The primary function of the respiratory system is to transfer oxygen into the blood stream and carbon dioxide out. Oxygen is needed for cellular aerobic metabolism, and the removal of carbon dioxide is required to maintain acid-base balance. This is coordinated to maintain electrolyte and water balance in the face of changing metabolic requirements-sleep, activity, exercise, and food consumption. The respiratory System behaves like an ideal gas exchanger. It does this by providing the following functions:

• Provide a large contact area between air and blood (membrane allows diffusion and minimal resistance to gas £ow).