How is the lub sound made in heart?

The "lubb" sound in the heart, also known as the first heart sound, is primarily caused by the closure of the mitral (left atrioventricular) and tricuspid (right atrioventricular) valves at the beginning of systole. Here's how the lub sound is generated:

1. Start of Ventricular Contraction (Systole):

During systole, the ventricles of the heart contract, increasing the pressure within them.

2. Closure of Atrioventricular Valves:

The increased pressure in the ventricles forces the mitral and tricuspid valves to close to prevent the regurgitation (backward flow) of blood into the atria.

3. Blood Flow Turbulance and Vibrations:

The sudden closure of these valves creates turbulence in the blood rushing forward into the aorta (left ventricle) and the pulmonary artery (right ventricle). The turbulent blood flow and vibrations cause the valve tissues and the surrounding heart structures to vibrate.

4. Resonance of Heart Chambers:

The heart chambers, particularly the ventricles, act as resonating chambers that amplify and transmit the vibrations.

5. Transmission of Sound:

The vibrations are transmitted through the heart muscle, blood, and surrounding tissues. The left ventricular sound is best heard at the apex of the heart, while the right ventricular sound is best heard at the base of the heart near the sternum.

6. Perception as a "Lub" Sound:

These vibrations are perceived by the human ear as the low-pitched "lubb" sound.

It's important to note that while the "lub" sound is primarily caused by valve closure, other factors such as the tension and elasticity of the valves and the volume of blood in the ventricles also contribute to the overall sound.