ANATOMY

Detailed explanation-1: -The semilunar valves are closed and the atrioventriular valves are open during diastole. The right atrium receives blood flowing from the systemic venous system via the superior and inferior venae cavae. This blood initially passes passively through the right atrioventricular orifice into the right ventricle.

Detailed explanation-2: -Diastole begins with the closing of the aortic valve (or pulmonic) and ends with the closing of the mitral valve (or tricuspid). This period encompasses the ventricular relaxation and filling. Diastole represents when the blood vessels return blood to the heart in preparation for the next ventricular contraction.

Detailed explanation-3: -Pulmonary semilunar valves are closed during systole.

Detailed explanation-4: -The semilunar valves act to prevent backflow of blood from the arteries to the ventricles during ventricular diastole and help maintain pressure on the major arteries.

Detailed explanation-5: -As the ventricles contract, ventricular pressure exceeds arterial pressure, the semilunar valves open and blood is pumped into the major arteries. However, when the ventricles relax, arterial pressure exceeds ventricular pressure and the semilunar valves snap shut.