Factors affecting proximal tubular reabsorption during development

1987 ◽  
Vol 252 (1) ◽  
pp. F188-F197 ◽  
Author(s):  
F. J. Kaskel ◽  
A. M. Kumar ◽  
E. A. Lockhart ◽  
A. Evan ◽  
A. Spitzer
Keyword(s):  
Proximal Tubule ◽  
Plasma Osmolality ◽  
Major Change ◽  
Postnatal Life ◽  
Urinary Recovery ◽  
Factors Affecting ◽  
Permeability Characteristics ◽  
Intercellular Channels ◽  
The Many ◽  
Glomerulotubular Balance

Studies performed in several animal species have demonstrated that glomerulotubular balance is maintained throughout development despite the many changes that occur in the factors known to control it. In an attempt to understand the nature of this phenomenon we quantified the magnitude and described the profile of these changes in guinea pigs. The changes in physical forces were assessed from measurements of hydrostatic and oncotic pressures, whereas those in the permeability characteristics of the proximal tubule epithelium were estimated from permeance to macromolecules of graded radii, histologic measurements of the intercellular channels, and measurements of end-proximal ratio of tubular fluid-to-plasma osmolality (TF/Posm). Between 1 and 50 days of age the net pressure for reabsorption increased from 15.0 to 30.9 mmHg (P less than 0.01, n = 15) with the major change occurring during the first 2-3 wk of postnatal life. The urinary recovery of inulin, sucrose, and creatinine, injected in the early segment of proximal tubules did not vary with age. The urinary recovery of mannitol (MW 180 daltons, Stokes-Einstein radius 4.0 X 10(-10) m) increased from 92% at birth to 100% at 49 days of age (P less than 0.001, n = 24), consistent with a decrease of approximately 0.5 X 10(-10) m in the luminal openings of the paracellular channels. The length of the zonulae occludens and the width of the intercellular channels did not change during this period; however, the length of the channels increased from 5.0 +/- 0.17 to 8.9 +/- 0.48 micron (P less than 0.01, n = 16). These changes should result in an increase in resistance across the intercellular channels. Consistent with this assertion is the observation that the mean TF/Posm of the fluid collected toward the end of the proximal convoluted tubule decreased as a function of age from 1.05 at day 2 to 0.98 at day 80 (P less than 0.001, n = 24). The findings support the hypothesis that during early postnatal life glomerulotubular balance is made possible by a high permeability of the proximal tubule, which compensates for the low net reabsorptive pressure. As the animal matures and the proximal tubule epithelium becomes tighter, for glomerulotubular balance to be maintained, an increase in the number of intercellular channels and in the active transport of sodium need to be postulated.

Pescadores migrantes: análisis de su dinámica e integración Social

2019 ◽  
Vol 37 (3) ◽  
pp. 18
Author(s):  
Fernando González Laxe
Keyword(s):  
Renewable Resources ◽  
Sustainable Management ◽  
Social Groups ◽  
Technological Innovations ◽  
Social Competition ◽  
Factors Affecting ◽  
Fish Stocks ◽  
Fishery Resources ◽  
Migration Dynamics ◽  
The Many

The globalization of the economy encourages massive population displacements and inevitably generates a cosmopolitization of societies. This leads to concern, misunderstanding and rejection. The most vulnerable social groups in society can perceive the population as intruders and enemies in social competition. Undoubtedly, the extreme spatial instability of fishery resources is among the many factors affecting migration dynamics. Various reasons for the mobility of fishermen are relevant around this concept. These include aspect related to traditions, to the capitalisation of activity, to technological innovations, and to innovation exchanges concerning the location of fish stocks. This article reflects on spatial increase of fishermen’s. The analyse are part of the paradigm of the sustainable management of common renewable resources, in particular fishery resources. It presents three lines of analysis: the reason for mobility; the choice of destination; and are the integration into host units.

