CO2
Carbon dioxide is essential for internal respiration in a human body. Internal respiration is a process, by which oxygen is transported to body tissues and carbon dioxide is carried away from them. Carbon dioxide is the wast that your respiration suppose to release after you inhale Oxygen, it can be so dangerous for your body if it build up in your cells.
The major buffers system in blood is the sodium bicarbonate-carbonid acid system. This system is major importance because both components in buffer system present a larg amounts and the concentrations of these two components are regulated and maintained by body's certain organs. The concentration of carbonic acid (dissolved carbon dioxide) is controlled by lung and the concentration of bicarbonate is controlled by kidney.

gasexch_2.gif
Detail of gases exchange in Lung

2009, Homeostasis, [Internet]http://knowledgerush.com/kr/encyclopedia/Homeostasis/. Retrieved April 14th, 2009

2004, Lenntech Carbon dioxide , [internet]://www.lenntech.com/carbon-dioxide.htm. Retrieved April 14th, 2009