23.5: Heart Valves
The human heart is a complex organ with an intricate system of valves that regulate blood flow. There are two main types of valves: atrioventricular (AV) valves and semilunar valves.
The AV valves prevent the backflow of blood from the ventricles to the atria during ventricular contraction. These valves function with the assistance of the chordae tendineae and papillary muscles. When the ventricles are relaxed, the chordae tendineae are slack, allowing blood to flow from the atria into the ventricles without resistance. However, when the ventricles contract, the blood moving back toward the atria causes the cusps of the AV valves to close. The papillary muscles also contract, tensing the chordae tendineae and stopping the cusps before they swing into the atria. If either the chordae tendineae or the papillary muscles are damaged, regurgitation or backflow of blood into the atria could occur each time the ventricles contract.
The semilunar valves, on the other hand, prevent the backflow of blood from the pulmonary trunk and aorta into the right and left ventricles, respectively. Unlike the AV valves, the semilunar valves do not require muscular braces because the arterial walls do not contract, and the relative positions of the cusps remain stable. When these valves close, their three symmetrical cusps support each other like the legs of a tripod. When the aortic valve opens, the aortic sinuses prevent the individual cusps from sticking to the wall of the aorta.
However, any serious problems with these valves can disrupt the normal functioning of the heart. If valve function deteriorates to the point where the heart cannot maintain adequate circulatory flow, symptoms of valvular heart disease (VHD) may appear. This condition can be congenital, or it may develop after carditis, an inflammation of the heart.
