UPSC NDA I 2015 General Ability Paper

Concept:The 'lub-dub' sound is produced by the closing of heart valves during the cardiac cycle.Explanation:The heart produces two distinct sounds, often described as 'lub' and 'dub'.The first sound, 'lub', is medically termed $S_1$ and is caused by the closure of the mitral and tricuspid valves at the beginning of systole (ventricular contraction).The second sound, 'dub', is termed $S_2$ and is caused by the closure of the aortic and pulmonic valves at the end of systole, marking the start of diastole.These sounds are heard through a stethoscope and indicate normal heart function.Thus, the 'lub-dub' sound is directly associated with the action of the heart.Answer:Heart