An externality is defined as a benefit or cost that is imposed on a third party, such as society, other than the producer or consumer of a good or service, or, more simply, an economic side effect. The more of a product that is consumed or produced, the more of an externality that results.
Arteries carry oxygenated blood (with the exception of the pulmonary artery and umbilical artery). Veins carry deoxygenated blood (with the exception of pulmonary veins and umbilical vein).
The structural differences between arteries and veins are all based in their relationship to the heart. Since arteries receive blood from the heart, the blood they receive is under a lot of pressure. intend to explore the structure and function of arteries, veins and capillaries. When an artery branches into smaller and smaller vessels, eventually the blood vessel is too small to see with the naked eye. At that point, it is called an arteriole. Likewise, a venule is a microscopic vein.