Tissue Processing/ Pathology of Skeletal Muscle Pt 1 Flashcards
What is the processing criteria for histological specimens to be used?
- Must be well preserved: fixation in 10% formalin
- Be sufficiently thin - Cut by microtome (sections 1-7 micro)
- Have contrast
What is tissue sections embedded in when cut with the microtome?
Paraffin
What part of skeletal muscle is circled in blue?
Perimysium
What part of skeletal muscle is circled in red?
Epimysium
What part of skeletal muscle is represented in purple?
Endomysium
What is the structural/ functional unit of skeletal muscle?
Sarcomere
What is the position of the nucleus in the cardiac muscle? What skeletal muscle?
Cardiac Muscle: central Nuclei
Skeletal Muscle: Nuclei in periphery
How can you prevent contraction of the muscle tissue when it is in contact with fixative?
Place the sample on a tongue depressor, and secure it with 2 (26 g needles).
What are type I muscle fibers?
Red, slow twitch and slow fatiguing – rich in
mitochondria (energy from oxidative phosphorylation); they rely mainly on the oxidative metabolism of fats for their energy supply.
What are Type II muscle fibers?
White, fast twitch. Energy from glycolysis. They
have fewer mitochondria and myoglobin than type I fibres (short bursts of athletic activity)
What does type of stain, stains Type I muscle fibers?
Stain strongly with stains for succinate dehydrogenase (SDH) and lightly with the myosin-ATPase reaction (e.g.: diaphragm).
What type of stain, stains Type II muscle fiber darkly
Stains darkly with the NADH reaction.
Which is the darker stained type of muscle in this ATPase Reaction? The lighter muscle?
Type II - Darker
Type I - Lighter
What post mortem changes can be seen for muscle?
- Pallor ( pale discoloration of muscle)
- Dark- red discoloration: Could be the result of rhabdomyolysis, or putrefaction.
- Rigor Mortis.
What is rigor mortis? How long does it take for rigor mortis to occur after death? What can affect the timeframe? What happens after the patient is in rigor?
- Stiffening of muscles and joints after death.
- The rapidity/ onset depends on many factors such as environmental/ internal temperature, muscle ph, and glycogen reserves in muscle at time of death. On average begins 2-4 hours after death and reaches maximum at 24 hours, then disappears gradually in same order as it started.
What is the progression of rigor mortis?
Starts in jaws and trunk, then progresses to limbs.
What are the growth disturbances?
Atrophy, Hypertrophy, hyperplasia
What are the skeletal muscle reactions to injury?
Degeneration/ Necrosis/ Calcification/ Regeneration
What are the skeletal muscle congenital/ inherited defects?
Arthrogryposis, Muscle dystrophy, PSM, PSS
What are exertional myopathies of skeletal muscle?
Azoturia, HYPP, Canine rhabdomyolysis, capture myopathy, compartment syndrome.
What are the traumatic myopathies?
Downer syndrome, post anesthetic myopathy, crush syndrome ( acute trauma)
What are the types of inflammatory pathology of muscles?
Bacterial: Malignant edema; black leg
Parasitic Myositis Trichinosis; Cysticercosis; Sarcocystosis; Toxoplasmosis
Idiopathic: Canine Masticatory Myositis; Canine Dermatomyositis
What are the primary neoplasia pathology of muscle?
Primary Neoplasia: Rhabdomyoma; Rhabdomyosarcoma
What are the three types of atrophy? What are their characteristics?
- Denervation (neurogenic) atrophy: Characterized by rapid atrophy (half muscle mass in weeks).
• Disuse atrophy: Innervation is intact (tonic stimuli). Atrophy
is associated to immobilization of a limb or body part
because of pain (fracture, tenotomy, ankylosis etc).
• Atrophy of cachexia/ malnutrition: Occurs slowly over time.
What can occur with long standing denervation atrophy?
Long standing denervation may result in fibrosis and fat infiltration (steatosis) of affected muscles.
What type of muscle fibers are typically affected with Atrophy of cachexia?
Type II (white, fast twitch) fibers are primarily affected.
What is occuring in this image? What kind of atrophy is being seen here?
Horse with laryngeal hemiplegia – idiopathic degeneration of the left recurrent laryngeal nerve: “Roarer horse”. Left crico-arytenoideus dorsalis muscle atrophy. AVC
NEUROGENIC (Denervation) atrophy
What is hypertrophy? What can enhance it?
