Final answer:
The AV valves are supported by strong collagen cords called chordae tendineae, which connect to papillary muscles and prevent valve inversion and blood regurgitation during ventricular contraction.
Step-by-step explanation:
The AV (atrioventricular) valves are supported by strong collagen cords known as chordae tendineae. These tendinous cords, sometimes referred to as "heart strings," connect the valve flaps to the papillary muscles that extend from the inferior ventricular surface. Each flap of the tricuspid and mitral valves is connected to the chordae tendineae, which play a crucial role in preventing valve inversion and blood regurgitation during ventricular contraction. The papillary muscles in the ventricles contract to increase the tension in the chordae tendineae, ensuring that the valve flaps only open in the correct direction and thereby prevent backflow of blood into the atria.
In contrast, the semilunar valves (aortic and pulmonary valves) do not have chordae tendineae or papillary muscles. These valves are instead supported by pocket-like folds of endocardium, reinforced with extra connective tissue, which seal the openings when pressure changes occur during ventricular relaxation, preventing blood from flowing back into the ventricles.