Which of the following best describes the stroke volume (SV) of the heart?
The volume of blood remaining in the ventricle after ventricular systole
The pressure exerted by the left ventricle to open the aortic valve
The difference between end-diastolic volume (EDV) and end-systolic volume (ESV)
The total volume of blood in the ventricle before contraction
The Correct Answer is C
A. The volume of blood remaining in the ventricle after ventricular systole: This refers to the end-systolic volume (ESV), which is the amount of blood left in the ventricle after contraction. While ESV is a component used to calculate stroke volume, it does not itself represent the volume of blood ejected with each heartbeat.
B. The pressure exerted by the left ventricle to open the aortic valve: The pressure generated by the left ventricle during systole is termed ventricular systolic pressure. Although this pressure must overcome aortic pressure to allow ejection, it is a measure of force, not volume, and therefore does not define stroke volume.
C. The difference between end-diastolic volume (EDV) and end-systolic volume (ESV): Stroke volume represents the actual volume of blood ejected from the ventricle with each heartbeat. It is calculated as SV = EDV – ESV. EDV is the total ventricular volume at the end of filling, and ESV is the residual volume after contraction. This difference reflects effective cardiac output per beat.
D. The total volume of blood in the ventricle before contraction: The total volume of blood prior to contraction is the end-diastolic volume (EDV). While EDV contributes to determining stroke volume, it alone does not represent the volume of blood expelled during systole.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
Correct answer: True
During exercise, the sympathetic nervous system stimulates the sinoatrial (SA) node, which is located in the right atrium and functions as the heart’s natural pacemaker, leading to an increase in heart rate. This physiological response enhances cardiac output to meet the increased metabolic demands of skeletal muscles, delivering more oxygen and nutrients while removing carbon dioxide and metabolic waste. After exercise ceases, parasympathetic (vagal) tone gradually predominates, slowing SA node firing and allowing the heart rate to return toward its resting baseline. This recovery reflects normal autonomic regulation of cardiovascular function.
Correct Answer is C
Explanation
A. Contractile force increases to compensate for the reduced cardiac output: In early compensatory phases, the heart may attempt to increase contractility via sympathetic stimulation, but in true heart failure, the myocardium is unable to generate sufficient force due to structural or functional impairment.
B. Contractile force increases, leading to an increased end systolic volume: Increased contractility would reduce, not increase, end-systolic volume because more blood is ejected per beat. In heart failure, contractile weakness leads to higher end-systolic volumes, reflecting incomplete emptying of the ventricles.
C. Contractile force is diminished due to damaged cardiomyocytes or cardiomyopathies: Heart failure results from conditions such as myocardial infarction, chronic hypertension, or dilated cardiomyopathy that impair cardiomyocyte function. This reduces the strength of ventricular contraction, decreasing stroke volume and overall cardiac output.
D. Contractile force is not affected in heart failure: Contractile force is significantly affected in heart failure. The weakened myocardium cannot generate sufficient pressure to maintain normal stroke volume, making this statement inaccurate.
E. Contractile force remains the same, but the heart becomes larger: While ventricular dilation can occur in chronic heart failure as a compensatory mechanism (eccentric hypertrophy), the contractile force per myocyte is reduced. Increased chamber size alone does not preserve effective contraction.
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