What is the primary function of veins in the circulatory system?

The primary function of veins in the circulatory system is to carry oxygen-depleted blood toward the heart. After the oxygen has been delivered to the tissues and organs throughout the body, the blood returns to the heart through veins. This blood is typically low in oxygen and high in carbon dioxide, making it vital for veins to transport this blood to the heart, where it can be sent to the lungs for oxygenation.

Veins have a unique structure that includes valves to prevent the backflow of blood, ensuring that it moves steadily toward the heart under relatively low pressure. The distinction between veins and arteries is crucial in understanding their specific roles in circulation—arteries carry oxygen-rich blood away from the heart, while veins return the depleted blood for re-oxygenation.

While the other options mention important processes related to blood flow or functions of the circulatory system, they do not accurately describe the primary role of veins. For instance, veins do not transport nutrients directly, which is mainly a function of blood vessels called capillaries in conjunction with arteries. Moreover, while veins contribute to blood pressure regulation to some extent, their main job is the collection of blood and its return to the heart.