Inner medullary external osmotic driving force in a 3-D model of the renal concentrating mechanism

1995 ◽  
Vol 269 (2) ◽  
pp. F159-F171 ◽  
Author(s):  
S. R. Thomas ◽  
A. S. Wexler
Keyword(s):  
Driving Force ◽  
Three Dimensional ◽  
Renal Medulla ◽  
Three Dimensional Model ◽  
A Value ◽  
Math Biol ◽  
Collecting Ducts ◽  
The Face ◽  
Renal Concentrating Mechanism ◽  
External Driving

The mechanism by which the renal medulla establishes and maintains a gradient of osmolarity along the corticomedullary axis, especially in the inner medulla, where there is no active transmural flux out of the ascending limbs of Henle, remains a source of controversy. We show here that, if realistic values of urea permeability in the inner medullary descending limbs and water permeability in the upper inner medullary section of the collecting ducts are taken into account, even a model including the three-dimensional vascular bundle structures [A. S. Wexler, R. E. Kalaba, and D. J. Marsh. Am. J. Physiol. 260 (Renal Fluid Electrolyte Physiol. 29): F368-F383, 1991] fails to explain the experimentally observed inner medullary osmolality gradient. We show here that this failure can be overcome by application of an external osmotic driving force, an idea recently revived by J. F. Jen and J. L. Stephenson (Bull. Math. Biol. 56: 491-514, 1994) in the context of a single-solute, single-loop central core model. We show that inclusion of such an external driving force with a value equivalent to at least 100 mosM of inner medullary interstitial osmolytes in the three-dimensional model of Wexler et al. accounts for a physiological osmolality gradient, even in the face of realistic permeability values. Furthermore, inclusion of the external driving force makes the model less dependent on the positions of descending and ascending limbs of Henle with respect to the collecting ducts. In an effort to assess whether there is any experimental basis for osmolytes, we show that a significant amount of extra inner medullary interstitial osmolytes is plausible, based on extrapolation from existing experimental data.

The effects of collecting duct active NaCl reabsorption and inner medulla anatomy on renal concentrating mechanism

1996 ◽  
Vol 270 (5) ◽  
pp. F900-F911 ◽  
Author(s):  
X. Wang ◽  
A. S. Wexler
Keyword(s):  
Collecting Duct ◽  
Three Dimensional ◽  
Hydraulic Permeability ◽  
Three Dimensional Model ◽  
Duct Epithelium ◽  
Collecting Ducts ◽  
Renal Concentrating Mechanism ◽  
Medullary Collecting Duct ◽  
Collecting Duct Epithelium

First, the representation of the inner medulla incorporates an exaggerated radial separation between tubules, vessels, and collecting ducts; and, second, the hydraulic permeability in the upper portion of the inner medullary collecting ducts was erroneously set to zero. In the current work, we explore the role of collecting duct hydraulic permeability and anatomical heterogeneity via mathematical modeling. The model predicts concentrated urine for measured values of the hydraulic permeability and homogeneous lower inner medulla as long as net active NaCl reabsorption is incorporated in the upper inner medullary collecting duct epithelium. This new three-dimensional model results in two recycling paths. The upper portion of the inner medulla recycles NaCl, whereas the lower portion recycles urea.

Three-dimensional anatomy and renal concentrating mechanism. I. Modeling results

1991 ◽  
Vol 260 (3) ◽  
pp. F368-F383 ◽  
Author(s):  
A. S. Wexler ◽  
R. E. Kalaba ◽  
D. J. Marsh
Keyword(s):  
Fluid Transport ◽  
Three Dimensional ◽  
Renal Medulla ◽  
Local Concentration ◽  
Concentration Gradients ◽  
Cylindrically Symmetric ◽  
Vasa Recta ◽  
Collecting Ducts ◽  
Renal Concentrating Mechanism ◽  
Distal Tubules

Simulations were performed to test the hypothesis that the three-dimensional organization of the renal medulla is essential for formation of hypertonic urine. As in previous models, representations of loops of Henle, distal tubules, collecting ducts, and vasa recta and recent estimates of tubule characteristics were included in a simulation of NaCl, urea, and fluid transport. In addition, this model specifies the relative positions of the medullary structures. By assuming that the structure of the minimum functional unit is a vascular bundle surrounded by tubules and ascending vessels, we have represented the three-dimensional organization of the medulla by a cylindrically symmetric two-dimensional model. The resulting set of equations gives rise to a nonlinear boundary value problem with linear boundary conditions, which was solved numerically via quasi linearization. Compared with previous simulations, the concentrations predicted by this model more accurately match measured quantities in two regards. First, papillary tip concentrations of NaCl and urea are significantly higher, and, second, a monotonic increase in osmolarity is observed in the inner medulla. The three-dimensional organization permitted development of local concentration gradients, which are essential to the final result.

