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Multiple Choice
Which of the following factors does NOT influence stroke volume in the cardiovascular system?
A
Preload
B
Thyroid hormone levels
C
Contractility
D
Afterload
Verified step by step guidance
1
Understand the concept of stroke volume: Stroke volume is the amount of blood ejected by the left ventricle during each contraction. It is influenced by three primary factors: preload, contractility, and afterload.
Define preload: Preload refers to the degree of stretch in the cardiac muscle fibers before contraction, which is determined by the volume of blood returning to the heart (venous return). Increased preload generally increases stroke volume.
Define contractility: Contractility is the strength of the heart's contraction, influenced by factors such as calcium availability and sympathetic nervous system activity. Increased contractility enhances stroke volume.
Define afterload: Afterload is the resistance the heart must overcome to eject blood during systole. Higher afterload decreases stroke volume because the heart has to work harder to pump blood.
Clarify the role of thyroid hormone levels: Thyroid hormones primarily influence metabolic rate and heart rate but do not directly affect stroke volume. Therefore, thyroid hormone levels are not considered a direct factor influencing stroke volume.