Zoology - Body Fluids and Circulation Question with Solution | TestHub

When the contraction of ventricles occurs immediately after atrial systole, the pressure in the ventricles rises and closes the atrioventricular valves, preventing blood from returning to the atria. The pressure forces to open the semilunar valves of aorta and pulmonary artery to make entry of blood into these vessels, Oxygenated blood is pumped into the aorta and deoxygenated blood is pumped into the pulmonary artery.