Experimental tests of three-dimensional model of urinary concentrating mechanism.

1992 ◽  
Vol 2 (12) ◽  
pp. 1677-1688
Author(s):  
J S Han ◽  
K A Thompson ◽  
C L Chou ◽  
M A Knepper
Keyword(s):  
Water Permeability ◽  
Collecting Duct ◽  
Three Dimensional ◽  
Renal Medulla ◽  
Osmotic Gradient ◽  
Osmotic Water Permeability ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Osmotic Water ◽  
Collecting Ducts

Recently, a new model of the urinary concentrating process has been proposed that takes into account the three-dimensional architecture of the renal medulla. Under the assumptions of the model, computer simulations predicted significant axial osmolality gradients in the inner medulla without active transport by the inner medullary loop of Henle. Two of the model assumptions (which constitute hypotheses for this study) were: (1) the osmotic water permeability of the initial part of the inner medullary collecting duct (initial IMCD) is very low even in the presence of vasopressin; and (2) there is significant lateral separation of structures such that thin descending limbs are far from the collecting ducts at the same inner medullary level. The first hypothesis was addressed by perfusing rat initial IMCD segments in vitro and measuring osmotic water permeability. With the osmotic gradient oriented as predicted by the model (lumen greater than bath), vasopressin increased the osmotic water permeability from 286 to 852 microns/s. Three additional series of experiments confirmed the high water permeability in the presence of vasopressin. The second hypothesis was addressed by morphometric analysis of histologic cross-sections of the rat renal medulla. Mean distances of descending limbs to the nearest adjacent collecting duct were very small throughout the inner medulla (less than 6 microns) and substantially less than in the outer medulla (28 microns). It was concluded that the data are inconsistent with both hypotheses and therefore do not support the feasibility of the "three-dimensional" model of the renal inner medulla. The axial distributions of loops of Henle and collecting ducts in the rat renal medulla are also reported.

Use of computed tomography data for forensic identification of an individual

2020 ◽  
Vol 6 (4) ◽  
pp. 41-45
Author(s):  
Sergey V. Leonov ◽  
Julia P. Shakiryanova
Keyword(s):  
Computed Tomography ◽  
Computer Tomography ◽  
Soft Tissues ◽  
Three Dimensional ◽  
Reference Points ◽  
Forensic Identification ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
The Face ◽  
Tomography Data

Background: The article presents our own experience of using computer tomography for identification of individuals with known results. Aims: The aim of the study was to verify the possibility of performing an identification study using a three-dimensional model obtained from computed tomography of the head. Identification was performed using a three-dimensional model of the head, based on computer tomography sections made in various projections, with a step of 1.231.25 mm. Two-dimensional images of the face (photos) were used for comparison. All comparative studies were conducted using approved methods of craniofacial and portrait identification: by reference points and contours. The experiment used a computer program that allows you to export DICOM-files of computed tomography results to other formats (InVesalius), as well as computer programs that directly work with the research objects (Autodesk 3ds Max, alternative programs Adobe Photoshop, Smith Micro Poser Pro). Results: In the course of research, it was found that, having computer tomography data of the head, it is possible to conduct identification studies on the following parameters: on the reconstructed three-dimensional model of the soft tissues of the face, on the three-dimensional model of the skull (craniofacial identification), on the features of the structure of the ear. Conclusion: Positive results were obtained when comparing objects, which makes it advisable to use them in practical and scientific activities.

J-Estimation Schemes for Internal Circumferential and Axial Surface Cracks in Pipe Elbows

1998 ◽  
Vol 120 (4) ◽  
pp. 418-423 ◽  
Author(s):  
R. Mohan ◽  
A. Krishna ◽  
F. W. Brust ◽  
G. M. Wilkowski
Keyword(s):  
Shell Model ◽  
Driving Force ◽  
Three Dimensional ◽  
Surface Cracks ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Crack Driving Force ◽  
Cracked Structures ◽  
Axial Surface ◽  
J Estimation

In the spirit of GE/EPRI fracture mechanics procedure, estimation schemes for the crack driving force for circumferentially and axially surface-cracked pressurized elbows subjected to bending are developed. These schemes are based on the results of line-spring/shell model. The line-spring/shell model offers an attractive and inexpensive alternative to performing a large number of analyses of surface-cracked structures. This model has been shown to provide accurate predictions in comparison with the more involved three-dimensional model by Mohan (1998). Using the results of this model and following the GE/EPRI procedure, the coefficient functions, F1 and h1, which provide the necessary information for predicting the crack driving force in cracked elbows, for several elbow and crack geometries are tabulated.

