Skeletal muscle
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Transcript of Skeletal muscle
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E. Simko WCVM
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Reading material:
E. Simko WCVM
1. Review the normal structure and function of skeletal muscle (in your notes or general textbooks)
2. McGavin M.D. 1995, Muscle, Chapter 9 in Thomson's Special Veterinary Pathology, Carlton W.W. et al, pp 461 - 498
NB - Put special emphasis on the topics covered during the lectures.
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Define following conditions and give examples:• Denervation atrophy• Disuse atrophy• Malnutrition atrophy• Muscular hypertrophy• Ischemic myopathy
- Occlusion of the vascular system- External pressure on a muscle- Swelling of a muscle in a non-expandable compartment
Objectives for Muscle dz:
E. Simko WCVM
Describe mechanisms of:• Muscular regeneration• Muscular repair
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Objectives for Muscle dz:
E. Simko WCVM
You should be able to define, describe pathogenesis, list lesions and know how to diagnose the following conditions/diseases:
• Nutritional myopathy (White muscle disease)• Toxic myopathy (Monensin toxicity)• Exertional myopathy• Gas gangrene and malignant edema• Blackleg• Botulism• Tetanus• Myasthenia gravis• Masticatory muscle myositis
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• Complex biochemistry and physiology• Simple pathology• Very long multinucleated cells• Segmental necrosis• Unique regeneration
Unique features
E. Simko WCVM
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Muscle (epimysium)
Muscle bundle (perimysium)
Myocyte (endomysium)
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Satellite cell
Basal lamina
Plasmalemma
Nucleus
Myofibril
Mitochondria
Myosin Actin
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Endomysium
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Type II fibers (white) • Fast movement• Glycolytic• Fast contracting • Fast fatiguing
Type I fibers (red) • Postural• Oxidative• Slow contracting• Slow fatiguing
E. Simko WCVM
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Contractile mechanism (Histology & physiology notes)
Rigor mortis (Thomson's Special Veterinary Pathology p. 396)
E. Simko WCVM
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Response to injury - Atrophy
• Atrophy• Hypertrophy• Degeneration / Necrosis• Inflammation
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Suprascapular nerve paralysis (sweeney)Radial nerve paralysis in dogs
Response to injury - Atrophy
• Denervation
• Disuse
• Malnutrition
FractureRecumbency
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E. Simko WCVM
Work hypertrophy
Compensatory hypertrophy
Response to injury - Hypertrophy
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Response to injury
Myocyte necrosis Cell membrane disintegrationLeakage of cytosol substances (creatine kinase (CK), myoglobin)
Indicators of muscle damage.
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Regeneration Repair
Both function & structure are re-established COMPLETELY
Function & structureare re-established
ONLY PARTIALLY(due to fibrosis)
Tissue injuryloss of functionand structure
E. Simko WCVM
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Regeneration and repair
E. Simko WCVM
• Debridement
• Tissue scaffold
• Germinal cells
• Blood supply
Prerequisites for regeneration:
If any of these is missing
Repair(scarring)
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Regeneration and repair
E. Simko WCVM
Satellite cell
Basal lamina
BLOOD SUPPLY
SCAFFOLD
GERMINAL CELLS
DEBRIDEMENT
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See regeneration described in Thomson’s Spec. Path on page 467 and 468, Figure 9-5.
