The respiratory system is made up of the organs that deliver oxygen to the circulatory system for transport to all body cells. Oxygen is essential for cells, which use this vital substance to liberate the energy needed for cellular activities. In addition to supplying oxygen, the respiratory system aids in removing of carbon dioxide, preventing the lethal buildup of this waste product in body tissues. Day-in and day-out, without the prompt of conscious thought, the …showed first 75 words of 955 total…

…showed last 75 words of 955 total…arranged in such a way that air in the wall of the alveoli is only about 0.1 to 0.2 microns from the blood in the capillary. Since the concentration of oxygen is much higher in the alveoli than in the capillaries, the oxygen diffuses from the alveoli to the capillaries. The oxygen flows through the capillaries to larger vessels, which carry the oxygenated blood to the heart, where it is pumped to the rest of the body.