Which of the following describes a vein in the circulatory system?

The correct description of a vein in the circulatory system is that it is a blood vessel that returns blood to the heart. Veins serve a crucial function in the circulatory system by collecting deoxygenated blood from various parts of the body and carrying it back to the heart. This process is essential for maintaining proper circulation and ensuring that blood can be re-oxygenated in the lungs before being pumped out again to supply the body with oxygen-rich blood.

In contrast, arteries are responsible for carrying oxygenated blood away from the heart, thus differentiating the roles of these two types of blood vessels. Additionally, while some blood vessels may supply muscles with oxygen or carry nutrients, these descriptions refer to specific functions of arteries or capillaries, not veins. Understanding this distinction is vital for grasping the overall functionality of the circulatory system.