2nd hea sound is due to: (A) Closure of AV valves, (B) Closure of aoic valve, (C) Inthrushing of blood, (D) Atrial contraction
Answer is B. The second is a shoer, high-pitched "dup" (second sound), caused by vibrations associated with the closure of the aoic and pulmonary valves just after the end of ventricular systole.Ref: Ganong&;s Review of medical physiology 25th edition. Page: 542