A colorless gas produced by the complete oxidation of organic compounds through the release of energy. Carbon dioxide is the endproduct when CARBOHYDRATE, PROTEIN, and FATS are completely burned by the body to produce energy (respiration). This gas readily diffuses out of the cells where it is produced, dissolves in blood, and is transported to the lungs. There, carbon dioxide migrates out into air, contained in the lungs, while oxygen diffuses into the blood to replace that used in respiration. The distance between blood and air at the lung tissue lining is exceedingly small, only 0.0001 cm too small to slow gas exchange. Shallow breathing and lung diseases lead to excessive carbon dioxide buildup, which can create acidic conditions (ACIDOSIS).
Carbon dioxide in the blood is more than a waste product. It combines with water to form CARBONIC ACID, which breaks down to BICARBONATE, a major pH BUFFER to neutralize acids. The kidney also forms bicarbonate to help maintain the acid-base balance.
Industrial Uses of Carbon Dioxide
Carbonated beverages contain carbon dioxide maintained under pressure. Carbon dioxide is responsible for the bubbles in BEER, mineral water, and SOFT DRINKS and contributes to their slightly sour (acidic) taste. Carbon dioxide is used as a refrigerant (dry ice), a foaming agent, and as a growth promoter of plants in greenhouses.