Automatic derivative evaluation in solving boundary value problems: the renal medulla

1986 ◽  
Vol 251 (2) ◽  
pp. F358-F378 ◽  
Author(s):  
A. S. Wexler ◽  
R. E. Kalaba ◽  
D. J. Marsh
Keyword(s):  
Boundary Value ◽  
Three Dimensional ◽  
Renal Medulla ◽  
Dimensional Structure ◽  
Multiple Shooting ◽  
Automatic Evaluation ◽  
Systems Of Equations ◽  
Shooting Methods ◽  
Renal Concentrating Mechanism ◽  
Large Systems

Automatic evaluation of derivatives becomes essential when large systems of equations of many variables are to be solved. This paper presents a set of easy-to-use FORTRAN subroutines that perform automatic derivative evaluation. They were used in conjunction with the method of quasilinearization to solve a 13th-order boundary-value problem. This problem has been proposed as a test of numerical methods used to solve models of the renal concentrating mechanism. Quasilinearization gives the same result as has been reported by others with finite difference or multiple shooting methods. The approach described here offers the important potential advantage of being easier to apply to larger problems, which can be anticipated when attempts are made to simulate the three-dimensional structure of the renal medulla.

Reevaluating Constructivist Norm Theory: A Three-Dimensional Norms Research Program

2022 ◽  
Vol 24 (1) ◽  
Author(s):  
Jeffrey S Lantis ◽  
Carmen Wunderlich
Keyword(s):  
Three Dimensional ◽  
World Politics ◽  
Three Dimensions ◽  
Research Progress ◽  
Three Dimensional Model ◽  
Critical Dimensions ◽  
Complex Processes ◽  
Syrian Civil War ◽  
Spatial Dimensions ◽  
The Face

Abstract Constructivist theories of norm dynamics offer a variety of analytical tools to understand the complex processes of norm emergence, diffusion, and evolution over time. As the literature has developed, though, it lacks a general framing of the interconnections between norms, norm clusters or configurations, and principles or “normativity.” This article advances a new three-dimensional model of constructivist theories of norms that emphasizes the spatial dimensions of norm meanings, legitimacy, and impact and identifies promising avenues for research progress. First, individual norms represent a primary intersubjective structural component that is both developed and contested. Second, theories of norm interrelations or norm clusters provide additional critical dimensions of structuration that may promote resiliency in the face of contestation. Third, norms exist within a larger constellation of norm structures, representing the broadest dimension in world politics. Collisions can occur in this environment, but broader normativity and institutionalization often become activated in the face of serious challenges. As demonstrated using the illustration of international responses to the Syrian civil war (2011 till present), only by attending to all three dimensions of norms can we gain a more accurate understanding of real-world circumstances of norm connections, norm collisions, and the variable effects of norm contestation. The article concludes by identifying promising research avenues building from the three-dimensional framework.

CAN THE DICE BE FAIR BY DYNAMICS?

2010 ◽  
Vol 20 (04) ◽  
pp. 1175-1184 ◽  
Author(s):  
J. STRZALKO ◽  
J. GRABSKI ◽  
A. STEFANSKI ◽  
T. KAPITANIAK
Keyword(s):  
Three Dimensional ◽  
Initial Energy ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
The Face

We consider the dynamics of the three-dimensional model of the die which can bounce with dissipation on the table. It is shown that for the realistic values of the initial energy the probabilities of the die landing on the face which is the lowest one at the beginning is larger than the probabilities of landing on any other face.

scholarly journals Electrostatic interaction between Interball-2 and the ambient plasma. 1. Determination of the spacecraft potential from current calculations

2002 ◽  
Vol 20 (3) ◽  
pp. 365-376 ◽  
Author(s):  
M. Bouhram ◽  
N. Dubouloz ◽  
M. Hamelin ◽  
S. A. Grigoriev ◽  
M. Malingre ◽  
...  
Keyword(s):  
Complex Geometry ◽  
Three Dimensional ◽  
Field Measurements ◽  
Three Dimensional Model ◽  
Charge Densities ◽  
A Value ◽  
Spacecraft Potential ◽  
Potential Structure ◽  
Particle Simulations

