Lactic acidosis pathophysiology: Difference between revisions
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==Pathophysiology== | ==Pathophysiology== | ||
*[[Lactic Acidosis|Lactic acidosis]] occurs when cells make lactic acid faster than it can be metabolized. <ref>Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:77 ISBN 1591032016</ref> <ref>Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:68 ISBN 140510368X</ref> Both overproduction of lactate, or reduced metabolism, lead to acidosis. Normal lactate levels are less than | *[[Lactic Acidosis|Lactic acidosis]] occurs when cells make lactic acid faster than it can be metabolized. <ref>Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:77 ISBN 1591032016</ref> <ref>Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:68 ISBN 140510368X</ref> Both overproduction of lactate, or reduced metabolism, lead to acidosis. Normal lactate levels are less than 2 mmol/L, lactate levels between 2 mmol/L and 4 mmol/L are defined as hyperlactatemia. Severe hyperlactatemia is a level of 4 mmol/L or higher. | ||
*Other definitions for lactic acidosis include: pH less than or equal to 7.35 and lactatemia greater than 2 mmol/L with a partial pressure of carbon dioxide (PaC02) less than or equal to 42 mmHg. | |||
After glycolysis, pyruvate is shunted into two main pathways. Under aerobic conditions, it is converted to acetyl-CoA by pyruvate dehydrogenase, then enters the citric acid cycle and a series of reactions occur to form ATP (Adenosine Triphosphate) and NADH (nicotinamide adenine dinucleotide), which goes into oxidative phosphorylation, producing the majority of ATP in a cell. | |||
However, anaerobic conditions result in pyruvate channeling into the Cori cycle (lactic acid cycle), where pyruvate is converted to lactate, to regenerate NAD+ from NADH. The NAD+ generated can now be utilized in glycolysis again, forming two molecules of ATP per molecule of glucose. The lactate produced gets sent to the liver, for gluconeogenesis. | |||
Acid generation on the cellular level is dictated by the ratio of NAD+ and NADH. These molecules help maintain the intracellular pH by influencing the ratio of pyruvate to lactate. Therefore, an increased NADH concentration results in an increased lactate level. | |||
A marked increase in lactate production, in part due to catecholamine stimulation of glycolysis, also plays an important role in the lactic acidosis associated with shock, especially septic shock [9,10]. A similar mechanism explains the development of lactic acidosis when high doses of inhaled beta agonists are used to treat severe asthma [11]. | |||
Causes of increased NADH include a hypoxic state, ingestion and oxidation of large amounts of ethanol, etc. | |||
Lactic acidosis is an underlying process in the development of [[rigor mortis]]. Tissue in the muscles of the deceased resort to anaerobic metabolism in the absence of oxygen and significant amounts of lactic acid are released into the muscle tissue. This along with the loss of [[adenosine triphosphate|ATP]] causes the muscles to grow stiff. | Lactic acidosis is an underlying process in the development of [[rigor mortis]]. Tissue in the muscles of the deceased resort to anaerobic metabolism in the absence of oxygen and significant amounts of lactic acid are released into the muscle tissue. This along with the loss of [[adenosine triphosphate|ATP]] causes the muscles to grow stiff. | ||
==References== | ==References== | ||
{{Reflist|2}} | {{Reflist|2}} | ||
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Pathophysiology
- Lactic acidosis occurs when cells make lactic acid faster than it can be metabolized. [1] [2] Both overproduction of lactate, or reduced metabolism, lead to acidosis. Normal lactate levels are less than 2 mmol/L, lactate levels between 2 mmol/L and 4 mmol/L are defined as hyperlactatemia. Severe hyperlactatemia is a level of 4 mmol/L or higher.
- Other definitions for lactic acidosis include: pH less than or equal to 7.35 and lactatemia greater than 2 mmol/L with a partial pressure of carbon dioxide (PaC02) less than or equal to 42 mmHg.
After glycolysis, pyruvate is shunted into two main pathways. Under aerobic conditions, it is converted to acetyl-CoA by pyruvate dehydrogenase, then enters the citric acid cycle and a series of reactions occur to form ATP (Adenosine Triphosphate) and NADH (nicotinamide adenine dinucleotide), which goes into oxidative phosphorylation, producing the majority of ATP in a cell.
However, anaerobic conditions result in pyruvate channeling into the Cori cycle (lactic acid cycle), where pyruvate is converted to lactate, to regenerate NAD+ from NADH. The NAD+ generated can now be utilized in glycolysis again, forming two molecules of ATP per molecule of glucose. The lactate produced gets sent to the liver, for gluconeogenesis.
Acid generation on the cellular level is dictated by the ratio of NAD+ and NADH. These molecules help maintain the intracellular pH by influencing the ratio of pyruvate to lactate. Therefore, an increased NADH concentration results in an increased lactate level.
A marked increase in lactate production, in part due to catecholamine stimulation of glycolysis, also plays an important role in the lactic acidosis associated with shock, especially septic shock [9,10]. A similar mechanism explains the development of lactic acidosis when high doses of inhaled beta agonists are used to treat severe asthma [11].
Causes of increased NADH include a hypoxic state, ingestion and oxidation of large amounts of ethanol, etc.
Lactic acidosis is an underlying process in the development of rigor mortis. Tissue in the muscles of the deceased resort to anaerobic metabolism in the absence of oxygen and significant amounts of lactic acid are released into the muscle tissue. This along with the loss of ATP causes the muscles to grow stiff.