Myocardial Contractility Flashcards Preview

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Flashcards in Myocardial Contractility Deck (7)
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•the atria (or ventricles) acting as one large cell


intercalated discs

•the areas of contact between cells
•desmosomes (velcro)
•gap junctions (allow for sharing of onformation)


calcium ions

•their influx through slow calcium channels accounts for the prolonged plateau phase and absolute refractory period that enable cardiac muscle to function properly
•Ca++ ions also combine with the regulatory protein troponin in the troponin-tropomyosin complex - removes inhibition that prevents heads of myosin from forming cross bridges with the active sites on actin ***virtually identical to that of skeletal muscle mechanism
•approx. 20% of Ca++ required for contraction is supplied by the influx during the plateau phase, the rest is released from storage in the sarcoplasmic reticulum


calcium induced calcium release

•L-type channels in T tubules - voltage gated, respond to action potential, let a small amount of Ca++ in which triggers the opening of nearby Ca++ release channels in the lateral sacs of the sarcoplasmic reticulum
•in skeletal muscle, AP releases stored Ca++, modulate force by the number of fibers that get activated
•cardiac muscle modulates force by the amount of Ca++ released into the cytoplasm


positive inotropes

•sympathetic stimulation


negative inotropes

•parasympathetic stimulation
•calcium channel blockers


Law of Laplace

•wall tension is directly related to the product of the intraventricular pressure and internal radius and inversely related to wall thickness

T = P x R
•T = tension
•P = pressure
•R = lumen radius

o = T/h
•o = stress
•h = wall thickness