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| − | ==Atrophy== | + | ==[[Muscle Atrophy]]== |
| − | [[Image:Atrophic muscle fibres.jpg|right|thumb|100px|<small><center>Atrophic muscle fibres (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]] | |
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| − | *Decreased myofibre or whole muscle diameter
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| − | *Myofibrils removed by disintegration -> sacrolemma too large -> forms folds
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| − | *Caused by:
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| − | **<u>'''Disuse'''</u> (e.g. fracture, failure to use limb, recumbency)
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| − | ***Slower than denervation atrophy
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| − | ***Reversible unless too prolonger or severe to cause loss of myofibres
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| − | **<u>'''Denervation'''</u>
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| − | ***Any interference or damage to its nerve supply results in muscle atrophy
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| − | ****Can be rapid - over 50% of muscle mass may be lost in a few weeks e.g. roarer horses with [[Laryngeal Hemiplegia|laryngeal hemiplegia]]
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| − | ***May be reversible if innervation re-established
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| − | ***Histologically:
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| − | ****Fibres become rounded in cross section unless compressed by normal fibres
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| − | ****Increased concentration of nuclei as they take much longer to disintegrate
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| − | ****Fibrous stroma of epimysium and endomysium condenses -> more prominent
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| − | ****End result in muscle consisting of almost only fibrous tissue
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| − | ***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy''
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| − | ***Muscle may have a mixture of atrophied and [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophied]] (due to increased work load) fibres if some motor units are not damaged
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| − | **<u>'''Metabolisation of muscle protein'''</u> for nutrients during:
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| − | ***Malnutrition, cachexia, senility
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| − | ***Gradual onset except for some febrile diseases causing cachexia
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| − | ***Postural muscles are not affected, sometimes even [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophy]]
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| − | ***Histologically:
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| − | ****Some nuclei disappear as myofibre volume is decreased
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| − | ***Grossly:
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| − | ****Smaller, darker, thinner muscles
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| − | [[Category:Muscles - Degenerative Pathology]]
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