Myocardial Contractility Flashcards Preview

Cardio > Myocardial Contractility > Flashcards

Flashcards in Myocardial Contractility Deck (7)
Loading flashcards...
1

syncytium

•the atria (or ventricles) acting as one large cell

2

intercalated discs

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

3

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

4

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

5

positive inotropes

•sympathetic stimulation
•epinephrine
•dopamine
•isoproterenol
•hypercalcemia
•digoxin

6

negative inotropes

•parasympathetic stimulation
•hypoxia
•hyperkalemia
•propranolol
•calcium channel blockers

7

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