What characteristic cannot be applied to veins?

Veins are blood vessels responsible for carrying blood back to the heart. One of their defining characteristics is that they always carry blood toward the heart, which contrasts with arteries that transport blood away from the heart.

The presence of thick muscular walls is typically associated with arteries, which need to withstand higher pressure from the blood being pumped directly from the heart. Veins, on the other hand, have thinner walls and often contain valves that help prevent the backflow of blood as it returns to the heart, especially from the lower extremities where the force of gravity is a concern.

By identifying that veins cannot carry blood away from the heart, it becomes clear that this characteristic does not apply to them. This understanding is essential for distinguishing between the different types of blood vessels and their functions within the circulatory system.