Lactic Acid

Examples of Lactic Acid in the following topics:

• Muscle Fatigue

  • Pyruvate is continually processed into lactic acid.
  • With pyruvate accumulation, lactic acid production is also increased.
  • This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising.
  • Lactic acid is transported to the liver where it can be stored prior to conversion to glucose in the presence of oxygen via the Cori Cycle.
  • The amount of oxygen required to restore the lactic acid balance is often referred to as the oxygen debt.

• Muscle Metabolism

  • Pyruvate is continually processed into lactic acid.
  • With pyruvate accumulation, the amount of lactic acid produced is also increased.
  • This lactic acid accumulation in the muscle tissue reduces the pH, making it more acidic and producing the stinging feeling in muscles when exercising.
  • While the pyruvate generated through glycolysis can accumulate to form lactic acid, it can also be used to generate further molecules of ATP.
  • Cellular respiration is limited by oxygen availability, so lactic acid can still build up if pyruvate in the Krebs Cycle is insufficient.

• Impacts of Exercise on Muscles

  • In the short term muscle can become fatigued and sore for reasons like impaired blood flow, ion imbalance within the muscle, nervous fatigue, loss of desire to continue exercising, and most importantly, the accumulation of lactic acid in the muscle.
  • Muscle soreness, once thought to be due to lactic acid accumulation, has more recently been attributed to small tearing, or micro-trauma, of the muscles fibers caused by eccentric contraction.

• Internal Respiration

  • Cellular respiration can occur anaerobically without oxygen, such as through lactic acid fermentation.
  • Human cells may use lactic acid fermentation in muscle tissue during strenuous exercise when there isn't enough oxygen to power the tissues.
  • A diagram of cellular respiration including glycolysis, the Krebs cycle (also called the citric acid cycle), and the electron transport chain.

• Blood Flow in the Brain

  • The arteries deliver oxygenated blood, glucose and other nutrients to the brain and the veins carry deoxygenated blood back to the heart, removing carbon dioxide, lactic acid, and other metabolic products.

• Adjustments During Exercise

  • This can cause a buildup of lactic acid in the muscles, which is the byproduct of lactic acid fermentation (the most common anaerobic respiration process in the human body).
  • This is one reason why muscles may become sore during exercise, though the lactic acid is eventually removed through conversion to glucose in the liver.

• Dental Caries

  • The mineral content of teeth is sensitive to increases in acidity from the production of lactic acid.
  • Most foods are in this acidic range and without remineralization result in the ensuing decay.
  • All caries occur from acid demineralization that exceeds saliva and fluoride remineralization, and almost all acid demineralization occurs where food (containing carbohydrate like sugar) is left on teeth.
  • These minerals, especially hydroxyapatite, will become soluble when exposed to acidic environments.
  • Bacteria in a person's mouth convert glucose, fructose, and most commonly sucrose (table sugar) into acids such as lactic acid through a glycolytic process called fermentation.

• Semen

  • The seminal vesicles produce a yellowish viscous fluid rich in fructose, amino acids, and other substances that makes up about 70% of human semen.
  • The prostatic secretion, influenced by dihydrotestosterone, is a whitish (sometimes clear), thin fluid containing proteolytic enzymes, citric acid, acid phosphatase, and lipids.
  • The normal environment of the vagina is a hostile one for sperm cells, as it is very acidic (from the native microflora producing lactic acid), viscous, and patrolled by immune cells.
  • These alkaline bases counteract the acidic environment of the vaginal canal and protect DNA inside the sperm from acidic denaturation.

• Energy Requirements

  • The heart derives energy from aerobic metabolism via many different types of nutrients. 60% of the energy to power the heart is derived from fat (free fatty acids and triglycerides), 35% from carbohydrates, and 5% from amino acids and ketone bodies from proteins.
  • Lactate, created from lactic acid fermentation, accounts for the anaerobic component of cardiac metabolism.
  • The produced pyruvate can then be burned aerobically in the citric acid cycle (also known as the tricarboxylic acid cycle or Krebs cycle), liberating a significant amount of energy.

• Acidosis

  • Acidosis describes increased acidity in the blood and other tissues, usually measured as arterial pH below 7.35.
  • If not further qualified, it usually refers to acidity of the blood plasma.
  • Metabolic acidosis may result from increased production of metabolic acids or disturbances in the ability to excrete acid via the kidneys.
  • Another example of increased production of acids occurs in starvation and diabetic acidosis.
  • In hypovolemic shock for example, approximately 50% of the metabolic acid accumulation is lactic acid, which disappears as blood flow and oxygen debt are corrected.