Glomerulotubular balance in a mathematical model of the proximal nephron

1990 ◽  
Vol 258 (3) ◽  
pp. F612-F626 ◽  
Author(s):  
A. M. Weinstein
Keyword(s):  
Tight Junction ◽  
Proximal Tubule ◽  
Water Permeability ◽  
Water Flux ◽  
Salt Transport ◽  
Salt Flux ◽  
Filtration Fraction ◽  
Epithelial Junctions ◽  
Permeability Increase ◽  
Glomerulotubular Balance

A nonelectrolyte model of proximal tubule epithelium has been extended by the inclusion of a compliant tight junction. Here "compliance" signifies that both the junctional salt and water permeability increase and the salt reflection coefficient decreases in response to small pressure differences from lateral interspace to tubule lumen. In previous models of rat proximal tubule, there has been virtually no sensitivity of isotonic salt transport to changes in peritubular oncotic force. With the inclusion of junctional compliance, decreases in peritubular protein can open the junction and produce a secretory salt flux. Thus the model can represent the "backflux hypothesis," as it was originally put forth (J. E. Lewy and E. E. Windhager, Am. J. Physiol. 214: 943-954, 1968). Additional calculations, simulating a tight junction with negligible water permeability, reveal that the quantitative impact of peritubular protein can be realized whether or not there is substantial junctional water flux. The epithelial model of proximal tubule has also been incorporated into a model of the proximal nephron, complete with glomerulus, peritubular capillary, and interstitium. The interstitial compartment is well mixed and interstitial pressure and osmolality are determined iteratively to achieve balance between tubule reabsorption and capillary uptake. For this model, two domains of operation are identified. When interstitial pressures are low, junctions are closed, and filtration fraction has no effect on proximal reabsorption. When interstitial pressures are relatively elevated, epithelial junctions are open, and proximal salt reabsorption changes in proportion to changes in filtration fraction. In neither domain, however, does the model tubule augment salt flux with isolated increases in luminal flow rate (at constant filtration fraction). The absence of a separate effect of tubule fluid flow on salt transport precludes perfect glomerulotubular balance.

scholarly journals Proximal tubule apical endocytosis is modulated by fluid shear stress via an mTOR-dependent pathway

2017 ◽  
Vol 28 (19) ◽  
pp. 2508-2517 ◽  
Author(s):  
Kimberly R. Long ◽  
Katherine E. Shipman ◽  
Youssef Rbaibi ◽  
Elizabeth V. Menshikova ◽  
Vladimir B. Ritov ◽  
...  
Keyword(s):  
Shear Stress ◽  
Ion Transport ◽  
Proximal Tubule ◽  
Fluid Shear Stress ◽  
Kidney Development ◽  
Endocytic Pathway ◽  
Fluid Shear ◽  
Intermediate Phenotypes ◽  
Glomerulotubular Balance

Cells lining the proximal tubule (PT) have unique membrane specializations that are required to maintain the high-capacity ion transport and endocytic functions of this nephron segment. PT cells in vivo acutely regulate ion transport in response to changes in glomerular filtration rate (GFR) to maintain glomerulotubular balance. PT cells in culture up-regulate endocytic capacity in response to acute changes in fluid shear stress (FSS); however, it is not known whether GFR modulates PT endocytosis to enable maximally efficient uptake of filtered proteins in vivo. Here, we show that cells cultured under continuous FSS develop an expanded apical endocytic pathway and increased endocytic capacity and lysosomal biogenesis. Furthermore, endocytic capacity in fully differentiated cells is rapidly modulated by changes in FSS. PT cells exposed to continuous FSS also acquired an extensive brush border and basolateral membrane invaginations resembling those observed in vivo. Culture under suboptimal levels of FSS led to intermediate phenotypes, suggesting a threshold effect. Cells exposed to FSS expressed higher levels of key proteins necessary for PT function, including ion transporters, receptors, and membrane-trafficking machinery, and increased adenine nucleotide levels. Inhibition of the mechanistic target of rapamycin (mTOR) using rapamycin prevented the increase in cellular energy levels, lysosomal biogenesis, and endocytic uptake, suggesting that these represent a coordinated differentiation program. In contrast, rapamycin did not prevent the FSS-induced increase in Na+/K+-ATPase levels. Our data suggest that rapid tuning of the endocytic response by changes in FSS may contribute to glomerulotubular balance in vivo. Moreover, FSS provides an essential stimulus in the differentiation of PT cells via separate pathways that up-regulate endocytosis and ion transport capacity. Variations in FSS may also contribute to the maturation of PT cells during kidney development and during repair after kidney injury.

