Muscle (AH) Flashcards
Crossed with class notes, TQs and Muzzy review.
Type I mm fibers
redslow twitchsmallmore mitochondriano glycogen
Type II mm fibers
White fast twitchlarge less mitochondria more involved in atrophy II A = oxitative + glycolytic. II B = glycolytic.
***What is the process that leads to Rigor Mortis?
decreased O2 –> decreased ATP –> decreased Ca2+ ATPase pump activity –> decreased Ca removal –> sustained contraction.
How does Rigor Mortis progress?
Start - 2hrs
Max - 24-48 hrs
Dissipates - 72 hrs.
Starts at jaw and trunk and then goes to extremities.
In what breeds of cattle is muscular hyperplasia hereditary? *Why does it happen?
Charolais and Belgian Blue. Mutation of myostatin gene –> double muscling
What spp. gets myofibrillar hypoplasia?
Pigs
Etiology of myofibrillar hypoplasia?( 3)
- Hereditary - decreased number of myofibrils in muscle fibers.
- Teratogenic - Toxins (F. graminearum = F-2 toxin = mycotoxicosis) –> depressed growth in utero.
- Choline or methionine deficiency –> decreased Ach synthesis and energy production.
Pathogenesis of Polysaccharide storage myopathy in horses?
Carbohydrate metabolic disorder –> insufficient energy production –> decrease in mm. –> Acute myoglobinuric nephrosis (pigment nephrosis)
Etiology of Glycogenoses (glycogen storage Dz)?
Missing or defective enzyme (inherited) –> accumulation of glycogen
What is Myotonia?
Channelopathy. Inability of myofibers to relax resulting in spasmodic contractions.
Etiology of HYPP?
Genetic mutation of skeletal mm sodium channel gene –> delayed inactivation of sodium channel activity –> uncontrolled twitching and hyperkalemia in bloodstream.
HYPP sequelae?
Laryngeal mm dysfunction. Trembling, weakness, collapse. Metabolic acidosis –> cardiotoxicity and pumonary edema. Can be fatal.
What is Arthrogyposis?
Muscle hypoplasia due to lack of muscle innervation during gestation.
Lesions of Arthrogyposis?
Atrophy and dysplasia of muscles Fibrosis → Curvature and rigidity of joints = Crooked limbsPossibly born dead
Etiology of Arthrogyposis?
Infectious:
- viral (BVD, Akabane)
- vaccinations druing 1st trimester (ruminants) for Rift Vally fever, wesselbron virus, bluetongue. Non-infectious:
- inherited in suffolk lambs
- Plant poisoning (lupinus spp.) causes decreased movement in utero
What is the primary defect associated with Arthrogyposis?
Always associated with spinal and brain abnormalities.
What is mm atrophy?
Decrease in size of cells that have gained full development
Mm atrophy etiology?
- Diminished level of work
2. Removal of source of nutrition or stimulation (more common)
What are the types of mm atrophy?
Denervation - lack of tonic stimuli.
Disuse - decrease of tonic stimuli.
Malnutrition and cacexia - small, thin, dark mm.
Senile- similar to malnutrition + lipofuscin.
Pressure
Which type of atrophy effects both type I and II fibers. What about the others?
Denervation = I and II fibers.
The rest = only type II.
Give three examples of denervation atrophy syndromes
- Equine lyaryngeal hemiplegia (roaring).
- Damage to suprascapular nerve in horses (sweeny).
- Radial or brachial paralysis in dogs associated with trauma.
Lesions of denervaiton atrophy?
Diffuse atrophy involving BOTH type I and II fibers
Lesions of Disuse atrophy?
Mainly involves Type II fibers.
Flabby shrunken muscles.
What is the most common form of Atrophy?
Atrophy of malnutrition and cachexia.
Etiology of atrophy of malnutrition and cachexia? (5)
Malnutrition, Starvation, Severe helminthosis, Chronic debilitating diseases (TB, Johne’s Dx), Neoplasia
Lesions of atrophy of malnutrition an cachexia?
type II fibers involved.
Small, thin, dark, sticky, flabby mm.
Lesions of senile atrophy?
Lipofuscin –> yellow brown color, especially in diaphram.
