In normal function of this cycle for respiration, concentrations of TCA intermediates remain constant; however, many biosynthetic reactions also use these molecules as a substrate.
Anaplerosis is the act of replenishing TCA cycle intermediates that have been extracted for biosynthesis (in what are called anaplerotic reactions).
[1] There are five major reactions classed as anaplerotic, and it is estimated that the production of oxaloacetate from pyruvate has the most physiologic importance.
[3] Anaplerotic enzymes mediate an alternative pathway to insulin secretion by aiding the production of cytosolic signal molecules.
[4] Pancreatic β-cells, which regulate blood glucose level by secreting insulin, contain high a mounts of pyruvate carboxylase.