The blood stream is refered to in essence as the continuos stream of blood which flows and is pumped around your body. Your blood stream carries substances vital for daily processes. Pumped around by your cardiovascular system i.e. your heart, your blood stream carries substance such as hormones, red blood cells, white blood cells and waste products etc. The waste products such as urea, uric acid and carbondioxide are transported to their appropriate organis in the body to then be excreted. The blood stream is also involved in regulating the body's temperature and pH. It is able to maintain a constant body temperature through the blood vessels. If the body is too warm for example, the blood vessels widen and there is a larger blood flow towards the inner surface of the skin thus giving off heat to the external enviroment.