Regeneration and repair - regeneration
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E. Simko WCVM
Regeneration
Regeneration and repair - Regeneration
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E. Simko WCVM
Regeneration and repair - Regeneration
Regeneration
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E. Simko WCVM
Regeneration and repair - Regeneration
Regeneration
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Regeneration and repair - Repair
E. Simko WCVM
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E. Simko WCVM
Regeneration and repair - Repair
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E. Simko WCVM
Regeneration and repair - Repair
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E. Simko WCVM
Response to injury - Necrosis
Vascular occlusion
External pressure on muscle
Muscle swelling in non-expandable compartment
Saddle thromboembolus (Fe, Eq)Equine Purpura Hemorrhagica
Pressure in muscle exceeds perfusion pressure in capillaries
Prolonged recumbencyToo-tight plaster casts
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E. Simko WCVM
Response to injury - Necrosis
(White muscle dz)
• Vit E and/or Se deficiency
• Economically important muscle dzin Bo, Ov, Cap, Po and Eq
Ruminants: skeletal muscles and heart
Pigs: liver (hepatosis diatetica) heart (mulberry
heart disease)
• Lesions: opaque, white muscle (mineralization)
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E. Simko WCVM
Response to injury - Necrosis
Necrosis
Loss of protection against free radicals
Peroxidation of membrane lipids
Disturbance of membrane permeability
Influx of calcium into cytosol
Accumulation of calcium in mitochondria
Damaged mitochondria
Energy exhaustion
Vit E and/or Se deficiency
Pathogenesis
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E. Simko WCVM
Response to injury - Necrosis
Diagnosis
Histology
Se and Vit E levels in the liver, feed
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E. Simko WCVM
Response to injury - Necrosis
• Feed additive overdose
• Lesions: necrosis (ill-defined, pale streaks) in myocardium and skeletal muscles
• Pathogenesis:
Interferes with ion transmembrane transport
Calcium influx and mitochondiral damage
Energy exhaustion
Necrosis
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E. Simko WCVM
Response to injury - Necrosis
Diagnosis
Histology
Monensin levels in feed and stomach content
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E. Simko WCVM
Response to injury - Necrosis
Excessive muscle activity
Sudden production of heat and lactic acid & ???
Coagulation of contractile proteins
Muscle swelling and decrease blood perfusion
Ischemia and necrosis
* Often with myoglobinuria
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E. Simko WCVM
Response to injury - Necrosis
Equine Rhabdomyolysis (muscle necrosis)Azoturia (Monday morning diseaseTying-up (Transient exertional rhabdomyolysis)
Capture myopathy (wildlife)
Lesions: necrosis of the major muscles
Diagnosis: HistoryMyoglobinuriaMuscle necrosis
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E. Simko WCVM
Response to injury - Inflammation
Lesions: Dry, red-black, porous necrotic musclesSerohemorrhagic exudation
DiagnosisDemonstration of Clostridial agentsPresence of the characteristic lesions
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E. Simko WCVM
Response to injury - Inflammation
Gas gangrene and malignant edema
Bo, Eq, Ov, Cap, PoPenetrating wounds infected by C. septicum,
C. perfringens, C. novyi, and C. chauvoei
Blackleg (Bo, Cap, Ov)Activation of spores of C. chauvoei disseminated from the GI tract to muscles
* Clostridial requirements for low O2
* Death is due to toxemia and septicemia.
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Response to injury - Inflammation
E. Simko WCVM
• Systemic or local infectionsBacterialViralParasitic
Dz associated with clostridial toxins:TetanusBotulism
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E. Simko WCVM
Response to injury - Inflammation
Masticatory Muscle MyositisEosinophilic myositis - acute formAtrophic myositis - chronic form
• Lesions: Acute - extremely swollen, hard, painful, musclesChronic - marked atrophy
• Autoantibodies against type IIM fibers
• Diagnosis:Muscle biopsySerology for autoantibodies
Polymyositis
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Congenital & hereditary disorders
Muscle weakness and fatigue exacerbated by exercise and resolves with rest (in dogs and occ. in cats and goats
Autoimmune dz - Ab against acetylcholine receptorsAdult dogs with megaesophagus, aspiration pneumonia
Inherited autosomal recessive deficiency in AchRs
• Acquired
• Congenital
• DiagnosisCholinesterase inhibitors, Demonstration of Ab,
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Rhabdomyosarcoma
Primary
Secondary
Rhabdomyoma