ANATOMY

Detailed explanation-1: -Unlike arteries, veins contain valves that ensure blood flows in only one direction. (Arteries don’t require valves because pressure from the heart is so strong that blood is only able to flow in one direction.) Valves also help blood travel back to the heart against the force of gravity.

Detailed explanation-2: -Medium and large veins have venous valves, similar to the semilunar valves associated with the heart, that help keep the blood flowing toward the heart. Venous valves are especially important in the arms and legs, where they prevent the backflow of blood in response to the pull of gravity.

Detailed explanation-3: -Arteries can maintain that high blood pressure due to their strong lining and flexible walls that allow for the additional push of blood. Because of this unique design and the assistance they receive from the heart, they do not need valves to prevent backflow.

Detailed explanation-4: -The valveless veins are veins that lack venous valves. Most veins contain valves (known as the valvula venosa in the TA) to prevent backflow, i.e. ensuring that blood flow is always towards the heart 1.