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===Response to injury===
|backcolour =CDE472
|linkpage =Musculoskeletal System - Pathology
*Limited array of ways in which to respond to injury
**[[:Category:Muscles - Degenerative Pathology|Degeneration]]
|maplink = Musculoskeletal System (Content Map) - Pathology
**[[Muscle Necrosis|Necrosis]]
|pagetype =Pathology
**Regeneration
|sublink1=Muscles - Pathology
**[[Muscle Atrophy|Atrophy]]
**[[Muscle Hypertrophy|Hypertrophy]]
*Large number of factors indicing the changes above, e.g.:
**Trauma
**Toxins
**Infectious agents
**Nutritional deficiencies
**Ichaemia
**[[:Category:Muscles - Developmental Pathology|Hereditary diseases]]
*Specific diagnosis is often not possible based on morphological or histological features alone
*Additional tests, clinical information and history are often required
===Regeneration===
[[Image:Muscle regeneration.jpg|right|thumb|100px|<small><center>Muscle regeneration (Image sourced from Bristol Biomed Image Archive with permission)</center></small>]]
*Skeletal muscle myofibres have substantial regenerative ability
*Success depends on:
**An intact '''sarcolemmal tube''' - to act as a support and guide
**Availability of '''satellite cells''' - to act as progenitor cells for new sarcoplasm production
**Macrophages to clear up cell debris
**If these conditions are not met (e.g. severe thermal damage) '''fibrosis''' will occur
*Stages:
#Nuclei in [[Muscle Necrosis|necrotic segement]] disappear, hyalinased sarcoplasm due to loss of normal myofibrillar structure, may separate from adjacent normal myofibrils and/or [[Muscle Calcification|mineralise]]
#Monocytes from capillaries -> macrophages in necrotic portion, satellite cells swell -> vesicular with prominent nucleoli -> mitosis (within 1-4 days after initial injury)
#Satellite cells move to centre
#Macrophages clear the sacrolemmal tube, plasmalemma disappears, shape maintained by basal lamina
#Satellite cells -> myoblasts (contain myosin) -> fuse forming myotubes with row of central nuclei; cytoplasmic processes fusing
#Growing and differentiating fibre, striations appear - formation of sarcomeres
#Nuclei move to peripheral position (2-3 weeks after initial injury)
*Regeneration by '''budding'''
**When conditions are not optimal, disrupted sacrolemma
**E.g. injection of irritating substance, trauma, [[Muscle Ischaemia|infarction]]
**Myoblasts proliferate -> sacrolamma bulges from cut part -> club-shaped with numerous central nuclei = muscle giant cells
*Monophasic lesions - all at same phase above
[[Category:Muscles - Pathology]]