Abstract. The Interball-2 spacecraft travels at altitudes extending up to 20 000 km, and becomes positively charged due to the low-plasma densities encountered and the photoemission on its sunlit surface. Therefore, a knowledge of the spacecraft potential Fs is required for correcting accurately thermal ion measurements on Interball-2. The determination of Fs  is based on the balance of currents between escaping photoelectrons and incoming plasma electrons. A three-dimensional model of the potential structure surrounding Interball-2, including a realistic geometry and neglecting the space-charge densities, is used to find, through particle simulations, current-voltage relations of impacting plasma electrons Ie (Fs ) and escaping photoelectrons Iph (Fs ). The inferred relations are compared to analytic relationships in order to quantify the effects of the spacecraft geometry, the ambient magnetic field B0 and the electron temperature Te . We found that the complex geometry has a weak effect on the inferred currents, while the presence of B0 tends to decrease their values. Providing that the photoemission saturation current density Jph0 is known, a relation between Fs and the plasma density Ne can be derived by using the current balance. Since Jph0 is critical to this process, simultaneous measurements of Ne from Z-mode observations in the plasmapause, and data on the potential difference Fs  - Fp  between the spacecraft and an electric probe (p) are used in order to reverse the process. A value Jph0 ~ = 32 µAm-2 is estimated, close to laboratory tests, but less than typical measurements in space. Using this value, Ne and Fs  can be derived systematically from electric field measurements without any additional calculation. These values are needed for correcting the distributions of low-energy ions measured by the Hyperboloid experiment on Interball-2. The effects of the potential structure on ion trajectories reaching Hyperboloid are discussed quantitatively in a companion paper.Key words. Space plasma physics (charged particle motion and acceleration; numerical simulation studies; spacecraft sheaths, wakes, charging)

Cycles and separations in a model of the renal medulla

1998 ◽  
Vol 275 (5) ◽  
pp. F671-F690 ◽  
Author(s):  
S. Randall Thomas
Keyword(s):  
Three Dimensional ◽  
Renal Medulla ◽  
Distal Tubule ◽  
Progressive Increase ◽  
Transport Parameter ◽  
Three Dimensional Model ◽  
Modeling Analysis ◽  
Vasa Recta ◽  
Adjusted Model

This study gives the first quantitative analysis of net steady-state transmural fluxes of water, urea, and NaCl in a numerical model of the rat renal medulla in antidiuresis, revealing the model’s predictions of water, urea, and NaCl cycling patterns. These predictions are compared both to in vivo micropuncture data from the literature and to earlier qualitative proposals (e.g., K. V. Lemley and W. Kriz. Kidney Int. 31: 538–548, 1987) of cycling and exchange patterns based on medullary anatomy and available permeability and transport parameter measurements. The analysis is based on our most recent three-dimensional model [X. Wang, S. R. Thomas, and A. S. Wexler. Am. J. Physiol. 274 ( Renal Physiol. 43): F413–F424, 1998]. In general agreement with earlier proposed patterns, this analysis predicts the following: 1) important water short-circuiting from descending structures to ascending vasa recta in most medullary regions, 2) massive urea recycling in the upper inner medulla, 3) a progressive increase of the ratio of urea to total osmoles along the corticopapillary axis, 4) urea dumped from the collecting ducts (CD) into the deep papilla is returned to the cortex essentially via outer medullary short vasa recta, bearing witness to a shift from the long descending limbs and vasa recta of the inner medulla (IM) to short structures in the outer medulla (OM). The analysis also shows that the known radial heterogeneity of the inner stripe (IS) implies unequal osmolalities in long descending limbs, vasa recta, and CDs entering the IM across the OM/IM border and explains the model’s unorthodox osmolality profile along the CD. In conflict with micropuncture evidence of a doubling of urea flow in superficial Henle’s loops (SHL) between the end proximal and early distal tubule (T. Armsen and H. W. Reinhardt. Pflügers Arch. 326: 270–280, 1971), the model predicts net urea loss from SHL due to the model’s inclusion of nonneglible measured urea permeability of medullary thick ascending limbs [M. A. Knepper, Am. J. Physiol. 245 ( Renal Fluid Electrolyte Physiol. 14): F634–F639, 1983]. We present a suite of adjusted model permeabilities that improves agreement with the micropuncture data on this point. In conclusion, this modeling analysis of solute and water recycling serves as a quantitative check on qualitative propositions in the literature and allows closer critical comparison of model behavior with published experimental results than was heretofore possible.

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