Tiny capillaries gather and enlarge as they proceed into tributaries.
In their combined effort they pour blood that has been in circulation back to the heart. The veins wear coats much like the arteries, their coats are thinner and many are transparent. The function they perform is cooperative not competitive. These little vital pathways are the best example of an unified effort engaged in providing life so the being can thrive. In the blueprint of the organism, compatible structures that utilize varied systems exist not in consequence of each other.