Force generation by heart Flashcards
what are myofibrils?
the contractile units of muscle, have alternating thick and thin segments
What is the thick and darker segment of myofibrils?
myosin
What is the thin and lighter segment of myofibrils?
actin
What structure is formed by the arrangement of actin and myosin?
sarcomeres = functional unit of muscle
How is muscle tension produced?
sliding of actin filaments on myosin filaments
muscle shortens and produces force
What is the release of calcium dependent on in cardiac muscle?
the presence of extra-cellular Ca2+
Where is calcium found during diastole? And what excitation-contracton events are happening?
Sarcoplasmic reticulum
contractile machinery relaxed
resting intracellular Ca2+ < extracellular Ca2+
What excitation-coupling events happen in plateau phase?
calcium enters myocytes
stimulates release of Ca2+ from SR (CICR)
now there is enough intracellular Ca2+ to stimulate contraction
What is the refractory period?
the period following an AP during which it is not possible to activate cardiac muscle
What is the purpose of the refractory period?
a long period prevents generation of tetanic contraction
Which channels are open/closed during refractory period?
K+ open during falling phase (efflux of K+)
Na+ channels shut since phase 2
SV = ?
End Diastolic Volume - End Systolic Volume
SV = EDV - ESV
What is the intrinsic control of SV?
changes in diastolic length of myocardial fibres
What determines the diastolic length of myocardial fibres?
the volume of blood within each ventricle at the end of diastole = EDV
What determines EDV?
venous return
What does the Frank-Starling curve describe?
the relationship between venous return, EDV and SV
What is Starling’s Law?
the more the ventricle is filled with blood during diastole (EDV), the greater the volume of ejected blood will be during the resulting systolic contraction (ESV)
Stretch has what effect on the affinity of troponin for Ca2+?
increases affinity of troponin for calcium
When skeletal muscle is contracted, it is at its optimum length.
True/False?
False
Optimal fibre length of skeletal muscle is at resting muscle length.
How is optimal muscle length of cardiac muscle achieved?
stretching the muscle achieves optimum length
According to Starling’s Law, what happened if venous return to the right atrium increases?
the EDV for the RA would increase
increasing SV to the pulmonary artery
What happens when SV decreases - according to Starling’s Law?
force of contraction increases to compensate - this is possible since larger EDV remains in ventricles - stretches muscles -> optimum length
What controls SV extrinsically?
hormones and nerves
Which nervous system supplies the ventricles: sympathetic or parasympathetics?
sympathetics
How does sympathetic stimulation control SV?
stimulation increases force and rate of contraction
A positive chronotropic effect is seen when what happens?
increase rate of contraction
A negative inotropic effect is seen when what happens?
decrease in force of contraction
Which way does sympathetic stimulation shift the Frank-Starling curve?
to the left
Which hormones are involved in the extrinsic control of SV?
adrenaline
noradrenaline
What is the effect of adrenaline binding to alpha receptors?
vasoconstriction
skin, gut, kidney, arterioles
What is the effect of adrenaline binding to b2-receptors?
vasodilation
cardiac and skeletal muscle arterioles
