04 Dec Cellular Respiration
Respiration is the mechanism by which oxygen is supplied to the cells of our body and carbon dioxide is expelled. A gas exchange takes place in the alveoli when oxygen passes into the blood and carbon dioxide passes out of the blood. This exchange occurs because the gases in the air and blood have different concentrations and are separated by very thin capillary walls that surround the alveoli. When air is breathed into an alveolus, the oxygen is very concentrated and is diffused from the alveolar cavities into the capillaries where it is less concentrated and is transported through them to all the cells. Conversely, carbon dioxide diffuses in the opposite direction since it is much more concentrated in the alveolar capillaries than in the alveolar cavities. The oxygen is transported in plasma, and the small amount that is dissolved is mainly bound to hemoglobin. In the cells, or more precisely in the mitochondria, which are small organelles that serve as the powerhouse of the cells, the oxygen is used in the oxidation processes of glucose, which is produced from the digestion of food and in turn releases energy. Glucose is the source of energy for the human body, similar to the coal that fuels a boiler or the gas that powers a car engine. Glucose is oxidized in the reaction glucose + oxygen → carbon dioxide + water + energy. Too much carbon dioxide and water damage cellular activity so they must be removed from the cells through the blood and are transported to the alveoli where they are breathed out into the atmosphere.