The consumption of oxygen and the production of carbon dioxide are indispensable to life. The respiratory system is designed to exchange carbon dioxide and oxygen between the circulating blood and the atmosphere at a rate rapid enough for the body's needs, even during peak exercise.
The respiratory system starts at the nose and mouth and continues through the airways and lungs. The airways consist of the windpipe (trachea), which branches into the left and right bronchi, which lead to the two lungs. Each lung is divided into sections (lobes): three in the right lung and two in the left lung.