What causes pressure atrophy?
Prolonged pressure of muscles from abscesses, tumors, parasitic cysts
What is Hypertrophy?
Incease in size of mm by an increase in fiber size. No new cells, just bigger size.
Etiology of hypertrophy?
- physiologic - athletic training, pregnant uterus.
- Pathologic (left cardiac ventricular hypertrophy.)
- Idiopathic (esophagus, ileum - horses).
- Iatrogenic - steroids.
Lesions of hypertrophy?
Dark red. Increase in myofiber diameter. Increased myoglobin. Larger cellular organelles.
What is steatosis?
Defective myofiber development –> replacement of muscle tissue by adipose tissue.
How do mm affected by severe steatosis appear?
Soapy, marbling appearance. Not clinically significant.
What is muscular dystrophy?
Progressive degeneration due to abnormal muscle proteins (ex: dystrophin).
Etiology of muscular dystrophy? (2)
- Idiopathic: Primary defect in myofiber itself w/ inadequacy of regen activity (innervation is sound)
- Hereditary- Marino sheep, Canine X-linked mm dystrophy, HMLR
General lesions of muscular dystrophy?
Failed attempts to regenerate –> Fibrosis.
Clinical presentation of HMLR?
In young dogs. Bunny hopping. +/-megaesophagus –> aspiration pneumonia.
What is the defect in dogs with Canine X-linked mm dystrophy?
Dystrophin deficiency. Duchenne type
What specific condition is associated with mm rupture?
Fibotic and ossifying myopathy (torn hamstring in quarter horses).
Sequelae of ruptured mm.?
Diaphragmatic rupture or rent–> eventration. In racing greyhounds –> muscle ruptrue during strenuous activity.Tearing from slipping cows
Lesions of congestion?
swollen, red to black.
What is an example of mm congestion?
Bovine ruminal tympany (bloat)
Lesions associated with bloat?
Cervical esophagus is red.
Thoracic esophagus is pale (white).
Extensive congestion of cervical region extending to the head. ==> bloat line.
Thrombosis, Embolism, and infarction lesions?
hemorrhage and necrosis in infarcted muscle, thrombus
What are the three responses of mm to injury?
degeneration, necrosis, regeneration
What is true about etiology of degeneration/necrosis?
There is a stereotyped response making it hard to determine etiology.
Histopathological interpretation of degeneration/necrosis
Monofocal monophasic - local trauma.
Monofocal multiphasic - repeated local trauma.
Multifocal monophasic - single exposure to mycotoxins or metabolic disorders.
Multifocal, multiphasic - nutritional deficiency or muscular dystrophy.
Gross lesions of mm degeneration?
Degenerated mm. appear pale.
- Chalky/white = severe calcification.
- Red = hemorrhage/ rhabdomyolysis (myoglobin release)**
- Chalky/white = severe calcification.
Micro lesions of mm degeneration? (6)
Vacuoles and loss of striations followed by swelling, hypereosinophilia, glassy or hyaline appearance (Zenker’s necrosis)
Finally, segmental rupture of fibers and formation of retraction caps
When is mm degeneration irreversible?
once necrosis ensues
Ddx for degeneration?
gross lesion = pallor.
Muscle pallor can also indicate pale muscles of veal calves, enemia, exsanguination, fat.
What are the mechanisms of cell injury that lead to necrosis?
- Ischemic and hypoxic injury –> ATP depletion.
- Generation of reduced oxygen species –> Free radical injury .
- Defects in membrane permeability –> membrane damage.
- Disruption of calcium homeostasis –> calcium influx –> mitochondrial damag
Gross/Micro lesions of necrosis?
Gross: pallor, dry gritty.
Micro: swollen, hypereosinophilic, fragmented sarcoplasm, persistent basal lamina, magrophage invasion, regeneration or fibrosis.
What are the main categories of degenerative myopathies?
Nutritional, Exertional, Toxic, Electrolyte, Stress, Ischemic, Endocrine, (Muscular Dystrophy)
TQ What is the pathogenesis of nutritional myopathies?
Decrease in Se / Vit E–> –> Lipid peroxidation –> damage to CM –> Ca2+ influx –> Mitochondrial damage –> segmental necrosis