Question

when lub-dub occur in heart? EXPLAIN

Answer 1

Normally M1 precedes T1 slightly. It is caused by the closure of the atrioventricular valves, i.e. tricuspid and mitral (bicuspid), at the beginning of ventricular contraction, or systole. When the ventricles begin to contract, so do the papillary muscles in each ventricle.

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Answer 2

The mitral (bicuspid) and tricuspid valves between the atria and ventricles close to avoid back flow of the blood to the atria when the ventricles contract. This causes the first sound, S1, or as it is heard, “lub.”

The semilunar valves (at the exits of the ventricles) close to prevent blood backflow from arteries caused by lower pressure in the ventricles as the ventricles expand to fill with blood before pumping it. This causes the S2, or “dub” sound.