Cardiac Muscle Flashcards
Sliding filament mechanism
Actin filaments slide along w adjacent myosin filaments with cycling of CROSS-BRIDGES
Z lines come closer together
Cardiac muscle produces force/tension
Actin and myosin move away from each other - passive
2 principles of cardiac muscle
- cardiac muscle requires no nervous input
- if you stretch it more than normal there will be a stronger force of contraction
What underlies the ability of the heart to control stroke volume
Its ability to increase its contractile force with a slight increase in its length
if the muscle is overstretched, active tension decreases
What is preload
Stretched condition of the heart muscle at the end of diastole
What does an increased preload result in
Increased EDV, increased SV
Greater force of contraction =>
Greater stroke vol
Is blood left in the heart at the end of systole
YES so it doesn’t seize
What does every point on the starling curve have
THE SAME CONTRACTILITY (NOT the same as force of contraction)
What is contractility
SV for a given EDV - inherent ability of the heart to contract
Effect of sympathetic activity on starling curve
A higher starling curve => increased contractility
THEREFORE
a higher SV for the same EDV
What happens to ventricular pressure during the ISOVOLUMETRIC PHASE of systole
=> what is a good measure of contractility
VP rises (think - VP must rise above AP to open valve)
Max rate at which VP rises = dP/dt max - this is a GOOD MEASURE OF CONTRACTILITY
therefore
anything causing slope to rise increases contractility
What sort of agent causes an increase in contractility
+ve inotropic agent
What sort of agent causes a decrease in contractility
-ve inotropic agent
What is a powerful inotropic agent
Ca2+
What are positive inotropic agents
Noradrenaline Adrenaline increased Ca2+ influx and uptake by SR Increased EC Ca2+ SLOPE IS ALMOST VERTICAL
What are negative inotropic agents
hypoxia drugs Ca2+ channel blockers beta adrenergic blockers SLOPE IS ALMOST HORIZONTAL
What does Digoxin do
Increases IC Ca2+
Blocks Na+/K+ pump, slowing Na+-Ca2+ exchange
Where is the RYR density high
High near L-type Ca2+ channels
What facilitates CICR
Short distance between Ca2+ channels and RYR
What stops the release of Ca2+ from the SR
Inactivation of RYR by increased [Ca2+]
Local depletion of SR calcium
3 mechanisms for decreasing IC [Ca2+]
- SERCA
- Na+/Ca2+ exchange pump
- Cell membrane ATP-dependent Ca2+ pump
SERCA (70% in humans)
Regulated by phospholamban which inhibits Ca2+ uptake // SR
therefore Ca2+ pumps Ca2+ from cytoplasm into SR stores
Na+/Ca2+ exchange pump (most of remainder)
What is it powered by
Powered by Na+ GRADIENT
Cell membrane ATP-dependent Ca2+ pump
Small amount
