"lub" sound is produced after _________ ?
Correct answer: C. The bicuspid and tricuspid valves suddenly close
- A. The ventricles are fully contracted
- B. The ventricles start to relax
- C. The bicuspid and tricuspid valves suddenly close
- D. The semilunar valves are closed
Explanation
The “lub” sound is produced when the atrioventricular valves, the bicuspid and tricuspid valves, suddenly close at the beginning of ventricular systole. Students often choose d because the semilunar valves also close during the cardiac cycle, but their closure produces the “dub” sound.
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About Cardiac Cycle and Heartbeat
The cardiac cycle describes atrial systole, ventricular systole and diastole, including pressure changes, blood movement and the opening or closing of heart valves. It also covers the conduction pathway from the sinoatrial node through the atrioventricular node, bundle of His and Purkinje fibres, and relates these events to heartbeat sounds.
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