The heart’s ability to pump blood efficiently relies on a precise system of one-way flow. Heart valves are specialized flaps of tissue situated within the heart that function as gates to manage this flow. Their primary role is to ensure that blood moves in a single, forward direction through the chambers and out into the circulation. This mechanism is accomplished by the valves opening to allow passage and then snapping shut to prevent blood from flowing backward, a process known as regurgitation.
The Two Functional Categories of Heart Valves
The four heart valves are grouped into two classifications based on their position and function. This grouping helps to understand their coordinated function during the cardiac cycle. The first group is the Atrioventricular (AV) valves, located between the upper chambers (atria) and the lower chambers (ventricles).
The second group is the Semilunar (SL) valves, found at the exit points of the ventricles. These valves guard the openings into the two major arteries that carry blood away from the heart. AV valves open when the atria contract and close when the ventricles contract, while SL valves operate in the opposite manner.
Valves Separating the Chambers
The two Atrioventricular valves control the movement of blood from the collecting chambers into the pumping chambers. The Tricuspid valve is situated on the right side of the heart, between the right atrium and the right ventricle. This valve consists of three cusps or leaflets, allowing deoxygenated blood to pass into the right ventricle. Its location is a starting point for the pulmonary circuit, which sends blood to the lungs.
The Mitral valve, also referred to as the Bicuspid valve, is located on the heart’s left side. It forms the barrier between the left atrium and the left ventricle. This valve possesses only two leaflets, unlike the three found in the Tricuspid valve. The Mitral valve governs the flow of oxygenated blood from the left atrium into the left ventricle, preparing it for distribution through the systemic circuit.
These two valves are anchored by tough, string-like structures called chordae tendineae, which connect the valve leaflets to small muscles in the ventricular walls. When the ventricles contract, these cords and muscles tighten to prevent the valve flaps from inverting into the atria, ensuring a tight seal and preventing backflow.
Valves Guarding the Exits
The two Semilunar valves are positioned where the ventricles connect to the main arteries, acting as the final gates for blood leaving the heart. The Pulmonary valve is located at the exit of the right ventricle, leading directly into the pulmonary artery. This position allows deoxygenated blood to be ejected from the right ventricle and sent toward the lungs.
The Aortic valve is situated at the exit of the left ventricle, connecting this chamber to the aorta, which is the body’s largest artery. When the left ventricle contracts, this valve opens to allow oxygen-rich blood to surge into the aorta for systemic circulation. The closure of the Aortic valve prevents this high-pressure blood from flowing back into the relaxing ventricle.
Both the Aortic and Pulmonary valves consist of three pocket-like cusps and lack the chordae tendineae found in the AV valves. They rely instead on the backward pressure of blood in the arteries to fill their cusps and force them shut.