Active Transport and Electrical Work
Jean-Louis Burgot in Thermodynamics in Bioenergetics, 2019
This chapter begins by considering a kind of transports through the biological membranes, that is to say the crossing across them under active transport and more precisely by considering what is named osmotic work. It gives some examples of such transports and conditions under which they are operating. The chapter also considers the case where an active transport results in a bioelectric phenomena such as an action potential . It briefly considers the notion of transcellular active transport . Contrary to the homocellular transport mechanism, transcellular active transport takes place across a whole cell or a whole layer of cells. In this process, the “pumps” work at different rates on the opposite sides of cells. “Pumps” may be of different kinds. When the nerve cell is excited by reception of an impulse from the next cell, or by electrical stimulation, it is found that a “wave” travels along the axon at a high rate.
Policy and Environmental Supports for Physical Activity and Active Living
James M. Rippe in Lifestyle Medicine, 2019
This chapter aims to identify for the lifestyle medicine practitioner evidence-based interventions that address policy and environmental supports for promoting physical activity that can reinforce a healthy lifestyle and active living assessment and counseling. Adults in developed countries report many barriers to participation in regular physical activity. Policy and environmental approaches for promoting physical activity are predicated on the basis of establishing a foundation on which the concept of a “physical activity friendly” community/space is created, whereby intersectoral efforts of physical activity programming, promotion, and civic action can yield greater success among community residents. School physical education and health education curricula provide methods of promoting youth physical activity, and many of the strategies have been shown to be effective. Active transport by walking and cycling to and from school can provide substantial physical activity for children and youth, as illustrated by a recent evaluation of the Safe Routes to School program.
Metabolism, nutrition, exercise and temperature regulation
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2015
Cells need energy for work including muscle contraction, biosynthesis, active transport across membranes and generation of heat. Energy is generated from metabolic fuels and from reduced molecules, which are oxidized to release energy. Oxidation involves removing electrons at high potential from the fuel molecules and transferring them to a lower potential, thus releasing energy. The removed electrons must be transferred to a suitable electron acceptor, which has to be transportable, soluble in water and generally available. Oxygen is not used until the end of the electron transport chain. The basic chemical currency of energy in all living cells consists of the two high-energy phosphate bonds contained in adenosine triphosphate (ATP). The immediate source of cellular energy is ATP, which can lose one phosphate group producing adenosine diphosphate and usable energy. The end product of glycolysis is pyruvate, which under aerobic conditions enters the citric acid cycle.
Human clearance prediction: shifting the paradigm
Published in Expert Opinion on Drug Metabolism & Toxicology, 2009
Thierry Lavé, Kathryn Chapman, Paul Goldsmith, Malcolm Rowland
There is a growing momentum to use in vitro methods, nestled in in silico physiologically based pharmacokinetic models as the primary source of prediction of human clearance. This represents a shift in the paradigm for predictions in humans, which has been traditionally based on in vivo empirical approaches involving allometric scaling. For hepatic clearance of lipophilic metabolised compounds, methodology for scaling based on in vitro data is well established and approaches based on in vitro data alone seem to be the most accurate. However, limitations in in vitro methods exist for compounds cleared by other mechanisms, such as those for which active transport is a major determinant of the hepatobiliary and renal elimination processes. A major challenge for any clearance prediction is the assessment of variability and uncertainty. Integrative and mechanistic approaches such as physiologically based scaling provide the most promising way of dealing with these aspects. In this review, the authors assess advances in in vitro methods for hepatic and renal clearance predictions with particular emphasis on mechanistic approaches.
Mathematical models of α-synuclein transport in axons
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2016
I.A. Kuznetsov, A.V. Kuznetsov
To investigate possible effects of diffusion on α-synuclein (α-syn) transport in axons, we developed two models of α-syn transport, one that assumes that α-syn is transported only by active transport, as part of multiprotein complexes, and a second that assumes an interplay between motor-driven and diffusion-driven α-syn transport. By comparing predictions of the two models, we were able to investigate how diffusion could influence axonal transport of α-syn. The predictions obtained could be useful for future experimental work aimed at elucidating the mechanisms of axonal transport of α-syn. We also attempted to simulate possible defects in α-syn transport early in Parkinson's disease (PD). We assumed that in healthy axons α-syn localizes in the axon terminal while in diseased axons α-syn does not localize in the terminal (this was simulated by postulating a zero α-syn flux into the terminal). We found that our model of a diseased axon predicts the build-up of α-syn close to the axon terminal. This build-up could cause α-syn accumulation in Lewy bodies and the subsequent axonal death pattern observed in PD (‘dying back’ of axons).
Direct and self-reported measures of physical activity and sedentary behaviours by weight status in school-aged children: results from ISCOLE-Kenya
Published in Annals of Human Biology, 2015
Stella K. Muthuri, Lucy-Joy M. Wachira, Vincent O. Onywera, Mark S. Tremblay
Background: Previous work has shown little association between self-report and directly measured physical activity. The objective of this study was to investigate the relationships between self-reported and directly assessed measures of physical activity and sedentary time by weight status in Kenyan children. Methods: Direct assessment of body weight, physical activity and sedentary time of 563 children was collected through anthropometry and accelerometry, while self-reported assessment was achieved by administering a questionnaire. Results: Under/healthy weight children had significantly higher directly measured mean daily minutes of moderate-to-vigorous physical activity (MVPA) compared to overweight/obese children (39 vs 20 minutes); had lower mean weekend-day minutes of sedentary time (346 vs 365 minutes); had a higher proportion who met accepted physical activity guidelines (15.3% vs 2.6%); and a higher number reported using active transportation to/from school (49.2% vs 32.4%). Self-reported time spent outside before and after school and active transport to/from school were significantly associated with mean weekday minutes of MVPA (r-value range = 0.12–0.36), but only for the under/healthy weight children. Conclusions: The results of this study found a number of differences in the accumulation of MVPA and sedentary time by weight status and weak-to-moderate correlations between self-report and direct measures of weekday and weekend-day physical activity among the under/healthy weight children.
Related Knowledge Centers
- Nephron
- Proximal Tubule
- Rna
- Metabolism
- Kidney
- Nuclear Membrane
- Biological Transport