Derivation of an Expression for the Rate of Formation of Glomerular Fluid (GFR). Applicability of Certain Physical and Physico-Chemical Concepts

Abstract

A derivation is presented, based on thermodynamic considerations and the concept of chemical potentials, for the rate of formation of glomerular fluid (GFR). The limitations of the derived formulations are discussed. The 2 mechanisms, filtration in bulk and diffusion, suggested for the passage of substances across capillary walls are defined. It is shown that the hypothesis of bulk flow through pores is not compatible with the exptly. detd. conditions for no net movement of water and that the concept of diffusion across capillary walls is valid as a working hypothesis. Tentative calculations based on the diffusion hypothesis and the thermodynamic formulation, have been made of the surface areas involved in the passage of water across the glomerular capillaries and across the peritubular capillaries. The result are of the same order of magnitude as those obtained by other methods of calculation. The results suggest that the whole capillary surface area is involved in the passage of water rather than just the intercellular cement substance.