The second heart sound is due to?

Appeared in: HPSSC - 2015

Explanation

The second heart sound (S2), often described as "dub," marks the end of ventricular systole and the beginning of diastole.
It is produced by the closure of the two semilunar (SL) valves: the aortic valve and the pulmonary valve.
The sound has two components: A2 (aortic valve closure) and P2 (pulmonary valve closure).
Since the aortic valve is a semilunar valve and is listed as an option, it is the correct answer for the cause of the second heart sound.

Option B: The closure of the tricuspid valve, an atrioventricular (AV) valve, contributes to the first heart sound (S1 or "lub"), not the second.
Option C: The closure of the mitral valve, an atrioventricular (AV) valve, is the main component of the first heart sound (S1 or "lub"), not the second.
Option D: The foramen ovale is a shunt in the fetal heart that allows blood to bypass the pulmonary circulation. It normally closes after birth and is not a valve that produces normal heart sounds in an adult.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of Heart Sounds as background academic context rather than a clinical decision trigger.
Auscultating heart sounds is a fundamental nursing assessment skill used to detect abnormalities like murmurs, gallops, or clicks, which can indicate valvular disease, heart failure, or other cardiac pathologies.
Identifying the characteristics of S1 and S2 (intensity, splitting, pitch) at different locations on the chest helps in diagnosing specific cardiac conditions.
What if? If a nurse auscultates a 'split S2' that widens with inspiration and narrows with expiration, this is a normal physiological finding. However, a 'fixed split S2' (one that does not change with respiration) is abnormal and can be a sign of an Atrial Septal Defect (ASD).

How to Approach the Question

First, identify the core concept being tested. The question asks for the physiological cause of the second heart sound (S2).
Recall the events of the cardiac cycle and the associated sounds, often remembered by the mnemonic 'lub-dub'.
Remember that 'lub' is the first heart sound (S1), caused by the closure of the atrioventricular (AV) valves (mitral and tricuspid).
Remember that 'dub' is the second heart sound (S2), caused by the closure of the semilunar (SL) valves (aortic and pulmonary).
Evaluate the given options based on this knowledge. The aortic valve is a semilunar valve. The mitral and tricuspid valves are AV valves. The foramen ovale is a fetal structure, not a valve involved in adult heart sounds.
Conclude that the closure of the aortic valve is a cause of the second heart sound.

Concept Tested & Keywords

QNsl1SB5PkSKwMfyoMVShQ

E6 Physiology Guyton 4SAE Part 2A p. 12-13

E6 Physiology Ganong 27e Vol 2 Part 1 p. 98-100

E6 Nelson Textbook of Pediatrics(2024) — Volume 2 p. 531-533

Practise the full HPSSC - 2015

Attempt every question from this paper in a timed mock, then review the full solution for each one.