Summary: The Two Most Common Kidney Stones

Because we synthesized the two most common kidney stones, calcium oxalate and calcium phosphate, we will focus on those two in the discussion of formation, treatment, and prevention. Calcium stones like calcium oxalate and calcium phosphate stones form when urine is “supersaturated with the constituent ions that comprise the stone” (Figge). This means, when urine is supersaturated with calcium and oxalate ion that type of stone is more likely to form. This supersaturation results from the ionic activity of Ca^(2+) and oxalate and Ca^(2+) and PO_4^(2-) is greater than the solubility of product for calcium oxalate and calcium phosphate (Figge). There can be various reasons for this supersaturation of ions. Concentrations of unbound calcium, oxalate and phosphate ions, urine pH, and other chemical presences can lead to calcium stones (Figge). Though kidney stone formation can be quite complicated, the formation of them is largely a solubility equilibrium problem where Le Chatelier’s Principle comes into play. Consider calcium oxalate stones that form from oxalic acid reacting with calcium ions.
CaC_2 〖O_4〗_((s) )⇌Ca_((aq))^(2+)+C_2 〖O_4^(2-)〗_((aq) )
This illustrates that the solubility product of calcium oxalate is solely dependent on the concentration of calcium ions and oxalic acid. If either component’s concentration is increased, the reaction shifts left leading to calcium oxalate formation. If we decrease the amount of oxalic acid or calcium ions, Le Chatelier’s Principle tells us that the reaction will shift to the right to create more Ca^(2+) and oxalic acid to maintain equilibrium and decrease the stress on the system (Uthayakumar). This same idea of shifting in equilibrium applies to calcium phosphate