Myocardium Flashcards
What is the myocardium?
constitutes bulk of heart mass; externally lined by pericardium & internally by endocardium
How is myocardium similar to & different from skeletal muscle?
Myocardium has striations (sarcomeres) like skeletal muscle.
Unlike skeletal muscle, myocardial fibres are branched & join each other through intercalated disks.
What are abundant in myocardium & important for energy?
contain abundant mitochondria & myoglobin
What is the cell mb of cardiomyocytes called?
Sarcolemma
What is the cytoplasm of cardiomyocytes called?
sarcoplasm
What does the sarcoplasm contain?
Myofilaments which form bands (A, I, Z bands)
Each sarcomere goes from…
… 1 Z line to another
What is the myocardium’s capacity to regenerate?
unlike skeletal muscle, myocardium has practically no capacity to replace lost myofibers & therefore normal repair is impossible
What are cardiomyocytes particularly susceptible to? what else can cause injury?
Particularly susceptible to hypoxia & free radicals. Injury can also be caused by viruses, bacteria, cardiotoxins, or parasites
Degeneration & necrosis in cardiomyocytes?
microscopically, degeneration & necrosis are similar to that in skeletal muscle. myofibres undergoing degeneration swell, become hypereosinophilic, lose striations (dissolution of sarcoplasm & myofibrils), nuclear condensation, & eventually become fragmented
What is myocardial calcification/mineralization?
Calcium plays important role in normal physiology of heart. in many degenerative diseases this mineral cannot be removed from & becomes sequestered in sarcoplasm & organelles of myocardial cells.
How do excessive calcium deposits appear microscopically?
As dark-blue granules in sarcoplasm
Following necrosis, what happens to affected myocardial fibers?
They undergo cardiomyolysis & shortly after, macrophages & some neutrophils start cleaning up this myofiber debris
B/c cardiac muscle has practically no capacity to repair by regeneration, what happens?
Instead, necrotic tissue is replaces by CT (fibroblasts & collagen) which eventually results in cardiac fibrosis (scar)
Gross appearance of myocardial degeneration & necrosis?
pale discolouration of myocardium, wht scarring
What is ischemic myocardial necrosis?
Heart attack: plaque builds up in a place like the coronary artery, blood clot blocks artery blood flow.
Epidemiology of ischemic myocardial necrosis?
- v common in humans
- v rare in animals
Give 7 examples of causes of toxic myocardial necrosis
- Cardiac glycoside containing plants: Oleander
- other toxic plants: Phalaris, Lantana camara, Karwinskia humboldtiana (coyotillo), Cassia occidentalis, Vicia villosa (hairy vetch), Eupatorium rugosum (wht snakeroot), cottonseed meal (containing gossypol), avacado leaves (Persea americana)
- acute selenium toxicosis: ingestion of selenium-accumulating plants ex: locoweed (Astragalus & Oxytropis), Western Aster (Symphyotrichum ascendens)
- cantharidin due to ingestion of blister beetles (Epicauta spp)
- Doxorubicin (Adriamycin)
- Ionophores (Monensin, lasalocid, salinomycin)
- sodium fluoroacetate (compound 1080)
8 important facts of wht muscle disease
- mjr economic loss worldwide
- often manifests itself as sudden death
- affects farm animals, not Ca or Fe
- occurs mostly in rapidly growing animals
- for unknown reasons, sometimes WMD affects only skeletal muscle, or cardiac muscle, & sometimes both
- affects fetuses & causes abortion
- exacerbated by exercise or stress
- responds well to treatment, but only @ early stages of disease
Pathogenesis of wht muscle disease
- Cardiac & skeletal muscle cells utilize oxygen for normal physiology & as result oxygen radicals (free radicals) are normally & constantly generated in any healthy animal
- free radicals are highly toxic for cells but free-radical scavengers, ex: vit E & Selenium - containing enzyme glutathione peroxidase, neutralize these radicals & prevent cell injury
- deficiencies in Vit E & Se translate into reduced availability of free radical scavengers
- when free radicals overwhelm scavengers, excessive free radicals accumulate & cause peroxidation of cell mbs leading to cell degeneration
- degenerated cells are unable to pump out calcium & calcium accumulates in cells leading to mineralization
Gross lesions of wht muscle disease?
myocardial necrosis & calcification, wht discolouration of ventricular wall & septum, wht discolouration of skeletal musculature
Where in the heart does WMD affect?
for unknown reasons, WMD affects RV in lambs & LV in calves
What do you send when submitting tissues for histopathology for wht muscle disease?
send myocardium from both sides of heart
Appearance of wht muscle disease under microscope?
mineralized cardiomyocytes, and dark (blk) cells with von-kossa stain for calcium
What do Sw get instead of wht muscle disease?
Mulberry heart disease
What is mulberry heart disease in Sw from?
Vit E & Selenium deficiency
Gross signs of mulberry heart disease?
hemorrhage (petechia) & necrosis in myocardium, fibrin deposits attached to epicardium
Histo signs of mulberry heart disease?
hemorrhage & myocardial necrosis
What is neurogenic myocardial necrosis?
aka Brain-heart syndrome: trauma in brain or spinal cord sometimes can induce lesions in heart b/c of overstimulation of parasympathetic NS which will stimulate lrg release of catecholamines.