The first heart sound, lubb, is produced by
Correct answer: D. the closure of the atrioventricular valves at the start of ventricular systole
- A. blood rushing into the atria
- B. the closure of the semilunar valves
- C. contraction of the atrial walls
- D. the closure of the atrioventricular valves at the start of ventricular systole
Explanation
When the ventricles begin to contract the pressure inside them rises above atrial pressure, the tricuspid and bicuspid valves snap shut and the vibration gives the long low lubb. The shorter, sharper dupp comes later, when the semilunar valves close at the end of ventricular systole. A murmur heard between these sounds usually means a valve is leaking or narrowed.
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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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