The major organs of the respiratory system are the lungs, trachea, bronchi and diaphragm. The respiratory system works together with the cardiovascular system to deliver oxygen to the organs and with the autonomic nervous system to regulate breathing.
The lungs are the main organ of the respiratory system, which carries oxygen through the body by means of red blood cells and picks up carbon dioxide, a waste gas, to expel from the body when an organism exhales. The trachea filters the inhaled air and branches into the bronchi, where the air tubes carry air directly into the lungs. The diaphragm is the main muscle of the respiratory system, contracting to increase the volume of the lungs and carry air into the body and expanding to force air out of the lungs.