Final answer:
Veins with a diameter of up to about 10 mm that have valves to prevent backflow are referred to as large veins. These veins have large lumens, thin walls, and rely on muscle contractions and valves to move blood toward the heart.
Step-by-step explanation:
The veins that are up to about 10 mm in diameter and are equipped with valves to prevent the backflow of blood are called large veins. These veins have thin walls, large and irregular lumens, and operate under low blood pressure. Larger veins include the superior and inferior venae cavae, and they utilize the contraction of surrounding skeletal muscles and the presence of valves to move blood back toward the heart. While smaller veins and venules may lack these valves, larger veins consistently possess them to ensure the unidirectional flow of blood.