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AV Valves and Semilunar Valves

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AV Valves and Semilunar Valves: An Introduction

By preventing the backward flow of blood from ventricles into the atria, the atrioventricular (AV) valves (mitral and tricuspid valves) divide the two atria and ventricles. Aortic and pulmonary valves, on another side, are the semilunar valves that divide the ventricles from big arteries like the aorta and pulmonary artery to stop the backward flow of blood from arteries into the ventricles.

Semilunar valves are made up of cusps that are self-supported as a result of their unique structure and position within the arteries, While, AV valves are made up of leaflets with specialised system support. The AV valves, which are attached to the ventricle walls through chordae tendineae prevent them from inverting, while in opposition to this, semilunar valves are fixed at the end of the aortic and pulmonary arteries.

Heart Valves

The purpose of heart valves is to maintain a unidirectional blood flow through the heart. Instead of being constructed of muscle, the valves are formed of stiff connective tissue layers which function as flaps. Two AV valves (mitral valve and tricuspid valve) and two semilunar valves (aortic valve and pulmonary valve) make up the four-heart valve. Due to pressure variations along both sides of the valve, the valves gently open and close. The valve's leaflets are forced to open whenever there is increased pressure behind it, allowing the blood to flow inside. However, when the pressure in front of the valve is higher, the leaflets snap shut and blood flow is blocked.

Heart Valves

Heart Valves

AV Valves

On each side of the heart, AV valves are located between the atrium and ventricles. These valves permit both the backflow of blood into the atrium during systole and the movement of blood from the atria to the ventricles. On the right side, the AV valve is named the tricuspid valve, which has three leaflets, while on the left side the valve is called as a mitral or bicuspid valve with two leaflets.

AV valves are forced to open and blood flows into the ventricles when the atrial pressure is higher than ventricular pressure. On the other hand, AV valves close rapidly when the ventricular pressure is greater than atrial pressure. The chordae tendineae, which are fibrous connective tissues which bind to the valves, prevent them from inverting.

AV Valves

AV Valves

Semilunar Valves

Semilunar valves get their name from the fact that they resemble a half-moon. They are situated between two main arteries and the ventricles. The pulmonary valve is situated between the right ventricle and pulmonary artery, whereas the aortic valve is situated between the left ventricle and aorta. Semilunar valves open when the ventricular pressure rises above arterial pressure due to the ventricle’s contraction, and blood is pushed into the major arteries. On the other hand, Semilunar valves close when the ventricles relax because arterial pressure is higher than ventricular pressure. The AV valves vs semilunar valves is described in the table below:

AV valves

Semilunar valves


AV valves are situated between the arteries and ventricles.

Semilunar valves are situated between the ventricles and main heart arteries.

Blood flow

It permits blood to flow from the left atrium to the left ventricle as well as from the right atrium to the right ventricle.

It permits blood to flow from the right ventricle to the pulmonary artery and from the left ventricle to the aorta.

Heart Sound

The first sound of the cardiac cycle, "LUBB," is produced when the valves close.

The second sound of the cardiac cycle, "DUB," is produced as the valves close.


Tricuspid and mitral.

Aortic and pulmonary.

Unique Feature

The chordae tendineae connective tissue to which, AV valves are connected inhibits them from inverting.

Such tissue is not seen.

Atrial systole in cardiac cycle

Valves open

Valves closed

Ventricle systole in cardiac cycle

Valves close

Valves open

What Is the Function of Valves?

The valves are open and close in response to the heart muscle contracting and relaxing. This permits alternating blood flow into the ventricles and atria, which helps in maintaining the proper blood flow and stops blood from flowing backwards.

Valve Disorders

Heart can suffer severe harm if the valves don't open and close properly, resulting in problems like the following:

  • Leaky Valve - The valve fails to close totally, allowing backward blood flow, so called regurgitation.

  • Stenosis - This entails restricted valve opening which doesn't open properly.

  • Atresia - It is a valve opening deformation that blocks the blood flow from the atria to the ventricle, or from the ventricle to the pulmonary artery or aorta.

Clinical Significance

The major purpose of heart valves is to ensure unrestricted, one-way blood circulation. Blood is pumped from the atria with low pressure to the ventricles with high pressure, which further supply the major arteries. During the constant movement of the cardiac cycle, compressive and longitudinal stresses cause valve tissue deformity, or dislocation. This deformity changes the sensitivity to physiological stimuli and susceptible genetics that can lead to valve failure.

Interesting Facts

It's interesting to note that every valve must be opened for blood to leave the chamber and closed to prevent blood from returning in the wrong direction. The valves may be harmed by disease occurrence or regular life span use.

Key Features

  • The major purpose of heart valves is to preserve unrestricted, one-way blood flow.

  • During the cardiac cycle, the AV and semilunar valves open and close, directing blood flow through the heart chambers and out to the rest of the body.

  • The differing framework of AV and Semilunar valves has a major influence on disorders and wellness.

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FAQs on AV Valves and Semilunar Valves

1. Do the semilunar and AV valves open simultaneously?

No, the semilunar and AV valves cannot open simultaneously. When semilunar valves are closed, the AV valves remain open. 

2. Do AV valves go by the name semilunar valves too?

Aortic and pulmonic valves are referred to as semilunar valves, and tricuspid and mitral valves are regarded as AV valves. Semilunar valves are the endocarditis flaps. Both valves close and open in response to the pressure in front and behind them.

3. Explain AV valve’s uniqueness in contrast to semilunar valve.

AV valves are built of leaflets, while semilunar valves are built of cusps. AV valves are fixed to the ventricle’s walls, but semilunar valves aren't ever fixed to the walls of arteries.

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