The main function of the respiratory system is the exchange of gases such as oxygen and carbon dioxide in the lungs. Breathing, or respiration, allows this important function to take place. Air carrying oxygen enters the body during inhalation, and air carrying carbon dioxide is expelled out of the body through exhalation. Oxygen is a vital requirement of all cells in order to survive and perform their many functions. Carbon dioxide is mostly a waste product of processes inside the body and is not usually needed by cells.
All structures in the respiratory tract play necessary roles in the function of the system. The upper respiratory tract, which includes the nose, throat, voice box, and trachea or windpipe, are passageways for oxygen and carbon dioxide during the breathing process. In the lower respiratory tract, comprised of the lungs, bronchi, and alveolar sacs, the process of gas exchange takes place.
As oxygen reaches the trachea, it travels to the two main bronchi, which divide into the right lung and the left lung. Oxygen then proceeds to numerous bronchioles of each lung, and finally down to the millions of alveolar sacs. Smaller blood vessels, called capillaries, are present in the surfaces of the alveolar sacs. Blood carrying carbon dioxide travels to the lungs through the capillaries to exchange that gas for oxygen. Oxygen-carrying blood then goes to the heart to be delivered to other organs of the body.
The breathing process is governed by the actions of the central nervous system, the diaphragm, the lungs, and the circulatory system. There is a respiratory center in the brain that regulates the process. Muscles in the chest, like the diaphragm and those between the ribs, help in the expansion and collapse of the lungs during each breath. After the exchange of gases in the lungs, oxygenated blood usually enters the circulatory system to reach all parts of the body.
Any disturbance in the components that regulate the breathing process can affect the function of the respiratory system. Diseases of the respiratory tract can include infections like pneumonia, tuberculosis, and bronchitis. Narrowing of the airways often makes breathing difficult for many asthma patients. Harmful substances, like tobacco smoke and radon gas, can also reach the lungs if they are inhaled from the air. These substances can lead to the development of lung tumors and cancers, often causing deterioration of the respiratory system and other systems of the human body.