Question 5

Describe the production and metabolism of lactate.

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College Answer

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 
physiological processes. 

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.
Syllabus: K2g
References: Textbook of Medical Physiology, Guyton Chp 67