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Cori cycle. The Cori cycle (also known as the lactic acid cycle), named after its discoverers, Carl Ferdinand Cori and Gerty Cori, [1] is a metabolic pathway in which lactate, produced by anaerobic glycolysis in muscles, is transported to the liver and converted to glucose, which then returns to the muscles and is cyclically metabolized back to lactate.
Lactic acid fermentation is a metabolic process by which glucose or other six-carbon sugars (also, disaccharides of six-carbon sugars, e.g. sucrose or lactose) are converted into cellular energy and the metabolite lactate, which is lactic acid in solution.
As a result, they rely on lactic acid fermentation to provide the majority of their energy needs. [23] Adaptations in particular in the turtle's blood composition and shell allow it to tolerate high levels of lactic acid accumulation. In the anoxic conditions where fermentation is dominant, calcium levels in the blood plasma increase. [23]
Pyruvate is the terminal electron acceptor in lactic acid fermentation. When sufficient oxygen is not present in the muscle cells for further oxidation of pyruvate and NADH produced in glycolysis, NAD+ is regenerated from NADH by reduction of pyruvate to lactate. [4] Lactate is converted to pyruvate by the enzyme lactate dehydrogenase. [3]
Lactic acid tends to accumulate in the muscles, which causes pain in the muscle and joint as well as fatigue. [13] It also creates a gradient which induces water to flow out of cells and increases blood pressure. [14] Research suggests that lactic acid may also play a role in lowering levels of potassium in the blood. [15]
In addition to Cori Cycle, the lactate shuttle hypothesis proposes complementary functions of lactate in multiple tissues. Contrary to the long-held belief that lactate is formed as a result of oxygen-limited metabolism, substantial evidence exists that suggests lactate is formed under both aerobic and anaerobic conditions, as a result of substrate supply and equilibrium dynamics.
Characteristic features include developmental delay and a buildup of lactic acid in the blood (lactic acidosis). Increased acidity in the blood can lead to vomiting, abdominal pain, extreme tiredness , muscle weakness, and difficulty breathing. In some cases, episodes of lactic acidosis are triggered by an illness or periods without food.
It was once believed that lactic acid build-up was the cause of muscle fatigue. [8] The assumption was lactic acid had a "pickling" effect on muscles, inhibiting their ability to contract. Though the impact of lactic acid on performance is now uncertain, it may assist or hinder muscle fatigue.