Where do veins come from?

Veins originate from venules, which are small blood vessels that collect deoxygenated blood from tissue capillaries. Venules converge to form larger veins, which carry the blood back to the heart. The largest veins in the body are the superior vena cava, which carries blood from the upper body, and the inferior vena cava, which carries blood from the lower body. These two veins empty into the right atrium of the heart.