Kidney, Water, and Electrolytes

Abstract

INTRODUCTIONThe evolution of renal physiology has followed an interesting course in the past few years and has reflected the different approaches made possible by the development of new tools and methods of investigation. The improve ment and extension of the micropipetting techniques have brought the study of the control of electrolyte and water excretion from a consideration of balances of input and outgo for the whole kidney to knowledge of the fluxes and their control in segments of individual nephrons. Studies of slices, of homogenates, and of structural components of cells are dovetailing with the micropipetting experiments to provide data relating metabolic activities with electrolyte transport. Morphological studies of the electron microscopists are rapidly being extended to areas involving the renal circulation and its hor monal control. The investigation of the renal handling of a given substance requires consideration not only of renal structure and function but also of the circulation, of metabolic activities, and of the effects on the handling of other substances. The study of fragments of renal tissue is now directly comple mentary to the study of the intact organ in vivo. GLOMERULAR STRUCTURE AND FUNCTIONSome uncertainty remains concerning the initial step in the formation of urine. The applicability of the pore hypothesis to the passage of water and other substances across capillary walls and to the formation of glomerular fluid has been reviewed by Renkin (1). The calculated frequency of the 30-A pores is so small that their detection by electron micrography is considered unlikely. Winne (2) has presented modified derivations for the dilIusion hypothesis and for the pore filtration hypothesis and has proposed criteria for determining which of the processes is operative. In brief, comparison is made of the rate coefficients for transfer by the Fick diffusion equation for concen tration gradients of solute and of the rate coefficients for the thermodynamic and for the Hagen-PoiseuiUe-Pappenheimer equations for transfer of water. Values for the rate coefficients were calculated from older experimental data and the conclusion was reached that the transfers occurred through pores, albeit of a radius or-about 20 A rather than of 30 A. However, the rate coeffi-1 The survey of literature for this review was concluded in June 1963. No attempt has been made to review systematically material published in abstract form nor to provide complete coverage of all full articles.