Question

First cardiac sound (lub) is associated with (a) Closure of tricuspid and bicuspid valves (b) Opening of tricuspid valves (c) Closure of semilunar valves (d) Opening of semilunar valves

Short answer

The first cardiac sound (lub) is associated with (a) Closure of tricuspid and bicuspid valves.

Step-by-step solution

Knowledge of the Cardiac Cycle

Understand that the cardiac cycle includes a set of events taking place in the heart in one complete heartbeat. In one cardiac cycle, the heart undergoes systole (contraction) and diastole (relaxation) which causes the heart sounds.

Identify the First Cardiac Sound

The first cardiac sound (lub) is heard when the atrioventricular valves, which include the tricuspid and bicuspid valves, close. This happens at the start of the ventricular systole, when the ventricles start to contract.

Match the Correct Option

After understanding the cardiac cycle and the cause of the first cardiac sound, one can match this information with the answer options provided in the exercise. The correct answer would be (a) Closure of tricuspid and bicuspid valves, which corresponds to the cause of the first heart sound.

Key concepts

Heart Sounds

Heart sounds are important audible indicators of how well our heart functions. When you place a stethoscope on the chest, you can hear these sounds, often described as "lub-dub." These sounds are produced by the heart valves opening and closing with each heartbeat. The first sound, "lub," is known as S1. This sound is caused by the closure of the atrioventricular valves—the tricuspid and bicuspid (or mitral) valves. The closure of these valves marks the beginning of ventricular systole, or the contraction phase of the heart. In contrast, the second sound, "dub," is labeled S2 and is generated by the closure of the semilunar valves (aortic and pulmonary valves). Listening to these heart sounds helps doctors assess heart health and identify issues related to valve function.

• The 'lub' corresponds to the closure of the atrioventricular valves.
• The 'dub' corresponds to the closure of the semilunar valves.
• Heart sounds are used to monitor cardiac function.

Atrioventricular Valves

Atrioventricular (AV) valves play a crucial role in the cardiac cycle. They include the tricuspid valve, located on the right side of the heart, and the bicuspid (or mitral) valve, situated on the left. These valves act as gateways between the atria and the ventricles. During the heart's relaxation phase, known as diastole, the AV valves open, allowing blood to flow from the atria into the ventricles. When the heart transitions to its contraction phase, or systole, the AV valves close to prevent backflow of blood into the atria.
The proper functioning of the AV valves is essential for maintaining efficient blood flow throughout the cardiac cycle. If these valves don't close properly, it could lead to blood leakage or regurgitation, affecting circulation efficiency and potentially leading to heart murmurs.

• AV valves prevent backflow into atria during ventricular contraction.
• They include the tricuspid and mitral valves.
• Their closure results in the first heart sound, "lub."

Ventricular Systole

Ventricular systole is a critical phase of the cardiac cycle where the heart's ventricles contract. This contraction is essential because it pumps oxygen-rich blood from the left ventricle into the aorta and throughout the body, and deoxygenated blood from the right ventricle into the pulmonary artery and towards the lungs. The onset of ventricular systole is marked by the closure of the atrioventricular valves, producing the first heart sound "lub." This indicates that the ventricles are now contracting, forcing blood out of the heart.
During this process, the semilunar valves, which include the aortic and pulmonary valves, open to allow the ejection of blood from the heart. After the ventricles have finished contracting, these semilunar valves close, producing the second heart sound, "dub." This sound marks the end of ventricular systole and the beginning of the heart's relaxation phase, diastole.

• Ventricular systole is the contraction phase of the ventricles.
• The process ensures efficient blood flow throughout the body and lungs.
• It starts with the closing of AV valves and ends with the opening and closing of semilunar valves.