Where do veins carry blood?

Veins are blood vessels that are primarily responsible for carrying blood back to the heart. This function is crucial for maintaining proper circulation within the body. After oxygen and nutrients have been delivered to tissues and organs via arteries, the veins collect the deoxygenated blood or blood that has delivered its nutrients and transport it back to the heart. This process is essential for allowing the heart to reoxygenate the blood in the lungs and pump it out again to the rest of the body, ensuring that the circulatory system functions effectively.

The role of veins is particularly highlighted in the context of systemic and pulmonary circulation; for example, in the pulmonary circuit, veins carry oxygenated blood from the lungs back to the heart. Thus, the correct answer reflects the primary function of veins in the circulatory system: to return blood to the heart.