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The first heart sound is semilunar valves-
a. Closure of the tricuspid and bicuspid valves
b. Opening of the tricuspid and bicuspid valves
c. Opening of semilunar valves
d. Opening of eustachian valve

Last updated date: 13th Jun 2024
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Hint: Heart sounds are the noises created by the beating heart and the subsequent flow of blood through it. Specifically, the sounds reflect the turbulence induced when the heart valves snap shut.

Complete answer:
> Option A is correct. The first heart sound we hear is caused by the simultaneous closing of the bicuspid (mitral) valve and the tricuspid valve, both atrioventricular valves. It is similar to the word "LUBB" and is created due to the isometric period of contraction and the earlier part of the period of ejection.

> Option B is incorrect. The tricuspid and mitral valves open when the two atrium chambers contract, both of which allow blood to flow to the ventricles. When the two ventricle chambers contract, when the pulmonary and aortic valves open, they cause the tricuspid and mitral valves to close.

> Option C is incorrect. In order to direct blood flow through the heart, the semilunar valves work in conjunction with the AV valves. The semilunar valves are closed while the atrioventricular valves are open, and blood is pushed into the ventricles. The semilunar valves open when the AV valves close, pushing blood into the aorta and pulmonary artery.

> Option D is incorrect. In the superior portion of the inferior vena cava (IVC), the Eustachian valve (EV) is located and protrudes into the right atrial cavity. It is regarded as a functional valve in the foetus that helps guide oxygenated blood to the foramen ovale from the IVC, thus bypassing the pulmonary circulation.

Hence, the correct answer is option (A).

Note: Reverberation within the blood associated with the sudden block of flow reversal by the closure of the valves results in heart sounds. Because of this, auscultation is typically performed not at the location of the valve but at the location to which the sound waves reverberate to determine the function of a valve.