Respiration is frequently confused with the process of breathing. Respiration is in fact concerned with the liberation of energy, which is so vital to the body. Whilst breathing is the process of filling and emptying the lungs to bring air into contact with the blood. Energy is obtained from food which contains complex chemicals, such as glucose. The glucose molecule contains atoms of carbon, hydrogen and oxygen held together by chemical bonds. Energy is required for the formation of these chemical bonds and when broken energy is released.
RESPIRATION IS AN OXIDATION PROCESS, which occurs in a living cell. Oxygen is usually necessary for the process. Oxygen we need to oxidise glucose in the body cells is obtained from the air during breathing. This rhythmic process normally takes place about sixteen to seventeen times a minute. Air is forced through the air passage in the head and so into the lungs by atmospheric pressure when the chest increases in volume. This increase is brought about by the lowering of the diaphragm due to the contractions of the diaphragm muscles and by the upward and outward movement of the ribs due to the contraction of the intercostal muscles between the ribs. The air in the lungs is forced out of the body, when the volume of the chest decreases, due to the relaxation of the diaphragm muscles. So raising the diaphragm and the relaxation of the intercostal muscles which lowers the ribs.
The alternate contraction and relaxation of these muscles is controlled by messages from the brain, sent along nerves to the muscles. The lungs themselves contain a series of finely branching tubes each ending in a small group of air sacs called ALVEOLI. The walls of the air sacs are very thin and are surrounded by a network of fine blood capillaries. It is here that oxygen from the air in the lungs passes through the alveoli walls into the blood. At the same time carbon dioxide, the waste product of the oxidation of glucose in the body cells passes from the bloodstream into the air sacs and breathed out. The exchange of gasses in the lungs is called EXTERNAL RESPIRATION. Thus the air breathed out contains more carbon dioxide and less oxygen than the air breathed.