scholarly journals AN EXPERIMENTAL STUDY ON THE RELAXATION OF BOLTS

2015 ◽  
Vol 16 (1) ◽  
Author(s):  
Muhammad Abid ◽  
Muhammad Shahid Khalil ◽  
Hafiz Abdul Wajid
Keyword(s):  
Dynamic Behaviour ◽  
Relaxation Behaviour ◽  
Bolted Joint ◽  
Factors Affecting ◽  
Elastic Interactions ◽  
Short And Long Term ◽  
The Many ◽  
Almost All ◽  
Static Behaviour

Loss of pre-load with time, commonly known as ‘Relaxation’ is an established phenomena. Behaviour of a bolted joint depends upon the pre-load in the bolts in use, not the pre-load introduced by the mechanic. Loss of pre-load is expected due to the many factors such as embedment relaxation, gasket creep, elastic interactions, and vibration loosening or stress relaxation. In a gasketed joint, due to the gasket flexibility, relaxation is always substantial during preliminary passes, as 80 to 100% loss is not uncommon in almost all the bolts, resulting in a dynamic behaviour. Pre-load in a gasketed joint is stabilized and retained to certain extent in the final passes only. In a non-gasketed joint, due to no gasket and no rotation its static behaviour is concluded. This paper highlights the factors affecting the amount of relaxation with time and presents important considerations that can reduce this. Both the short and long term relaxations are recorded and a ‘best fit’ model for relaxation behaviour is derived.

scholarly journals Factors Affecting Palm Farmers’ Decisions to Dispense Plantage-Product Zakat in Labuhanbatu Selatan Regency

2018 ◽  
Vol 3 (3) ◽  
pp. 13-24
Author(s):  
Amalia Agustin Syn ◽  
Khalifah Muhammad Ali ◽  
Didin Hafidhuddin
Keyword(s):  
Logistic Regression ◽  
Regression Analysis ◽  
Logistic Regression Analysis ◽  
Fresh Fruit ◽  
Factors Affecting ◽  
Fresh Fruit Bunches ◽  
The Many

Zakat is one of the five points in rukun Islam and consists of two types: zakat nafs (soul) and zakat maal (wealth). One of the many kinds of zakat maal is plantage-product zakat. Labuhanbatu Selatan Regency is an area that contains 160,785.04 hectares of palm plantation land as recorded in 2016. The area also produced 7,493,696.18 tons of Fresh Fruit Bunches (FFB) in the same year. The objective of this study is to identify the potential of plantage-product zakat (specifically palm plantage) and analyze the factors that affect farmers’ decision to dispense plantage-product zakat in Labuhanbatu Selatan Regency. Logistic regression analysis was the method of analysis used in this study. Based on data obtained from Dinas Perkebunan Provinsi Sumatera Utara 2016, the potential of plantage-product zakat in Labuhanbatu Selatan Regency reached 25.6 billion rupiahs in 2014; 21.6 billion rupiahs in 2015, and 370.4 billion rupiahs in 2016. The variables that significantly affected farmers’ decisions to dispense plantage-product zakat were comprehension of zakat, faith, rewards, Islamic study, and frequency of worship.

scholarly journals ABOUT DEVELOPMENT FACTORS OF NATIONAL INNOVATIVE SYSTEMS

2020 ◽  
pp. 144-148
Author(s):  
А.П. Фомина ◽  
Р.А. Дрозд ◽  
М.И. Гайченя
Keyword(s):  
Innovation System ◽  
Innovation Process ◽  
National Innovation System ◽  
Innovative Development ◽  
Economic Policies ◽  
Factors Affecting ◽  
Innovation Infrastructure ◽  
The Many ◽  
Favorable Conditions ◽  
Push Model

