Answer
Two valves in the heart prevent blood from flowing backward from the arteries into the ventricles. There is another set of valves that prevent the backflow of blood from the ventricles to the atria.
Valves are also found in some veins of the body.
Work Step by Step
The aortic valves prevent blood from flowing from the aorta back to the left ventricle. The pulmonary valve prevents blood from flowing from the pulmonary artery back into the right ventricle.
The mitral and tricuspid valves prevent blood from the ventricles from flowing back into the atria when the ventricles contract.
Because veins oftentimes bring blood back to the heart against the force of gravity, veins contain valves that keep blood flowing in one direction toward the heart.
