title: Concentration profiles of calcium and oxalate in urine, tubular fluid and renal tissue--some theoretical considerations.
abstract: This paper analyzes some aspects of the pathophysiology of urolithiasis. It is emphasized that a better understanding of factors contributing to stone formation can only be gained when the primary nucleation site is identified. Three compartments are considered in which supersaturation as a precondition for stone formation could be present: urine in the urinary tract, tubular fluid from the glomerulus down to the duct of Bellini, and the interstitium of the medulla. From calculations based on micropuncture data it becomes apparent that the oxalate concentration in the tubular fluid at the bend of Henle's loop is 1 or 2 orders of magnitude lower than in the duct of Bellini and that the oxalate concentration maximum invariably must be located in the final urine. The calculation of a tubular concentration profile of oxalate shows, that the probability of intra luminal crystal formation is even less likely for plasma oxalate values of 2-3 microM as compared to 1.2 microM, which therefore should be the correct value. The time necessary for the growth of crystals up to a critical size which can obstruct tubules or ureter is not available in the urinary tract nor in the tubules. However, in the medullary interstitium, where solute concentration is highest, nearly unlimited time for crystal growth is available due to the fact, that in this compartment convective flow is very low. It is concluded that the interstitium of the inner medulla has the best chances to function as the primary nucleation site where particles can be formed of a size which subsequently can obstruct the urinary tract.
mesh_terms: D002118:Calcium / Q000378:metabolism* / Q000652:urine; D003460:Crystallization; D005919:Glomerular Filtration Rate; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D007679:Kidney Medulla / Q000378:metabolism; D007684:Kidney Tubules / Q000378:metabolism; D009399:Nephrons / Q000378:metabolism; D010070:Oxalates / Q000378:metabolism* / Q000652:urine; D019815:Oxalic Acid; D014545:Urinary Calculi / Q000378:metabolism* / Q000652:urine; D014563:Urodynamics
chemical_list: D010070:Oxalates; D019815:Oxalic Acid; D002118:Calcium