According to the Frank-Starling law of the heart: A. At lower end diastolic volu

Question

According to the Frank-Starling law of the heart:

A. At lower end diastolic volumes, stroke volume will increase due to more overlap of actin and myosin and more forceful contractions

B. If end diastolic volume increases, stroke volume will increase proportionately due to optimal overlap of actin and myosin

C. The shorter the initial length of the cardiac muscle fibers prior to contraction the more forceful will be the subsequent contraction

D. As cardiac output is reduced, blood pools in the veins so that arterial blood pressure increases and venous return increases

My choice is between B or D, not sure which one.

Explanation / Answer

According to Frank Starling law of the heart, B. If end diastolic volume increases, stroke volume will increase proportionately due to optimal overlap of actin and myosin.

Explanation: The stroke volume of the heart increases in response to an increase in the volume of blood filling the heart. The increase in the volume is referred to as end diastolic volume. When larger volume of blood flows, the blood streches the walls of the heart which causes greater diastolic expansion which in turn increases the force of contraction. This is due to increase in the load of each muscle fiber. This also causes increase in the calcium sensitivity along myofibrils, increasing cross bridges of actin and myosin. However, maximal force is rarely exceeded and the optimal overlap of actin and myosin is maintained which decreases the force of muscular contractions.

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