Respiration
From Halbeeg, the open encyclopedia · Af-Soomaali
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Respiration is the process by which living organisms obtain oxygen and expel carbon dioxide. The term has two related meanings: one refers to the mechanical movement of air in and out of the body, and the other refers to the chemical reactions that occur within cells to produce energy from food.
Most organisms require oxygen to break down sugars and fats and convert them into energy. This process is called cellular respiration. It produces energy (ATP), water, and carbon dioxide, which the body then expels.
Distinction of terms
External respiration is the exchange of gases between the body and the environment—through the lungs of humans, gills of fish, or spiracles of insects. Internal respiration is the transfer of gases between blood and cells. Cellular respiration is the biochemical reaction that occurs inside the cell, particularly in the part called the mitochondrion.
The human system
During breathing, the diaphragm and muscles between the ribs pull air into the lungs. Air passes through the nose or mouth, then the throat, windpipe (trachea), and bronchial branches, until it reaches small air sacs called alveoli. There oxygen passes into the blood through tiny blood vessels, while carbon dioxide passes out. Oxygen is carried by hemoglobin in red blood cells.
Breathing is controlled by nerve centers in the brainstem, which are highly sensitive to carbon dioxide and acid levels in the blood. Therefore, as the body works harder, breathing increases automatically without conscious decision.
Variation among organisms
Small organisms such as bacteria and microorganisms exchange gases directly across their cell membranes. Fish use gills (gills) to extract oxygen from water. Insects have a system of tubes called tracheae that deliver air directly to cells. Plants use oxygen in cellular respiration and also produce oxygen during photosynthesis.
There is also a form of respiration that does not use oxygen, called anaerobic respiration. For example, human muscles under low oxygen produce lactic acid, while some bacteria and yeast use fermentation to obtain energy.