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Correct Answer: stroke volume multiplied by the
heart rate.
the main function of the heart—or cardiac muscle—is to pump blood throughout the body by contracting and relaxing in a rhythmic manner. the efficiency with which the heart performs this task is quantified using a measure known as cardiac output. cardiac output is crucial because it reflects the amount of blood the heart can pump in a given timeframe, thus determining the ability of the cardiovascular system to meet the body’s demands for oxygen and nutrients.
cardiac output is calculated by multiplying two key factors: the stroke volume and the heart rate. stroke volume refers to the amount of blood ejected from the left ventricle of the heart with each contraction. heart rate, on the other hand, is the number of times the heart beats per minute. therefore, the formula for cardiac output (co) is expressed as co = stroke volume (sv) × heart rate (hr). this formula highlights that the total volume of blood pumped by the heart per minute is dependent on both the volume of blood moved with each heartbeat and the frequency of the heartbeats.
to understand why the correct answer is "stroke volume multiplied by the heart rate," consider the following: if either the stroke volume or the heart rate increases, the cardiac output will also increase, assuming the other factor remains constant. this relationship allows the body to adjust cardiac output based on physical activity, stress, and other conditions. for example, during exercise, the heart rate typically increases, and the stroke volume can also increase up to a certain point, leading to a higher cardiac output to meet the increased demand for blood and oxygen by various muscles.
it’s important to clarify why the other options do not correctly describe cardiac output:
- "stroke volume divided by the heart rate" suggests an inverse relationship between heart rate and cardiac output, which is incorrect as they are directly proportional.
- "pressure of the blood against the artery walls during contraction of the heart" and "during relaxation of the heart" describe systolic and diastolic blood pressures, respectively, not cardiac output. blood pressure is influenced by cardiac output but also depends on other factors like the resistance of blood vessels.
in summary, cardiac output is a fundamental measure of heart function and is essential for understanding how well the heart can supply blood to meet the body's needs. it is accurately calculated as the product of stroke volume and heart rate, providing a clear picture of the heart’s pumping efficiency.
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