EVERYDAY SCIENCE

Detailed explanation-1: -Semilunar valves are not associated with the papillary muscles, and are not actively closed.

Detailed explanation-2: -Semilunar valves are not associated with the papillary muscles, and are not actively closed.

Detailed explanation-3: -Tricuspid and mitral valves are atrioventricular valves. These valves are actively closed by the papillary muscles (when the ventricles contract) to prevent backflow into the artia.

Detailed explanation-4: -The semilunar valves are closed because the ventricular pressure is lower than that in the aorta and the pulmonary artery (fig. 1.1). The contraction is represented by a colour change of myocardium. The ventricles contract and all valves are closed, so no blood can be ejected.

Detailed explanation-5: -However, when the ventricles relax, arterial pressure exceeds ventricular pressure and the semilunar valves snap shut. This is due to the elevated pressures in the aorta and the pulmonary artery pushing the blood back toward the ventricles to close the semilunar valves.