PHYS Contraction of Cardiac Muscle

Question 1

Process of cardiac muscle excitation.

Answer 1

During excitation, Ca2+ enters cardiomyocytes via L -type Ca2+ channels (voltage-gated) which then triggers ryanodine receptors to release intracellular Ca2+ from sarcoplasmic reticulum (site of intracellular Ca2+ stores).

Question 2

Formulae for CO

Answer 2

CO = HR x SV
(L/min)

Question 3

CO

Answer 3

Volume of blood pumped by each ventricle of the heart/min.

Question 4

Diastole

Answer 4

Period when ventricles fill will blood.

Question 5

Systole

Answer 5

Period when ventricles contract & eject blood into the arteries.

Question 6

SV

Answer 6

Volume of blood ejected w each ventricular contraction = EDV - ESV (End Diastole - End Systolic Volume)
(ml/beat).

Question 7

What is SV proportional to?

Answer 7

Ventricular end-diastolic volume (ml)

Question 8

Explain Frank-Starling mechanism re relationship btw myocardial stretch & SV.

Answer 8

Increase EDV, increases ventricular pressure, ventricular muscle cell stretch, increase sarcomere length, increased cross bridge formation, increased force of contraction.

Question 9

How can SV & CO be increased during exercise?

Answer 9

Changing cardiac muscle length & altering Ca2+ availability.