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Cardio > Force generation by heart > Flashcards

Force generation by heart Flashcards

1
Q

what are myofibrils?

A

the contractile units of muscle, have alternating thick and thin segments

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2
Q

What is the thick and darker segment of myofibrils?

A

myosin

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3
Q

What is the thin and lighter segment of myofibrils?

A

actin

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4
Q

What structure is formed by the arrangement of actin and myosin?

A

sarcomeres = functional unit of muscle

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5
Q

How is muscle tension produced?

A

sliding of actin filaments on myosin filaments

muscle shortens and produces force

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6
Q

What is the release of calcium dependent on in cardiac muscle?

A

the presence of extra-cellular Ca2+

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7
Q

Where is calcium found during diastole? And what excitation-contracton events are happening?

A

Sarcoplasmic reticulum
contractile machinery relaxed
resting intracellular Ca2+ < extracellular Ca2+

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8
Q

What excitation-coupling events happen in plateau phase?

A

calcium enters myocytes
stimulates release of Ca2+ from SR (CICR)
now there is enough intracellular Ca2+ to stimulate contraction

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9
Q

What is the refractory period?

A

the period following an AP during which it is not possible to activate cardiac muscle

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10
Q

What is the purpose of the refractory period?

A

a long period prevents generation of tetanic contraction

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11
Q

Which channels are open/closed during refractory period?

A

K+ open during falling phase (efflux of K+)

Na+ channels shut since phase 2

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12
Q

SV = ?

A

End Diastolic Volume - End Systolic Volume

SV = EDV - ESV

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13
Q

What is the intrinsic control of SV?

A

changes in diastolic length of myocardial fibres

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14
Q

What determines the diastolic length of myocardial fibres?

A

the volume of blood within each ventricle at the end of diastole = EDV

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15
Q

What determines EDV?

A

venous return

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16
Q

What does the Frank-Starling curve describe?

A

the relationship between venous return, EDV and SV

17
Q

What is Starling’s Law?

A

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)

18
Q

Stretch has what effect on the affinity of troponin for Ca2+?

A

increases affinity of troponin for calcium

19
Q

When skeletal muscle is contracted, it is at its optimum length.
True/False?

A

False

Optimal fibre length of skeletal muscle is at resting muscle length.

20
Q

How is optimal muscle length of cardiac muscle achieved?

A

stretching the muscle achieves optimum length

21
Q

According to Starling’s Law, what happened if venous return to the right atrium increases?

A

the EDV for the RA would increase

increasing SV to the pulmonary artery

22
Q

What happens when SV decreases - according to Starling’s Law?

A

force of contraction increases to compensate - this is possible since larger EDV remains in ventricles - stretches muscles -> optimum length

23
Q

What controls SV extrinsically?

A

hormones and nerves

24
Q

Which nervous system supplies the ventricles: sympathetic or parasympathetics?

A

sympathetics

25
Q

How does sympathetic stimulation control SV?

A

stimulation increases force and rate of contraction

26
Q

A positive chronotropic effect is seen when what happens?

A

increase rate of contraction

27
Q

A negative inotropic effect is seen when what happens?

A

decrease in force of contraction

28
Q

Which way does sympathetic stimulation shift the Frank-Starling curve?

A

to the left

29
Q

Which hormones are involved in the extrinsic control of SV?

A

adrenaline

noradrenaline

30
Q

What is the effect of adrenaline binding to alpha receptors?

A

vasoconstriction

skin, gut, kidney, arterioles

31
Q

What is the effect of adrenaline binding to b2-receptors?

A

vasodilation

cardiac and skeletal muscle arterioles

Cardio (15 decks)

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