What is the primary function of veins?

The primary function of veins is to carry deoxygenated blood back to the heart. This is crucial to the circulatory system because veins collect blood that has circulated through the body, delivering nutrients and oxygen to tissues, and then return it to the heart, where it can be pumped to the lungs for oxygenation.

In this process, veins have thin walls and valves that prevent the backflow of blood, which helps maintain the unidirectional flow toward the heart. This function is essential for maintaining an adequate circulation of blood, ensuring that it can be re-oxygenated and circulated again.

Other options do not accurately describe the primary role of veins. For example, arteries are responsible for transporting oxygenated blood away from the heart, while the filtering of blood occurs in the kidneys, and hormone dissemination is primarily managed by the endocrine system. Thus, the role of veins is specifically linked to returning deoxygenated blood to the heart, making this the correct choice.