ATricuspid valve
BSemilunar valves
CBicuspid valve
DTricuspid and bicuspid valves
Answer:
B. Semilunar valves
Read Explanation:
The heart produces two primary sounds during the cardiac cycle, referred to as 'lubb' (S1) and 'dubb' (S2).
S1 (Lubb): This sound is generated by the closure of the atrioventricular (AV) valves (the bicuspid/mitral valve and the tricuspid valve) at the beginning of ventricular systole. This marks the onset of ventricular contraction.
S2 (Dubb): This sound is caused by the sudden closure of the semilunar valves (aortic and pulmonary valves) at the end of ventricular systole.
Timing: S2 occurs at the end of the ventricular ejection phase, marking the start of ventricular diastole (relaxation).
Mechanism: When the pressure in the ventricles falls below the pressure in the aorta and pulmonary artery, the backflow of blood forces the semilunar valves to snap shut, producing the characteristic 'dubb' sound.
Component Splitting: The S2 sound is often heard as two distinct components: A2 (aortic valve closure) and P2 (pulmonary valve closure). A2 typically occurs slightly before P2. This interval may increase during inspiration, a phenomenon known as physiological splitting.
Comparison Summary
Sound | Clinical Term | Valve Closure Involved | Cardiac Phase |
|---|---|---|---|
First Sound | S1 (Lubb) | Atrioventricular (AV) | Onset of Systole |
Second Sound | S2 (Dubb) | Semilunar (SL) | Onset of Diastole |