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| | ==Degeneration== | | ==Degeneration== |
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| − | ===Arteriosclerosis=== | + | ===[[Arteriosclerosis]]=== |
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| − | Encompasses a group of diseases characterised by degeneration of the arterial walls with fibrous thickening. The disease is chronic and non-inflammatory. As the vessels lose their elasticity the lumen becomes narrowed and the end result is ischaemia if the tissue bed supplied.
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| − | [[Image:Arteriosclerosis.jpg|right|thumb|125px|<small><center>'''Arteriosclerosis'''. Courtesy of A. Jefferies</center></small>]]
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| − | ''Incidence:''
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| − | *Horse: mainly in the aorta and branch points of arteries.
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| − | *Dog: commonly seen in th myocardium. Contributes to myocardial scarring and damage preceding myocardial failure.
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| − | *Also occurs in cattle.
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| − | Thought to be aetiologically related to haemodynamic damage to the endothelial layer. Perhaps initiated by:
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| − | *Platelet endothelial interaction.
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| − | *Plasma constituents entering the sub-endothelial layer.
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| − | Changes may be:
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| − | ====Hyperplastic====
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| − | Chronically raised intraluminal pressure stimulates hyperplasia of the smooth muscle layer, reducing the size of the vessel lumen.
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| − | The elastic lamina may become duplicated or split allowing penetration of hyperplastic smooth muscle cells into the intima. Fibrous plaques form.
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| − | ====Hyaline====
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| − | [[Image:Arterial hyalinisation.jpg|right|thumb|125px|<small><center>'''Aterial hyalinisation'''. Courtesy of A. Jefferies</center></small>]]
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| − | May occur alongside hyperplastic lesions or alone as a primary lesion. The intima becomes more permeable, allowing penetration of plasma contents into the vessel wall which becomes degenerate.
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| − | A combination of hyerplastic and hyaline change is often seen in the coronary arteries of the dog. Associated with ischaemic necrosis of the myocardium and therefore heart failure.
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| − | Also seen in uterine and ovarian arteries of pregnant animals. Thought to be clinically insignificant but indicated raised intraluminal pressure.
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| | ===Atherosclerosis=== | | ===Atherosclerosis=== |