Final answer:
Stroke volume (SV) is influenced by venous return and sympathetic activity, with the extent of venous return impacting preload and contractility influenced by the sympathetic nervous system.
Step-by-step explanation:
The stroke volume (SV) is determined by the volume of venous return to the heart and the impact of sympathetic activity on the heart. Venous return affects the preload, which is the initial stretching of the cardiac myocytes prior to contraction, thus influencing the end-diastolic volume (EDV). The sympathetic nervous system, through the release of catecholamines such as epinephrine and norepinephrine, increases heart contractility, which affects the end-systolic volume (ESV). The difference between EDV and ESV represents the SV. Additionally, the autonomic nervous system and various hormones regulate the contractility of the heart, influencing SV.
Cardiac Output (CO) is the product of heart rate (HR) multiplied by SV, and it is a measure of the efficiency of the heart as a pump. Factors that increase CO, such as exercise or stress, often do so through increasing either HR or SV or both, which in turn can elevate blood pressure and enhance blood flow.
In summary, SV is closely linked to the function of the heart and the circulatory system, being modulated by both the extent of venous return and the level of sympathetic activity. Thus, the correct answer to the question is 5) the extent of venous return and by sympathetic activity.