess intake of animal fats Other risk factors as inflammation, metabolic syndrome.
Pathogenesis
Traditionally
Insudation theory
Thrombogenic
theory
-response to injury theory: The model views atherosclerosis as a chronic inflammatory response of the
arterial wall to endothelial injury.Insudation theory:
Plasma passes constantly from the vascular lumen through the vessel wall. Repeated
endothelial cell injury increase endothelial permeability to plasma lipoproteins.
During its passage some of the large lipoprotein molecules are trapped in the
subintimal connective tissue. Eventually the protein part is filtered , while the
insoluble lipid part is retained and induce fibrosis around
Thrombogenic theory:
Small fibrin thrombi form all over the intimal surface and heal by organization.
When the thrombus is large its center degenerates and shows lipid derived from the
blood element within the thrombus.
Vascular response to injury
varies according to
- Type of injury
- Cells mediating the response (Players)
- Mechanism
Type of injury
May be biochemical, immunologic, or hemodynamic
Cells mediating the response (Players)
Endothelial cells
Smooth muscle cells of the vascular wall.
Mechanism
Vascular injury — endothelial cells loss or dysfunction –healing involve
migration of smooth muscle cells and their precursors to intima — proliferation
and secretion of extracellular matrix – neointima.
Sites:
Large elastic arteries: Aorta and its main branches (carotid and internal
iliac), commonly affected.
Medium sized muscular arteries (coronary, renal, and popliteal arteries) frequently affected
Pathological features
Grossly:
I: Fatty streaks
II. Atheromatous plaques:
Fatty streaks
Yellow may be slightly raised macules on the intimal surface that
coalescence into elongated lesion.
Composed of lipid filled macrophages in the subintimal connective tissue.
Start early in childhood (common by the age of 10 years)
No effect on blood flow
Atheromatous plaques:
White to yellow raised plaques or nodules 0.3 to 1.5 cm can coalescence
to form larger lesions.
due to intimal thickening and lipid accumulation then fibrosis around
deposited lipids
Atheromatous ulcers due to necrosis of the endothelium covering the
lesions.
Thrombi may be formed on top of rupture, erosion or ulceration of plaque.
Microscopically
Cholesterol and its esters are deposited in the subintimal connective tissue .
They are found free , inside smooth muscle cells derived from the media and
inside macrophages (foam cells). In paraffin sections the free cholesterol
crystals appear as needle shaped or rhombic shaped empty spaces
(dissolved).
Neovascularization ,fibrosis and hyalinosis of the subintimal connective
tissue around the deposited lipids.
Dark blue stained calcium granules deposited in old lesions.
Fragmentation of internal elastic lamina and atrophy of the media opposite
the atheroma
Effects and Complications: 1) In large elastic arteries:
a) Fusiform aneurysm due to loss of elasticity and atrophy of the media.
b)A thrombus over the atherosclerotic lesion gives rise to emboli causing infarcts in different
organs.
c) Dissecting aneurysm in the aorta.
Effects and Complications:
2) In medium and small arteries:
a) Narrowing of arteries causes ischemia especially heart, brain, kidneys and lower limbs.
b) Thrombosis of the arteries causes infarcts as myocardial infarction.
c) Atheromatous nodules in the cerebral arteries may cause pressure atrophy of the media
resulting in small aneurysms or rupture and hemorrhage.
