The heart functions as a pump, moving blood throughout the body in a continuous, one-way circuit. Specialized valves regulate this flow, ensuring blood travels forward and never backward. The atrioventricular (AV) valves are positioned at the entry points of the lower chambers, acting as gateways between the collecting upper atria and the powerful pumping ventricles. These valves maintain the necessary unidirectional flow of blood from the atria into the ventricles. Their proper function is integral to the heart’s ability to generate sufficient pressure to circulate oxygen and nutrients throughout the body.
Identifying the Two Atrioventricular Valves
The two atrioventricular valves are distinct structures located on opposite sides of the heart, separating the atrium from the ventricle on each side. On the right side, between the right atrium and the right ventricle, is the tricuspid valve. This valve is named for its composition of three leaflets or cusps, which control blood passing into the right ventricle. These cusps open and close to regulate flow.
The left side of the heart houses the mitral valve, positioned between the left atrium and the left ventricle. This structure is also commonly referred to as the bicuspid valve because it is composed of only two leaflets. Since the left side manages oxygenated blood destined for the entire body, the mitral valve must withstand significantly higher pressures.
How the Valves Control Blood Flow
The opening and closing mechanism of the atrioventricular valves is not an active muscular process but rather a passive reaction governed entirely by pressure differences within the heart chambers. When the atria are filled with blood, the pressure within them exceeds the pressure in the relaxed ventricles below, causing the AV valves to open and allow blood to flow downward for filling. This state is known as ventricular diastole, or the resting phase.
As the ventricles contract during ventricular systole, the pressure inside them rises sharply, immediately pushing the valve leaflets upward toward the atria. This sudden change in the pressure gradient forces the leaflets to snap shut, effectively sealing the opening between the two chambers. To prevent the leaflets from inverting or “prolapsing” into the higher-pressure atria, the valves rely on a specialized support system.
The support system consists of the chordae tendineae, which are tough, inelastic fibrous cords. These cords connect the valve leaflets to muscular projections within the ventricles called papillary muscles. When the ventricles contract, the papillary muscles also contract, pulling on the chordae tendineae to maintain tension. This action ensures the valve remains securely closed against high ventricular pressure, preventing backflow into the atria.
When Atrioventricular Valves Malfunction
When the structure and function of the AV valves are compromised, two primary types of malfunction can occur, both disrupting the heart’s efficiency. The first is stenosis, which happens when the valve leaflets become stiff, thickened, or fused together, causing the valve opening to narrow. This obstruction forces the upstream atrium to work harder to push blood through the smaller opening, which can lead to strain and enlargement of that chamber.
The second common malfunction is regurgitation, also referred to as insufficiency or a leaky valve. This occurs when the leaflets fail to close completely, allowing blood to flow backward into the atrium during ventricular contraction. This failure significantly reduces the heart’s forward pumping capacity and leads to inefficient circulation.
These valve problems often manifest through symptoms related to the heart’s reduced output and congestion of blood upstream. Common signs include shortness of breath, particularly during physical activity or when lying flat, as well as chronic fatigue and dizziness. An irregular heartbeat or chest pain can also indicate a significant valve issue.
A physician can often detect a potential valve malfunction during a physical exam by listening to the heart with a stethoscope. A heart murmur, which is an unusual sound caused by turbulent blood flow, is frequently the first sign of a valve problem. If a murmur is detected, a non-invasive imaging test called an echocardiogram is used to visualize the valve structure and function in real-time. This test allows doctors to precisely measure the degree of narrowing in stenosis or the amount of backflow in regurgitation to determine the severity of the condition.