Question

Assertion: Starting of ventricular diastole leads to closure of semi lunar valves. Reason: Ventricular diastole leads to fall in ventricular pressure.

Short answer

Yes, the claim is correct. In the stage of ventricular diastole, the ventricles are at rest, causing a decrease in ventricular pressure. When this pressure falls below the pressure in the aorta or pulmonary artery, the semi lunar valves close to prevent the backflow of blood.

Step-by-step solution

Understand what 'ventricular diastole' means

Ventricular diastole is a stage in the cardiac cycle where the ventricles of the heart are at rest and they are being filled with blood. This stage follows the ventricular systole stage where the ventricles contract to pump blood to the body.

Understand the effect of ventricular diastole on ventricular pressure

During ventricular diastole, since the ventricles are at rest and they are filling up with blood, the pressure within the ventricles decreases. This decreasing pressure is due to the lack of forceful contraction of the ventricular muscle.

Understand the effect of ventricular pressure on the state of semi lunar valves

Heart valves, including the semi lunar valves, function under a simple pressure system - they open and close responsive to the pressure gradients across the valve. When the pressure in the ventricles falls below the pressure in the aorta and pulmonary artery, due to ventricular diastole, the semi lunar valves close to prevent backflow of blood.

Key concepts

Cardiac Cycle

The cardiac cycle is the series of events that occur in the heart with each heartbeat. It's essential to understand this cycle to appreciate the intricate processes that take place including ventricular diastole.

The cycle can be divided into two main phases: systole and diastole. During systole, the heart muscles contract to pump blood out of the ventricles and into the arteries. In contrast, diastole is the phase where the heart muscles relax and the ventricles fill with blood from the atria. The entire cycle is critical for maintaining the flow of blood throughout the body, and any disruption in this process can have significant consequences for cardiovascular health.

In the context of an exercise to illustrate ventricular diastole, it's key when conceptualizing the cardiac cycle to also understand the timing of the valve operations which are intrinsically linked to the pressures within the heart chambers.

Ventricular Pressure

Ventricular pressure plays a pivotal role in the mechanics of the heart's function. During the cardiac cycle, the changes in ventricular pressure are what primarily drive the opening and closing of heart valves.

Specifically, during ventricular diastole, the ventricles are in a relaxed state and the heart is in a period of filling. Consequently, as they fill with blood, the pressure inside the ventricles is relatively low compared to the pressure in the arteries. It's this gradient in pressure that is instrumental to the normal direction of blood flow and proper valve function.

The heart relies on this system of pressure changes and plays a fundamental role in ensuring that blood is efficiently circulated, with oxygen-rich blood being sent throughout the body and oxygen-depleted blood being directed to the lungs.

Semi Lunar Valves

The semi lunar valves are crucial components within the heart structure. Located at the exit of each ventricle, these valves include the aortic valve and the pulmonary valve. They play a vital part by controlling blood flow from the heart into the aorta and the pulmonary artery.

During ventricular diastole, when ventricular pressure falls as the heart's chambers relax, these semi lunar valves close. This closure prevents the backflow of blood into the ventricles.

The Importance of Timing

It is the precise timing of the closing and opening of these valves that ensures the unidirectional flow of blood and the efficient functioning of the cardiac cycle. If the semi lunar valves do not function properly, it can lead to conditions like regurgitation, where blood leaks back into the heart chambers, which can over time lead to heart failure.