Для достижения необходимого уровня конкурентоспособности экономики страны, развития национальной инновационной системы, требуется идентификация и актуализация факторов, оказывающих влияние на национальную инновационную систему, ее успешное функционирование. Из множества факторов, влияющих на инновационное развитие, необходимо выделить основные и второстепенные. В статье рассматриваются основные характеристики инновационного процесса, механизмы взаимодействия субъектов экономики и науки. Рассматриваются модели эндогенного роста и имитационного инновационного развития и интенсивного инновационного роста. При рассмотрении двух подходов к природе зарождения инновации: модель technology – push и модель market-pull, авторами выдвигается и подтверждается гипотеза о том, что фактором развития национальной инновационной системы является, прежде всего, реализация технологических инноваций. Авторами доказывается, что особое внимание необходимо уделить развитию научно-технической инновационной инфраструктуры. Развитие национальных инновационных систем может иметь секторальный характер: применение соответствующей экономической политики, стимулирующей развитие науки, технологий, инноваций в отдельных секторах экономики и кластерах, в которых под влиянием различных факторов сложились наиболее благоприятные условия для развития в сфере технологий. To achieve the required level of competitiveness of the country's economy, the development of a national innovation system, identification and updating of factors that influence the national innovation system and its successful functioning is required. Of the many factors affecting innovative development, it is necessary to distinguish the main and secondary. The article discusses the main characteristics of the innovation process, the mechanisms of interaction between economic entities and science. The models of endogenous growth and imitation innovative development and intensive innovative growth are considered. When considering two approaches to the nature of the origin of innovation: the technology-push model and the market-pull model, the authors put forward and confirm the hypothesis that the factor of development of the national innovation system is, first of all, the implementation of technological innovations. The authors prove that special attention should be paid to the development of scientific and technical innovation infrastructure. The development of national innovation systems can be of a sectoral nature: the application of appropriate economic policies that stimulate the development of science, technology, innovation in individual sectors of the economy and clusters, in which under the influence of various factors the most favorable conditions for development in the field of technology have developed.

Modeling for E-Learning Systems

2011 ◽  
pp. 2646-2650
Author(s):  
Maria Alexandra Rentroia-Bonito ◽  
Joaquim Armando Pires Jorge
Keyword(s):  
Organizational Context ◽  
Learning Curves ◽  
Future Trends ◽  
Factors Affecting ◽  
Social Barriers ◽  
Business Environments ◽  
E Learning ◽  
Expected Benefits ◽  
Based Instruction ◽  
The Many

Computer-based instruction is touted as an effective tool to support knowledge dissemination within predefined learning environments. Indeed, many see it as a way to overcome geographical or social barriers to knowledge transmission and educational institutions. However, its domain of application has traditionally been restricted to basic skills and educational contexts. Recently, dynamic and complex business environments shaped by technological changes and the downsizing trend of the ’90s placed new constraints on the underlying assumptions (Fuglseth, 2003). Organizations are now pushing for skill flexibility, demanding specialized knowledge and requiring faster learning curves from employees. Many advocate Internet-based education materials as one way to meet those challenges (Bernardes & O’Donoghue, 2003; Karoulis et al., 2004; Storey et al., 2002; Strazzo & Wentling, 2001). However, this raises important questions concerning both effectiveness and efficiency of such tools and materials. Indeed, developing interactive multimedia-based courseware remains pretty much a black art, consuming enormous resources. So far, there is a lack of established models to predict the performance and evaluate how adequately courseware can meet user needs. In fact, developing courseware should take into account the target constituency requirements, organizational context, and the stated educational or training goals. Developing the wrong training materials can lead to costly investments in creating and maintaining content to match the increasing expectations on e-learning. Perhaps this can explain the recent rash of failed e-learning projects—current results do not measure up to business and individual expectations yet. A better understanding of the many factors affecting e-learning performance would allow individuals and organizations to achieve the expected benefits. In so doing, development teams need methods, techniques, and tools to evaluate in advance which features are needed to achieve higher outcomes, namely, performance and satisfaction. Thus, the need to develop predictive models to improve learning effectiveness is in order. This overview includes four sections. “Background” presents a proposed e-learning theoretical framework to guide our analysis based upon the reviewed literature. “Key Issues” section describes main issues arising from the proposed elearning conceptual framework. “Future Trends” describes our vision on how to approach e-learning initiatives and future trends. Finally, we present a general conclusion.

A Reflective Essay of a Conceptual Model for Self-Directed Learning for the Adult Learner

2022 ◽  
pp. 163-172
Author(s):  
Maria Paradiso-Testa
Keyword(s):  
Seventh Century ◽  
Learning Theories ◽  
Traditional Learning ◽  
Self Directed Learning ◽  
Art And Science ◽  
Factors Affecting ◽  
Directed Learning ◽  
The Many ◽  
Emergent Theory ◽  
Reflective Essay

Of the many factors affecting our lives today, the ever-changing landscape of education is at the forefront. Learning is a complex behavior which involves cognitive, affective, and psychomotor domains. While pedagogy is the art and science of teaching children, andragogy is the art and science of teaching adults. The term pedagogy came into use in the seventh century. It wasn't until the 19th and 20th centuries that what we know as traditional learning theories—behaviorism, humanism, cognitivism, social cognitivism, and constructivism—were recognized. They were derived from the investigative tools of theorists—Pavlov, Skinner, Piaget, Freud, Maslow, Rogers, and Thorndike—to understand the nature of learning. In 1970, Malcolm Knowles promoted andragogy as a model of assumption that serves as a basis for an emergent theory. Today, the way of differentiating adult learners from children learners is through the process of andragogy.

