What is the primary consequence of increasing ventricular muscle stretch within physiological limits?
Weaker contractions
Enhanced force of contraction
Reduced stroke volume
Decreased venous return
The Correct Answer is B
A. Weaker contractions: Within normal physiological limits, increasing ventricular stretch does not weaken contractions. Weak contractions may occur only if the muscle is overstretched beyond its optimal sarcomere length, which exceeds the Frank-Starling range.
B. Enhanced force of contraction: The Frank-Starling law of the heart states that increased ventricular filling stretches myocardial fibers, optimizing actin-myosin overlap within sarcomeres. This enhanced sarcomere alignment increases the force of contraction during systole, allowing the heart to eject a greater stroke volume in response to increased venous return.
C. Reduced stroke volume: Increasing ventricular preload within physiological limits actually increases stroke volume by enhancing contractile force. Stroke volume only decreases if the heart is overfilled beyond its optimal sarcomere length, leading to inefficient contraction.
D. Decreased venous return: Increasing ventricular stretch is a response to increased venous return, not a cause of decreased return. Venous return drives end-diastolic volume, which in turn stretches the ventricular muscle to regulate stroke volume according to the Frank-Starling mechanism.
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Related Questions
Correct Answer is {"dropdown-group-1":"A"}
Explanation
Correct answer: Left coronary
The left coronary artery arises from the left side of the ascending aorta, just above the aortic valve, and quickly branches to supply the heart muscle. Its two main branches are the anterior interventricular artery (also called the left anterior descending artery), which runs along the interventricular groove supplying the anterior walls of both ventricles, and the circumflex artery, which curves around the left side of the heart to supply the lateral and posterior walls of the left ventricle and left atrium. This anatomical arrangement ensures that oxygen-rich blood from the aorta is delivered efficiently to the majority of the left heart myocardium.
Correct Answer is C
Explanation
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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