What does the Frank-Starling Law describe?

What does the Frank-Starling Law describe?

• A. As EDV increases, the heart wall stretches more, leading to a greater force of contraction and increased stroke volume.
• B. As EDV increases, afterload increases, decreasing stroke volume.
• C. As EDV decreases, contractility increases.
• D. As heart rate increases, preload increases.

Answer: (A)

The key idea is how filling the ventricle affects its pumping strength. When the ventricles receive more blood during diastole, the end-diastolic volume increases and the muscle fibers are stretched to a longer length. Cardiac muscle generates a stronger contraction when stretched toward that optimal length, so the force of contraction rises and more blood is ejected with each beat, increasing stroke volume. This is the Frank–Starling mechanism: the heart adjusts its output to match the amount it receives, within normal limits. The other statements describe different influences—afterload opposing ejection, EDV decreasing not increasing contractility, and heart rate affecting filling time—not the length-dependent force relationship that links higher EDV to a stronger contraction and greater stroke volume.

The key idea is how filling the ventricle affects its pumping strength. When the ventricles receive more blood during diastole, the end-diastolic volume increases and the muscle fibers are stretched to a longer length. Cardiac muscle generates a stronger contraction when stretched toward that optimal length, so the force of contraction rises and more blood is ejected with each beat, increasing stroke volume. This is the Frank–Starling mechanism: the heart adjusts its output to match the amount it receives, within normal limits. The other statements describe different influences—afterload opposing ejection, EDV decreasing not increasing contractility, and heart rate affecting filling time—not the length-dependent force relationship that links higher EDV to a stronger contraction and greater stroke volume.