Question

what causes the second heart sound, called s2 or \dub\?
closing of the valves that connect the atria and ventricles in the heart
closing of the valves that connect the heart to the pulmonary artery and aorta
opening of the valves that connect the atria and ventricles in the heart
opening of the valves that connect the heart to the pulmonary artery and aorta

Explanation:

The second heart sound (S2 or "Dub") is caused by the closing of the semilunar valves (pulmonary and aortic valves) which connect the heart to the pulmonary artery and aorta. The first heart sound (S1 or "Lub") is from atrioventricular valve closure. So we analyze each option:

• Option 1: Closing atrioventricular valves causes S1, not S2. Eliminate.
• Option 2: Semilunar valves (connect heart to pulmonary artery and aorta) close to produce S2. This matches.
• Option 3: Opening of atrioventricular valves doesn't produce S2. Eliminate.
• Option 4: Opening of semilunar valves doesn't produce S2. Eliminate.

Answer:

B. Closing of the valves that connect the heart to the pulmonary artery and aorta