Difference between revisions of "Muscle Atrophy"

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****End result in muscle consisting of almost only fibrous tissue  
 
****End result in muscle consisting of almost only fibrous tissue  
 
***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy''
 
***Sometimes replaced by fat tissue -> increased size of muscle = ''pseudohypertrophy''
***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
+
***Muscle may have a mixture of atrophied and [[Muscle Hypertrophy|hypertrophied]] (due to increased work load) fibres if some motor units are not damaged
 
**<u>'''Metabolisation of muscle protein'''</u> for nutrients during:
 
**<u>'''Metabolisation of muscle protein'''</u> for nutrients during:
 
***Malnutrition, cachexia, senility
 
***Malnutrition, cachexia, senility
 
***Gradual onset except for some febrile diseases causing cachexia
 
***Gradual onset except for some febrile diseases causing cachexia
***Postural muscles are not affected, sometimes even [[Muscles Hyperplastic and Neoplastic - Pathology#Hypertrophy|hypertrophy]]
+
***Postural muscles are not affected, sometimes even [[Muscle Hypertrophy|hypertrophy]]
 
***Histologically:
 
***Histologically:
 
****Some nuclei disappear as myofibre volume is decreased
 
****Some nuclei disappear as myofibre volume is decreased

Revision as of 11:42, 7 March 2011

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