Heart valves located at the bases of the pulmonary trunk and aorta are called a. atrioventricular valves. b. semilunar valves. c. mitral valves. d. chordae tendineae.

The heart is a muscular organ that pumps blood throughout the body. It is divided into four chambers: the right atrium, right ventricle, left atrium, and left ventricle. There are four main valves in the heart that ensure one-way blood flow: the tricuspid valve, pulmonary valve, mitral (or bicuspid) valve, and the aortic valve.

1. Atrioventricular valves: These valves are located between the atria (top chambers) and ventricles (bottom chambers) of the heart. The tricuspid valve is between the right atrium and right ventricle, while the mitral valve is between the left atrium and left ventricle. These valves open when the heart is relaxed (diastole) to allow blood to flow into the ventricles and close during ventricular contraction (systole) to prevent blood from flowing back into the atria. 2. Semilunar valves: These valves are located at the exit points of the ventricles. The pulmonary valve is located at the base of the pulmonary trunk (which carries blood from the right ventricle to the lungs), while the aortic valve is situated at the base of the aorta (which carries oxygenated blood from the left ventricle to the rest of the body). These valves open when the ventricles contract, allowing blood to pass into the pulmonary trunk and aorta, and close when the ventricles relax to prevent blood from flowing back into the ventricles. 3. Mitral valve: Also known as the bicuspid valve, it is one of the atrioventricular valves specifically located between the left atrium and left ventricle. 4. Chordae tendineae: These are fibrous cords that attach the atrioventricular valves (tricuspid and mitral) to the ventricular muscle, preventing them from being pushed back into the atria when the ventricles contract.

Now that we have reviewed the functions of each valve and related structures, we can identify the correct option. The heart valves located at the bases of the pulmonary trunk and aorta are: a. atrioventricular valves. (Incorrect) b. semilunar valves. (Correct) c. mitral valves. (Incorrect) d. chordae tendineae. (Incorrect) So, the correct answer is option b. Semilunar valves.