Final answer:
The tricuspid and mitral valves are anchored by chordae tendineae, which are crucial for preventing backflow of blood. These are required for the atrioventricular valves to withstand the high pressure during ventricular contraction without prolapsing, unlike the semilunar valves that do not need these structures to prevent backflow.
Step-by-step explanation:
The valves that are anchored by chordae tendineae are the atrioventricular valves, which include the tricuspid valve and the mitral valve. These strings of heart tissue, composed predominantly of collagenous fibers, are crucial for preventing the backflow of blood from the ventricles to the atria during the heart's contraction phase. Unlike the atrioventricular valves, the semilunar valves (aortic and pulmonary) do not require chordae tendineae because their unique structure allows them to close effectively and prevent backflow due to the pressure changes as the ventricles relax.
Why are chordae tendineae more critical for atrioventricular valves?
The presence of chordae tendineae is more critical for the atrioventricular valves than for the semilunar valves because they must resist higher pressures within the ventricles. During ventricular contraction, the chordae tendineae and the associated papillary muscles work together to prevent the inversion or prolapse of the valves, thus ensuring that blood flows in the correct direction and does not re-enter the atria. This is not necessary for the semilunar valves, as their structure, with pocket-like cusps, allows them to seal effectively with changes in pressure.