Anaerobic Metabolism

Describe the consequences of anaerobic metabolism and ketone production

Lactate

The Embden-Meyerhof pathway:

  • Describes the conversion of glucose to pyruvate (and two ATP)
  • Does not consume O2 or produce CO2
    Therefore it occurs in both anaerobic and aerobic conditions.
  • Consumes two NAD+ and produces two NADH

In anaerobic conditions (in the erythrocyte, and in the setting of cellular hypoxia):

  • There is no oxygen available to allow further ATP production via the electron transport chain
    There is also no regeneration of NAD+ in the ETC.
  • In order for glycolysis to continue, NAD+ is regenerated via production of lactate

About 1400mmol of lactate is produced per day. Lactate is either:

  • Oxidised in the cell
    This requires restoration of NAD+, e.g. resolution of cellular hypoxia.
  • Circulated to the liver
    Lactate is then:
    • Oxidised to pyruvate
    • Converted to glucose
      This process is known as the Cori cycle.

Ketones

Ketones:

  • β-oxidation of fatty acids in the liver produces acetyl-CoA
  • Acetyl-CoA usually enters the citric acid cycle to produce ATP
  • When large amounts of acetyl CoA are produced, they may instead condense to form acetoacetate, which can then be reduced to β-hydroxybutyrate
    These substances are known as ketones

  • Ketones can only be produced by the liver, and only used as a substrate by the kidney, as well as skeletal and cardiac muscle

  • Production of ketones is accelerated by glucagon and adrenaline

References

  1. Kam P, Power I. Principles of Physiology for the Anaesthetist. 3rd Ed. Hodder Education. 2012.
  2. ANZCA August/September 2011
Last updated 2017-07-27

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