Starling's law of the heart states that, within limits, the longer, or more stretched, the heart fibers are at the beginning of the contraction, the
weaker the contraction.
slower the heart rate.
faster the heart rate.
stronger the contraction.
The Correct Answer is D
A. weaker the contraction: This is the opposite of the law; a lack of stretch usually results in a weaker stroke volume.
B. slower the heart rate: Starling's Law deals with stroke volume (the force of the pump), not the electrical timing of the heart rate.
C. faster the heart rate: Heart rate is primarily controlled by the SA node and the autonomic nervous system, not fiber stretch.
D. stronger the contraction: Also known as the Frank-Starling mechanism, this law states that the more the cardiac muscle is stretched (due to increased blood filling the heart), the more forcefully it will contract to pump that blood out.
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Related Questions
Correct Answer is {"dropdown-group-1":"B"}
Explanation
A. Spectrin: As noted earlier, this is a protein that helps maintain the shape of red blood cells.
B. Hematocrit: A hematocrit test measures the "packed cell volume" to see what percentage of whole blood is made up of red blood cells.
C. Hematopoiesis: This is the physiological process of blood cell formation, not a measurement.
D. Hemocytometer: This is a specialized slide used to count individual cells under a microscope, but it does not measure the volume percentage directly like a centrifuge/hematocrit.
Correct Answer is B
Explanation
A. rapid to appear but short-lived: This describes the nervous system, which uses electrical impulses for near-instant but brief effects.
B. slow to appear but long-lasting: Hormones must travel through the bloodstream to reach targets, which takes time, but their effects can persist for hours or even days.
C. rapid to appear and long-lasting: Very few biological systems act both instantly and for long durations simultaneously.
D. slow to appear and short-lived: This would be an inefficient regulatory system; endocrine effects are typically sustained.
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