You must have learnt about the circulatory system of the human body in your science class. A circulatory system is what is responsible for a systematic circulation of blood within our human body. Heart is the main organ which takes the sole responsibility of pumping blood into and out of the circulatory system. There are other helpers who carry blood from the heart to the other parts of the body. These helpers are classified as arteries and veins.
There are about 10 trillion cells within our body which are the reason behind the correct functioning of our body. From the stage of a new born till the last stage, these cells perform all functions to keep our body fit and healthy. There are simple cells, complex cells and even specialized cells that fight the aliens entering our body or aid in the growth of cut nails and many more trivial activities happening within the body without our very knowledge. In order to help these important cells survive and perform their duties, they need water, oxygen, fats and few minerals. The supply of oxygen is provided by the blood carriers – arteries and veins.
While the arteries carry oxygenated blood (pure blood) to all the body parts, veins carry the deoxygenated blood (impure blood) from the body parts. The cells utilize the oxygen from the blood to perform their tasks making the blood impure (deoxygenated).A study of these blood vessels is called Angiology. The appearance of veins in either blue or green shade is only because of the complicated optical system consisting of the light and skin. This has actually got nothing to do with the color of blood.