Mechanism of Development in Hypoxia
The fundamental cause of lactic acid accumulation lies in impaired oxygen supply to peripheral tissues (hypoxia). Life-threatening conditions such as myocardial infarction, pulmonary embolism, or massive hemorrhage deprive cells of an adequate oxygen supply.
In response to oxygen deprivation, cells must reprogram their energy metabolism. To meet basic energy demands, they urgently upregulate anaerobic glycolysis—the breakdown of carbohydrates without oxygen. The byproduct of this emergency pathway is lactic acid. As a result, blood lactate levels spike sharply, and plasma pH drops below optimal values. This acidic environment is detrimental to most protein structures, disrupting the spatial conformation of enzymes and ultimately leading to global cellular metabolism failure.
Metabolic Clearance of Lactate
In a healthy body, the concentration of lactic acid is strictly controlled by the balance between its continuous production and removal rate (clearance). Lactate utilization occurs via two main physiological pathways:
- Aerobic oxidation. In the presence of sufficient oxygen, molecules are broken down into end products—carbon dioxide ($CO_2$) and water ($H_2O$).
- Gluconeogenesis. Lactate serves as a vital plastic substrate for synthesizing new glucose molecules. This process predominantly takes place in liver tissue and is a key link in the Cori cycle.
Enzymatic and Organ-Specific Causes of Imbalance
Lactic acidosis manifests when the pyruvate and lactate disposal mechanisms break down. In addition to tissue hypoxia and dystrophy that stimulate excessive acid production, internal enzymatic and organ defects play a massive role:
- Hepatocyte pathology. Any major loss of liver tissue (e.g., cirrhosis or severe toxic hepatitis) deprives the organ of its ability to efficiently extract lactate from the blood and convert it into glucose.
- Pyruvate dehydrogenase complex (PDH) dysfunction. This multienzyme complex is responsible for converting pyruvate to acetyl-CoA. If PDH is blocked due to inherited mutations or severe hypovitaminosis (specifically, vitamin B1 deficiency), aerobic oxidation halts. Excess pyruvate inevitably converts into lactate.
- Defects in gluconeogenesis enzymes. Inherited protein abnormalities responsible for glucose synthesis make it impossible to use lactic acid as a building block.
- Citric acid cycle enzyme blockade. Reduced activity of Krebs cycle (TCA cycle) enzymes also interrupts the aerobic oxidation pathway, shifting the reaction equilibrium toward tissue acidification.