Definition of lactic acid
During fermentation, lactate dehydrogenase converts pyruvate to L-lactate. In general Metabolism and movement of lactic acid are constantly produced, but its concentration is generally not increased. Only in the lactic acid production process to accelerate, lactic acid can not be transported away in time will increase its concentration. Lactic acid transport speed is affected by a number of factors, including monocarboxylate transporter, lactate dehydrogenase concentration and isomeric form, the oxidation capacity of the organization. In general the concentration of lactic acid in the blood is not moving 1-2mmol/L, in strong exercise can rise to 20mmol/L.
In general, the concentration of lactic acid increases when the energy of the tissue can not be met by aerobic respiration, the tissue is unable to obtain sufficient oxygen or the oxygen can not be processed quickly enough. In this case pyruvate dehydrogenase can not be timely pyruvate to acetyl-CoA, pyruvate began to accumulate. In this case, if lactate dehydrogenase does not reduce pyruvate to lactate, the glycolysis process and adenosine triphosphate synthesis are inhibited. The process of producing lactic acid: pyruvate+NADH+H→lactate+NAD+2H
The significance of this process is to reconstruct the nicotinamide adenine dinucleotide (NAD+) required for glycolysis to maintain adenosine triphosphate synthesis. In oxygen-rich muscle cells, lactic acid can be oxidized to pyruvate and then directly used as a fuel for the tricarboxylic acid cycle. It can also be converted to glucose via the Krebs cycle during gluconeogenesis in the liver. Lactobacillus bacteria can also be lactic acid fermentation. These bacteria can live in the mouth, they produce lactic acid is the cause of dental caries. In medicine, lactic acid is often used in lactated Ringer's solution. This is a solution of sodium chloride, potassium chloride and lactic acid in distilled water isotonic with human blood. In the injury, surgery or burns often after the loss of blood using lactated Ringer's fluid to supplement blood loss.
Physicochemical properties of lactic acid
Pure product is colorless liquid, industrial colorless to light yellow liquid. Odorless, with hygroscopicity. The relative density of 1.2060 (25/4°C). The temperature of 18°C. The boiling point of 122°C (2kPa). Refractive index nD (20°C) 1.4392. With water, ethanol, glycerol immiscible, acidic aqueous solution, PKa=3.85. Do not dissolve in chloroform, carbon disulfide and petroleum ether. Under normal pressure heating decomposition, concentrated to 50%, the part into lactic anhydride, so the product often contains 10% to 15% of lactic anhydride. With the hydroxyl and carboxyl, under certain conditions, can occur esterification reaction, there are three products.
Toxicity: rat oral LD50 is 3.73g/kg body weight; ADI no restrictions. Lactic acid has two isomers: D-type and L-type. The rats were divided into three groups, the DL-type, D-type, and L-type lactic acid of 1.7 g/kg body weight were administered for each group. After three hours of oral administration, DL-lactic acid increased liver glycogen , 40% to 95% in the 3h absorption transformation; D-and L-type lactate increased blood lactate from the urine excreted.
Relationship between human and lactic acid
For the human body, lactic acid is one of the fatigue substances, the body in maintaining body temperature and body movement generated heat generated during the waste. Most of the energy we need to survive our bodies comes from sugar. Blood glucose as needed to send to various organs of combustion, produce heat. This process will produce water, carbon dioxide and pyruvate, pyruvate and hydrogen combined to produce lactic acid. If the body's energy metabolism can be normal, will not produce accumulation, will be brought to the liver blood, and further decomposition of water and carbon dioxide, heat, fatigue is eliminated.
If the movement is too intense or lasting, or the body decomposition of lactic acid necessary for the lack of vitamins and minerals, then the body of lactic acid too late to be processed, resulting in the accumulation of lactic acid. Too much lactic acidity will be weak alkaline body fluids, affecting the smooth absorption of nutrients and oxygen cells, weakening the normal function of cells. The accumulation of lactic acid muscle contraction occurs, thus squeezing the blood vessels, making poor blood flow, resulting in muscle soreness, chills, headache, head weight and so on. Lactic acid accumulation in the early cause soreness and fatigue, if ignored for a long time, causing physical acidification, may cause serious illness.
Some people use to sleep on the holiday to eliminate fatigue, which is invalid. With chemicals can only be temporary relief, but also side effects. The correct way is to use appropriate exercise, especially the relaxation exercises to relax the muscles and promote blood circulation, choose a balanced light nutrition, especially food rich in vitamin B family, coupled with high-quality sleep, it will get the best Effect.
In the process of intense exercise the human body needs a lot of energy. At this time the production of lactic acid in the body than the organization to remove lactic acid is high, the organization of lactic acid concentration. The significance of this process is to reconstruct the nicotinamide adenine dinucleotide (NAD) required for glycolysis to maintain adenosine triphosphate production and to provide a constant source of energy for exercise. This process can be described as: pyruvate+NADH+H→Lactate+NAD
Unlike the general description of the wrong increase in lactic acid concentration itself does not lead to acidosis, it is not the reason muscle soreness. Lactic acid in the human body can not release protons, so there is no acid. Analysis of the glycolytic pathway in humans has shown that this process does not lead to acidosis. There is another reason for the acidosis caused by intense exercise.
The adenosine triphosphate is hydrolyzed to release energy which is released by a proton. These protons are the cause of acidosis. In the strong exercise aerobic metabolism can not guarantee the production of adenosine triphosphate, so anaerobic metabolism began. But the energy generated is not enough to all the ADP into ATP, and a large number of ATP hydrolysis of ADP and proton, resulting in ADP and proton increase. This is one of the many reasons muscle soreness during intense exercise. Some people think that through the strong ion concentration gradient lactic acid can cause acidosis, but the study of this process is also very imperfect, so whether it is still unclear.