Respiratory System in Living Organisms
Respiration is a necessary physiological process in all living organisms by which they obtain energy for carrying out all the metabolic activities of the body. The word respiration has several meanings. In Latin, from which it has been derived, the meaning of it is 'to breathe' or 'to exhale' and in this sense, respiration was basically applied to the exchange of gases between an organism and its environment. It meant the activities of breathing or their equivalent. As years rolled by, it became apparent that the basic exchanges occurred at the cellular level and consequently the term internal respiration was applied to this phase of gaseous exchange. The exchange of gases among the body surface and the environment then came to be called external respiration. This division is quite helpful even today. Now days however, respiration is frequently referred to the cellular processes included in energy production that is the chemical processes occurring in the cell to liberate energy. We are here concerned with external respiration and transport of gases among tissues and the respiratory site.