Some aspects of flow and diffusion in the proximal tubule of the kidney

Copper oxide nanoparticles analysis with water as base fluid for peristaltic flow in permeable tube with heat transfer

The peristaltic flow of a copper oxide water fluid investigates the effects of heat generation and magnetic field in permeable tube is studied. The mathematical formulation is presented, the resulting equations are solved exactly. The obtained expressions for pressure gradient, pressure rise, temperature, velocity profile are described through graphs for various pertinent parameters. It is found that pressure gradient is reduce with enhancement of particle concentration and velocity profile is upturn, beside it is observed that temperature increases as more volume fraction of copper oxide. The streamlines are drawn for some physical quantities to discuss the trapping phenomenon.

Effects of chronic hyperfiltration on proximal tubule bicarbonate transport and cell electrolytes

The compensatory response to unilateral nephrectomy (UNX) was investigated by a combination of renal clearance, microperfusion, electron microprobe, and morphological techniques. Filtration rate was significantly elevated 21 days following UNX and associated with a marked stimulation of bicarbonate and fluid absorption in the proximal tubule. Analysis of kinetic data of bicarbonate transport demonstrated strong flow-dependent activation of bicarbonate absorption in both control and experimental condition. The bicarbonate level at which half-saturation (apparent Kd) of transport occurred decreased uniformly at higher flow rates, but maximal transport rates (apparent Vmax) in the proximal tubule doubled in the remnant kidney. The flow dependence of bicarbonate transport in control and experimental conditions can be explained by an apparent unstirred layer effect modifying radial bicarbonate gradients in the tubule. Both Na/H-exchange and electrogenic H secretion contribute to bicarbonate absorption, but only Na/H-exchange increased significantly in proximal tubules of UNX rats. Cell ion concentrations after UNX were unchanged in cortical tubules, consistent with proportionately enhanced apical and basolateral ion transport. Proximal tubule cell rubidium concentration measured after a 30-second rubidium infusion as an index of basolateral Na,K-ATPase activity was unchanged in UNX rats. Inasmuch as cell volume increased significantly (25%), these data are consistent with a proportionate and similar stimulation of rubidium uptake and Na,K-ATPase activity.

Performance of one- and two-dimensional models for a slow flow system in a long, permeable tubule

A radially symmetric slow flow system in a long cylinder with moderate wall leakage is considered, with physical parameters taken from the renal proximal tubule. Dimensional analysis yields a simplified system which, under certain assumptions, is well-posed, and possesses a unique solution if a solution exists. A lumped parameter analysis generates a one-dimensional model identical to a typical one-dimensional model in a special case. The one- and two-dimensional models agree well in the situations examined. When the wall fluxes are of a certain class, the concentration to which the solution tends as the fluid proceeds down the tubule can be computed algebraically.

A functional model of the rat kidney

A mathematical model of the nephron was developed by writing a set of material balance equations for the flow of urea, salt and water along the foregoing study and are taken here as a basis, in particular the model configuration of the collecting duct system. The stimulation of the model equatentration profiles which at the ends of the several tubular sections were consistent with the values observed in experimental investigations.e medullary interstitial solute concentration profiles are taken to increase linearly in outer and inner zone. The several transeptithelial fluxes are driven by diffusion, osmosis, solvent drag and active transport. The development of osmotic gradient in the inner medulla is taken here to be caused by active secretion of salt into the descending LImb of Henle's loop. The parameters in the flux equations for all parts of the nephron and the concentration values at the end of each tubular section are determined by collecting and averaging the values given in literature and by extrapolating the measurement data. The simulation of the model equations with these averaged parameters resulted in concentration profiles which at the ends of the several tubular sections were consistent with the values observed in experimental investigations.

Examination of transport equations pertaining to permeable elastic tubules such as Henle's loop

The transport equations applicable to loops of Henle and similar elastic permeable tubules were re-examined to assess the effect of radial transport resistance in the lumen and tubule geometry on solute transport. Active transport at the wall as well as external gradients equivalent to a 2--1,000-fold concentration increase per centimeter of distance were considered. Wall permeabilities and active transport constants were varied up to 2 . 10(-2) cm/s. It is shown that for conditions applicable to the loop of Henle, resistance to radial solute transfer in the lumen is negligible, both for passive and active transmural transport with concomitant water flux, and that axial dispersion further reduces that resistance. These conclusions apply equally to conical and elliptical geometries likely to arise in loop operation. The validity of Poiseuille's equation for these geometries is discussed. Ii is concluded that the one-dimensional transport equations are a valid representation of loop operation.

Mechanism of glomerulotubular balance. I. Effect of aortic constriction and elevated ureteropelvic pressure on glomerular filtration rate, fractional reabsorption, transit time, and tubular size in the proximal tubule of the rat

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