The diagram given below represents a section of the human heart. Answer the questions that follow: The diagram given below represents a section of the human heart. Answer the questions that follow:
What causes the heart sounds ‘LUBB’ and ‘DUP’?
Topic: Heart sounds
Answer
"LUBB" — the first sound, longer and duller. It is produced when the ATRIOVENTRICULAR valves (tricuspid and bicuspid) close sharply at the start of VENTRICULAR SYSTOLE.
"DUP" — the second sound, short and sharp. It is produced when the SEMILUNAR valves at the roots of the aorta and pulmonary artery close at the beginning of VENTRICULAR DIASTOLE.
THE ESSENTIAL POINT: both sounds are made by valves CLOSING, never opening. That single fact eliminates half the wrong answers students give.
Name the VALVES and the PHASE for each — both are needed.
The order makes sense if you follow the blood: the valves close in the same sequence the blood travels — first those between atrium and ventricle (LUBB), then those at the exits into the arteries (DUP).
THE MEDICAL RELEVANCE, worth a closing line: a "MURMUR" means a valve is leaking or not closing properly, so a doctor listening to the chest with a stethoscope is checking the valves.