Is carbon dioxide really a waste product? The metabolism of living organisms can be divided into anabolism and anabolism. The process of acquiring substances from the outside world and converting them into new substances in the body is called assimilation, and the process of converting old substances in the body into substances in the environment is called anabolism. Both assimilation and anisotropy involve a series of intermediate metabolic reactions. Tricarboxylic acid cycle The tricarboxylic acid cycle is the central link between the aerobic metabolism of substances, which organically connects sugar metabolism, lipid metabolism and protein metabolism. The tricarboxylic acid cycle releases carbon dioxide, and the hydrogen (2H) that is shed is oxidatively phosphorylated to form water and 2-3 molecules of ATP energy, and so on and so forth. Whether the sugary food we ingest is grain, starch or whatever sugar, it must be turned into monosaccharides such as glucose, fructose and galactose in the small intestine before it can be absorbed. The monosaccharides such as mannose, fructose and galactose that are digested and absorbed are all readily converted to glucose by the liver. The tricarboxylic acid cycle allows the complete oxidation of sugars and the storage of energy in the form of ATP. The tricarboxylic acid cycle takes place in the mitochondria of hepatocytes under aerobic conditions; in other words, carbon dioxide is produced by cellular metabolism in the body. Under anaerobic conditions, sugar can also be metabolized (called sugar anaerobic catabolism or glycolysis), but the site of metabolism is mainly in the muscle. Glycolysis also produces cotton, and the pyruvate produced after glycolysis can also enter the tricarboxylic acid cycle under aerobic conditions and be oxidized and decomposed into carbon dioxide and water, which also stores large amounts of energy in the form of ATP. The human body can produce 300-400ml of carbon dioxide every day, which must be excreted through continuous breathing. Carbon dioxide enters the bloodstream and combines with water to form carbonic acid, which rapidly decomposes into hydrogen ions and bicarbonate ions. When the concentration of hydrogen ions increases, it causes acidosis. In this sense, carbon dioxide is a waste product and must be excreted from the body. Carbon dioxide is still indispensable to the human body because it is an important stimulus for the normal activity of the respiratory center, and its stimulating effect on respiration is achieved through peripheral chemoreceptors. Carbon dioxide diffuses from the cerebral vasculature into the cerebrospinal fluid and quickly combines with water and releases hydrogen ions, which stimulate the central chemoreceptors and participate in the regulation of respiration, and the stimulatory effect of hydrogen ions may be more important than carbon dioxide itself. A portion of carbon dioxide is also present in the residual air in the alveolar cavity. It also plays a role in maintaining alveolar tone and avoiding alveolar atrophy. From this point of view, carbon dioxide is not a waste product. We cannot hope that the less carbon dioxide in the arterial blood or in the alveoli will be better, too little and respiratory alkalosis will develop, which is equally bad for the organism. The problem is that the partial pressure of carbon dioxide in the arterial blood and alveoli must be kept constant at normal levels, and therefore the airway must be kept unobstructed.