More than one choice may be correct. Select all correct choices.

Frank-Starling Law of the Heart states that, within limits, stretching of the walls of the ventricle before contraction will result in ____ at the next beat.

Question

More than one choice may be correct.  Select all correct choices.

Frank-Starling Law of the Heart states that, within limits, stretching of the walls of the ventricle before contraction will result in ____ at the next beat.

BlackTom AI · Accepted Answer

1) Relevant knowledge points and concepts:
Frank–Starling law (the Starling mechanism) describes an intrinsic property of cardiac muscle: within physiological limits, increased ventricular filling (end-diastolic volume/preload) stretches myocardial sarcomeres, producing a greater active tension on the subsequent contraction. Mechanistically this involves the length–tension relationship of cardiac muscle and increased sensitivity of contractile proteins to Ca2+ at longer sarcomere lengths. The result is an increased stroke volume, matching output to venous return.

2) Step-by-step reasoning:
- Increased venous return raises end-diastolic volume (EDV).
- Higher EDV causes greater stretch of ventricular muscle fibers (longer sarcomere length).
- At these longer lengths, actin–myosin overlap and regulatory protein behavior produce greater force generation for a given Ca2+ transient (length–tension relationship + increased Ca2+ sensitivity).
- Greater force of contraction during systole ejects more blood from the ventricle.
- Hence stroke volume increases on the next beat, up to a physiological limit.

3) Intermediate/calculation steps:
No numerical calculation is required here. Conceptually: EDV ↑ → preload ↑ → fiber stretch ↑ → force of contraction ↑ → stroke volume (SV) ↑. The relation is monotonic within normal ranges; if EDV exceeds optimal sarcomere length, force falls.

4) Why the correct answers are correct:
"Greater force of contraction of the muscle fibers" is the direct cellular consequence of increased preload (stretch). "A greater stroke volume" is the organ-level consequence because the stronger contraction ejects more blood. Both follow directly from the Frank–Starling mechanism.

5) Why other options are incorrect (common distractors):
- Increased heart rate is not a direct result of ventricular stretch (it is primarily controlled by autonomic input). 
- Increased contractility (in the pharmacologic sense) is distinct: contractility implies autonomic or inotropic modulation, not the intrinsic length-dependent increase in force—though the Starling effect increases force, it is considered an intrinsic preload response rather than a change in contractility per se.
- Any choice claiming unlimited increase or no limits is incorrect because excessive stretch reduces efficiency.

6) Conclusion:
Therefore, within physiological limits, ventricular stretch leads to a greater force of contraction and a greater stroke volume, matching the provided answers.

More than one choice may be correct. Select all correct choices. Frank-Starling Law of the Heart states that, within limits, stretching of the walls of the ventricle before contraction will result in ____ at the next beat.多项选择题

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