Countercurrent multiplication system without active transport

Rolando Claure-Del Granado
Hospital Obrero #2 – CNS, Universidad Mayor de San Simón

Total body water content is largely determined by the total amount of salt in the body, and the kidneys ultimately control the salt and water concentration. Despite wide fluctuations in the intake of salt and water, the renal mechanisms maintain the serum sodium chloride concentration within a very narrow range. The kidneys can perform this critically important regulatory role by virtue of being the target organ of various stimuli regulating salt and water homeostasis. Our understanding of the mechanisms by which the kidney can generate both dilute and concentrated urine was made possible by a description of how the operation of the countercurrent multiplication system works.

Wirtz et al. initially developed the general architecture of the renal countercurrent multiplication system in 1951(1). Since that initial description, several alternate models of countercurrent multiplication systems were proposed; however, most of these models were advanced by theoretic arguments without experimental basis.

In 1972, Kokko and Rector (2) proposed a completely new model of the countercurrent multiplication system. The fundamental difference between this and previous models was that the new model removed the necessity of postulating active transport processes in the thin ascending limb. This model was therefore consistent with experimental results and satisfied the mathematical formulations simultaneously developed by Stephenson(3). The model developed by Kokko and Rector stressed the importance of urea recirculation and allowed for an understanding of the pathophysiology behind many of the clinical states associated with a deranged balance of sodium and water.

References

  1. Kokko JP. The role of the renal concentrating mechanisms in the regulation of serum sodium concentration. Am J Med. 1977;62(2):165-9.
  2. Kokko JP, Rector FC, Jr. Countercurrent multiplication system without active transport in inner medulla. Kidney Int. 1972;2(4):214-23.
  3. Stephenson JL. Concentration of urine in a central core model of the renal counterflow system. Kidney Int. 1972;2(2):85-94.

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