It is the muscle response to increased work load (physiologic/ compensatory hypertrophy). There is an increase in the size but not in the number of muscle fibers. Can be enhanced by steroidal drugs.
What is occuring in this image? How can you tell?
Hypertrophy. Increase in muscle size, not in quantity of muscle tissue
What is muscular hyperplasia? Who does it occur in?
Hyperplasia: Muscular hyperplasia occurs in beef cattle (Charolais, Santa Gertrudis, Angus, Belgian Blue, etc.) with an inherited defect in the myostatin gene that normally limits muscle growth -> “double muscling” . There is an increased in the number of muscle fibers which are of normal size and structure,
Where is the gene defect that causes double muscling? What areas of the body are primarily affected? What are they at risk for?
- inherited defect in the myostatin gene
- Muscles of the thighs, rump, loin, and shoulder are primarily affected giving these animals a very athletic appearance.
- Dystocia may occur.
What is the pathology seen in this dog? What is she at risk for?
Hyperplasia - Double muscling
She is at risk for dystocia.
What are the reactions to muscle injury that can be seen? Can it be reversible?
Degeneration/ Necrosis/ repair.
Can be reversible (if there is preservation of the basal
lamina and the satellite cells).
In severe injury, necrosis will follow.
Where does degeneration/ necrosis occur in muscle tissue after injury?
Often occurs segmentally along the length of the
myofiber.
What is the gross pathology of a muscle with a severe case of an degenerative lesion/ necrotic lesion?
Muscles become pale and occasionally calcified; red discoloration may occur in cases in which there is hemorrhage or rhabdomyolysis (release of myoglobin in the interstitium.
What can be seen in this image? What are the dark pink circles representative of?
Hypercontraction of muscle fibers large rounded eosinophilic fibers, Early stages of muscle fiber degeneration/ necrosis.
What is the microscopic characterization of myofiber degeneration?
Microscopically myofiber degeneration is characterized by swelling, hyalinization, loss of striations and fragmentation.
Finish this sentence: Calcification, in severe cases starts as _____ ______ _______ and can be detected grossly. What can be seen in the muscle tissue with this pathology?
Calcification, in severe cases starts as mitochondrial calcium overload and can be detected grossly.
white, chalky gritty foci scattered throughout the affected
muscle.
What is the differece between muscle injury that is non disruptive and disruptive? What will occur as a result?
- If the injury is non-disruptive the basement membrane (basal lamina) will remain intact and will provide the framework for effective repair.
• If the injury is disruptive, as may occur with severe trauma (e.g., laceration, tearing), then repair will not be as efficient, and scarring will occur (part of the damage muscle will be replaced by fibrous connective tissue).
How long does it take for myofiber regeneration? What may persist after this period
Myofiber regeneration is completed in 2-3 weeks although central nuclei and nuclear rowing may persist beyond this time.
What occurs on a cellular level with a non disruptive muscle injury?
- Satalite cells proliferate and migrate to damaged myofiber
- They become myoblasts which fuse to form multinucleated cellular bands.
What is occuring in the circled area?
Nuclear rowing: Evidence of myofiber regeneration.
Is the presence of segmental necrosis and regeneration helpful in determining the cause? What is helpful?
Their presence alone are not helpful in determining the cause.
• Assessing the distribution and the duration of the lesions, however, has proven useful in determining the possible causes of muscle degeneration/necrosis.
What is a monophasic lesion? A polyphasic? What does this help indicate?
The concept of whether the lesion is monophasic (same duration, indicative of a single insult) or polyphasic (different stages of development, indicative of an ongoing degenerative process), has further improved the diagnostic evaluation of muscle injury.
What is an example of a monophasic injury? A multifocal monophasic injury? A polyphasic mucle injury?
- A focal monophasic injury would be the result of a single incident, e.g., IM injection.
- Examples of multifocal monophasic injury: a single episode of strenuous exercise
(exertional myopathy) or a single exposure to a muscle toxin like monensin.
-Example of polyphasic muscle injury are nutritional myopathy (Vit E/ selenium deficiency) and muscular dystrophy -> ongoing insult so both degeneration/necrosis and regeneration will be observed at any given time in the affected muscle.
What is Rhabdomyolysis? What is the pathology of muscle tissue affected?
Rupture of muscle fibers, can result in dark red discoloration of muscle tissue.
Why does NADH stain type II muscle fibers darker than type 2 mucle fibers?
This is because type 2 muscle fibers contain more mitocondria which is the reason that NADH stains it more intensely.
