Final answer:
The heart features four valves that maintain unidirectional blood flow: two atrioventricular valves (tricuspid and mitral) connected by chordae tendineae to papillary muscles and two semilunar valves (pulmonary and aortic) composed of endocardium folds. The valves open and close in response to heart muscle pressure changes, preventing blood backflow.
Step-by-step explanation:
Cardiac Valves and Their Function
The heart is an organ that ensures the unidirectional flow of blood, and this is achieved through the function of the cardiac valves. The heart has four main valves: two atrioventricular valves (the right tricuspid valve and the left mitral valve) and two semilunar valves (the pulmonary valve and the aortic valve). The tricuspid valve, located between the right atrium and the right ventricle, consists of three leaflets or flaps that are connected to papillary muscles by the chordae tendineae. These structures prevent the backflow of blood by opening and closing in response to variations in heart muscle pressure.
The semilunar valves, on the other hand, do not have chordae tendineae or papillary muscles. They are made of pocket-like folds of endocardium reinforced with additional connective tissue. These valves open to allow blood to be ejected from the ventricles into the arteries and close to prevent blood from flowing backward into the heart. During the heart's relaxation phase, atrioventricular valves are open to allow blood to move from the atria to the ventricles, and the semilunar valves are closed to prevent regurgitation. When the ventricles contract, the atrioventricular valves close, and the semilunar valves open, allowing blood to flow into the pulmonary artery and aorta.