Describe the production and metabolism of lactate.
Lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase
(LDH). Lactate is produced during normal metabolism and in increased quantities
during anaerobic metabolism. Candidates were expected to further describe this
A good answered required quantification of lactate production during normal aerobic
metabolism, during anaeorobic metabolism, the pathways involved (Glucose to
Pyruvate, Pyruvate to Citric Acid cycle in presence of Oxygen, Pyruvate + NADH to
Lactate + NAD+ without Oxygen) associated ATP production, site of intracellular
production, why red blood cells differ and lactate metabolism (eg oxidation to
pyruvate by well-oxygenated muscle cells which is then directly used to fuel the citric
acid cycle conversion to glucose via the Cori cycle in the liver through the process of
gluconeogenesis). Good answers illustrated the loss of energy potential with the
production of lactate and discussed the situations that would lead to an inbalance
between production and metabolism of lactate.
Candidates who did poorly in this question did so due to a lack of depth and breadth
for this topic. For example, even though the Cori Cycle was often mentioned, it was
poorly described in relation to lactate metabolism.
References: Textbook of Medical Physiology, Guyton Chp 67