The atrioventricular valves will be open whenA. Atria are in diastole and ventricles are in systole B. Pressure in the ventricles is greater than the pressure in the great arteries C. The ventricles are being passively filled D. The ventricles are in isovolumetric contraction
Answer: (c) The ventricles are being passively filled. During diastole, a normally-functioning mitral valve opens as a result of increased pressure from the left atrium as it fills with blood (preloading). As atrial pressure increases above that of the left ventricle, the mitral valve opens. Opening facilitates the passive flow of blood into the left ventricle. Diastole ends with atrial contraction, which ejects the final 20% of blood that is transferred from the left atrium to the left ventricle. This amount of blood is known as end diastolic volume (EDV), and the mitral valve closes at the end of atrial contraction to prevent a reversal of blood flow. Mitral valve also opens when right ventricle is passively filled.
C. When the ventricles are being passively filled, the valves between the atria and ventricles (atrioventricular valves) will need to open. When pressure in the ventricles is higher than in the arteries, blood will flow into the arteries - there is blood exiting the ventricles, so the ventricles are contracting, so the atrioventricular valves need to be closed to stop backflow of blood into the atria. When atria are in diastole (filling) and ventricles are in systoles (emptying), the situation is the same as I just described for B.
