Lactic acid from muscle contraction

The above observations suggested that hexoses arise in Nature by reaction of glycerose with dihydroxyacetone. A vast amount of practical information has been derived from investigation of plant- and muscle-extracts, two dissimilar systems that show many similarities in their biosynthetic manipulations. There is a close parallelism in the sequence of intermediates involved in the processes wherein D-glucose is converted to ethanol and carbon dioxide by yeasts, and to lactic acid by muscle during contraction. The importance of these schemes lies in their reversibility, which provides a means of biosynthesis from small molecules. 

The lactate formed by active skeletal muscles (or by erythrocytes) can be recycled it is carried in the blood to the liver, where it is converted to glucose during the recovery from strenuous muscular activity. When lactate is produced in large quantities during vigorous muscle contraction (during a sprint, for example), the acidification that results from ionization of lactic acid in muscle and blood limits the period of vigorous activity. The best-conditioned athletes can sprint at top speed for no more than a minute (Box 14-1). 

He worked on the sources of energy for muscular contraction, a continuation of his first interest in muscle creatine. Phosphagen had been recently discovered. Einar Lundsgaard had just shown that muscle poisoned with iodoacetic acid was able to perform a certain amount of work without liberation of lactic acid. Using muscles with low carbohydrate content, Ochoa was able to demonstrate the muscle s ability to perform work using sources of energy different from those then known. It was an important piece of work on a topic of great interest at the time. 

Fletcher and Hopkins showed that lactic acid is formed quantitatively from glucose during anaerobic muscle contraction. 

The cause of the pain is unknown, although there are many hypotheses such as damage to muscle (43,44) resulting from asynchronous contractions of adjacent muscle fibers (45), irreversible damage to muscle spindles (46), potassium flux (47), lactic acid (48), serotonin (49), calcium influx-associated damage to muscle spindles (50), and prostaglandins (51,52). The pain appears not to be related to the extent or intensity of the observed fasciculations. 

The accumulation of lactate is often cited as a cause of fatigue during intense muscle contraction but the effect is actually due to a low pH in muscles. Protons dissociate in a reversible manner from lactic acid, glycolytic intermediates, and the purine nucleotides, thus contributing to a net increase of protons in solution. A marked drop in pH is not conducive to efficient operation of the contractile machinery, as well as inhibiting hexokinase and phosphofructokinase in glycolysis. 

Ruhenstroth-Bauer 1975). This phenomenon causes the increase of R.. The resistive element Re that represents extracellular fluids decreases over time with AR. (LD) = 331.93 Q and AR. (RA) = 455.54 D. At slaughter, the animal muscles contract due to the release of lactic acid contained in muscle fibers, by releasing the muscle fibers, lactic acid activates the inert enzymes already present in the muscle, which will be gradually cut the muscle fibers. Besides the release of electrolytes from cells to the extracellular tissue, these two phenomena cause the increase of conductivity and proportionally the decrease of R. ... 

Meyerhof, Otto Friti (1884-1951) German-born American biochemist whose work on muscle physiology showed that lactic acid was produced from muscle glycogen during muscle contraction in anaerobic conditions. He also showed that the utilization of glucose as a fuel in living cells involved a cyclic biochemical pathway. For these discoveries, he received the Nobel Prize in physiology or medicine in 1922. 

When a person exercises, muscle contractions produce lactic acid. Moderate increases in lactic acid can be bandied by tbe blood buffers without decreasing the pH of blood. However, excessive amounts of lactic acid can overload tbe blood buffer system, resulting in a lowering of the blood pH. A condition called acidosis is diagnosed if the blood pH falls to 7.35 or lower. Assume the primary blood buffer system is the carbonate buffer system described in Exercise 45. Calculate what happens to the [H2C03]/[HC03 ] ratio in blood when the pH decreases from 7.40 to 7.35. 

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