Determinants of proximal tubular reabsorption as mechanisms of glomerulotubular balance

1978 ◽  
Vol 235 (2) ◽  
pp. F142-F150 ◽  
Author(s):  
B. J. Tucker ◽  
R. C. Blantz
Keyword(s):  
Proximal Tubule ◽  
Filtration Rate ◽  
Oncotic Pressure ◽  
Peritubular Capillary ◽  
Nephron Filtration Rate ◽  
Vein Occlusion ◽  
Proximal Tubular ◽  
Range Of Values ◽  
Proximal Tubular Reabsorption ◽  
Glomerulotubular Balance

The determinants of absolute proximal reabsorption (APR) were studied in four groups of rats during hydropenia, partial renal vein occlusion (RVO), saline expansion, and RVO after saline expansion. Nephron filtration rate (SNGFR), nephron plasma flow (RPF), APR, and proximal tubule (Pt) peritubular capillary (HPc), and interstitial (HPi) hydrostatic pressures were measured by micropuncture techniques. Subcapsular space (pii) and star peritubular capillary (piE) oncotic pressures were also determined. The peritubular capillary permeability coefficiency (LpAR) and the corresponding effective reabsorptive pressure (ERP) were computed, where APR = LpAR . ERP, and ERP = net reabsorptive pressure across the peritubular capillary. The results indicate that APR correlates best with SNGFR (P less than 0.05), but not with (pii - HPi), RPF, or LpAR. There was a significant relationship between piE and LpAR, where LpAR fell with increases in piE (P less than 0.01). In conclusion, 1) changes in absolute proximal reabsorption correlate best with changes in nephron filtration rate but not with (pii - HPi) across this range of values, 2) changes in efferent oncotic pressure (piiE) correlated inversely with LpAR, and 3) glomerulotubular balance in the proximal tubule can be partially attributed to intraluminal factors.

scholarly journals Renal NMDA receptors independently stimulate proximal reabsorption and glomerular filtration

2009 ◽  
Vol 296 (5) ◽  
pp. F976-F982 ◽  
Author(s):  
Aihua Deng ◽  
Scott C. Thomson
Keyword(s):  
Proximal Tubule ◽  
Glomerular Filtration ◽  
Functional Role ◽  
Filtration Rate ◽  
Channel Blocker ◽  
Tubuloglomerular Feedback ◽  
Minimal Impact ◽  
Nmda Channel ◽  
Single Nephron ◽  
Glomerulotubular Balance

N-methyl-d-aspartate receptors (NMDA) are expressed in the kidney, where little is known of their functional role. Several series of micropuncture experiments were performed in hydropenic rats using the NMDA channel blocker, MK801, and the NMDA coagonist, l-glycine, to probe NMDA for effects on single-nephron glomerular filtration rate (SNGFR) and proximal reabsorption ( Jprox). During intravenous infusion of MK801 or l-glycine, Henle's loop was perfused to manipulate SNGFR via tubuloglomerular feedback (TGF), thereby facilitating analysis of glomerulotubular balance. To confirm local actions on the kidney, MK801 was delivered to the glomerulus by microperfusion past the macula densa and to the proximal tubule by microperfusion into the early S1 segment. By all measures, MK801 acted on the glomerulus to reduce SNGFR, and acted on the proximal tubule to suppress Jprox, while having no effect on the responsiveness of TGF. l-Glycine raised SNGFR, dampened the TGF response, and could not be proved to independently stimulate proximal reabsorption. NMDA exerts a tonic vasodilatory influence on the glomerulus and a proreabsorptive effect on the proximal tubule. These combined effects allow NMDA to modulate SNGFR with minimal impact on late proximal flow. The full effects of l-glycine infusion on proximal tubule and TGF response do not extrapolate from the response to NMDA blockade.

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