Articulo renal

Kidney International, Vol. 2 (1972), p. 85—94

Concentration

of urine in a central core model of the renal counterfiow system
JOHN L. STEPHENSON

National Heart and Lung Institute and Mathematical Research Branch, National Institute of Arthritis and Metabolic diseases, National Institutes of Health, Bethesda, Maryland

Concentration of urine in a central core model of the renalcounterflow system. In this model descending Henle's limbs
(DHL), ascending Henle's limbs (AHL) and collecting ducts (CD) exchange with a central vascular core (VC) formed by vasa recta loops—assumed so bighly permeable that the core functions as a single tube, open at the cortical end and closed at the papillary end. Solute supplied to the VC primarily by AHL increases VC

de Na+ dans la médullaireexterne et le cortex a la concentration dans Ia médullaire interne.

osmolality and so extracts water from Dh and CD, increasing their osmolality while diluting AHL fluid. This single effect multiplied by the counterflow arrangement leads to a high papillary osmolality in all structures. Some of the solute may
enter DHL to be recycled. In single solute system energy require-

Since the originalproposal by Kuhn and Ryffel [1], it has gradually become accepted that in some way the mammalian kidney utilizes the renal counterfiow system to concentrate urine. Experimentally it is firmly established that osmolality

in blood vessels, nephrons and interstitium increases from

ments for transport out of AHL decrease from outer to inner
medulla. In two solute systems (e.g. salt and urea)mixing in the central core can supply part of the energy for the final concentration of urine. Urea cycling, regulated by ADH, allows active Na+

cortex to papilla [2—4]. Micropuncture data from late proximal and early distal tubules indicate that solute in excess of its isotonic complement of water is removed from the loop of Henle [5, 6]. Micropuncture data from
the papilla show that soluteconcentration in the ascending limb (AHL) is less than in the descending limb (DHL) at

transport in the outer medulla and cortex to be used for concentration in the inner medulla.

the same papillary level [7] and that there is net solute
removal from the AHL [8]. These data are consistent with the hypothesis that the single effect for medullary concentration is solute transport out of theAHL. Split drop experiments [9] and experiments on perfused tubules [10], however, have given no evidence of Na + transport against a gradient out of the thin segment of AHL, and microscopically the epithelium of the thin AHL is atypical of epithelia

Concentration de l'urine dans un modèle a noyau central du

système a contre courant renal. Dans ce modéle Ia branche
descendante de l'anse deHanlé (DHL), Ia branche ascendante de l'anse de Henlé (AHL) et les canaux collecteurs (CD) échangent avec un noyau central vasculaire (VC) formé par les anses des vasa recta que l'on suppose si hautement perméables que le noyau fonctionne comme un tube unique ouvert a l'extrémité corticale et fermé a l'extrémité papillaire. Les substances dis-

soutes initialement délivrées au VC par AHL augmententl'osmolalité du VC et, par consequent, extraient de l'eau de
DHL et CD, augmentant l'osmolalité de ces derniers cependant que le liquide en AHL est dilué. Cet effet Clémentaire, multiplié

which vigorously transport Na+. Further complications
are that salt and urea, as well as water, leave the collecting

par Ia disposition a contre-courant, aboutit a une osmolalité
papillaire élevée danstoutes les structures. Une partie des substances dissoutes peut pénétrer dans DHL pour étre recyclée.

ducts (CD), and the parallel counterflow system of the ascending vasa recta (AVR) and descending vasa recta
(DVR) interacts with that of the nephrons. Previous theoretical models of the medullary counterflow system [11—20] have omitted some essential feature of the

Dans les systémes a une...