Human Heart: Structure and Working · NCERT Biology

The first heart sound 'Lubb' is associated with:

  1. Closure of the semilunar valves at start of diastole
  2. Opening of the atrio-ventricular valves during filling
  3. Closure of the tricuspid and bicuspid valves
  4. Opening of the semilunar valves during systole
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Correct answer: Closure of the tricuspid and bicuspid valves

The first heart sound (Lubb) is produced during ventricular systole. It is caused by the sudden closure of the tricuspid and bicuspid (AV) valves to prevent backflow of blood into the atria.

Difficulty: Medium Question 8 of 20

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