Transport mechanisms overview

The following sections provide an overview of the application of the IPL for the study of drug absorption. Examples are provided to illustrate the use of the IPL to study drug permeability, absorption profiles, transport mechanisms and the effects of inhaled dose formulation on drug disposition. 

Fig. 1. Overview of intravascular heme catabolism. Hemoglobin, myoglobin, and other heme proteins are released into the circulation upon cellular destruction, and the heme moiety is oxidized by O2 to the ferric form (e.g., methemoglobin and metmyoglobin). Haptoglobin can bind a substantial amount of hemoglobin, but is readily depleted. Ferric heme dissociates from globin and can be bound by albumin or more avidly by hemopexin. Hemopexin removes heme from the circulation by a receptor-mediated transport mechanism, and once inside the ceU heme is transported to heme oxygenase for catabolism.

For the oscillations we have discussed so far, the only requirement on the interfacial kinetics of the system is that it possess an N-NDR. Oscillations come into play as a result of the interplay of the interfacial kinetics with ohmic losses and transport limitations. Hence, for nearly every electron-transfer system that possesses an N-NDR, conditions can be set up under which stable limit cycles exist, and many experimentally observed oscillations could be traced back to this mechanism. Overviews of these experimental systems can be found in Refs. [9, 10, 68], Here we compile only a few examples. Figure 13 shows experimental cyclic voltammograms of the reduction... 

This brief overview of mass transfer and separation mechanisms involved in ceramic membrane processes will be useful not only for a better understanding of actual operating conditions of ceramic membranes, but also for anticipating future applications. For example, a same microporous membrane can serve theoretically as liquid or gas separation membrane. However, transport mechanisms and operating conditions being totally different, a good membrane permeability and selectivity in the former case cannot be systematically transposed to the second case. 

An overview of the transport mechanisms in porous membranes is given in Table 9.1. 

Most of the data are taken from an overview of Burggraaf [108] which has been updated with results reported later. Some typical results obtained with capillary condensation and/or surface diffusion as transport mechanism are given in Table 9.13. A discussion of these data is given in Section 9.2.S.3. As is shown, interesting combinations of high to very high separation factors with reasonable to good flux values can be obtained. 

In this chapter we present an overview of current research in the field of nonclassical transport-based delivery. Examples of major vectors are described in brief, focusing on applications as well as physical properties such as the vehicles unusual polycationic character. Methods of complexation of cargoes to vectors are also described. In addition, although no consensus has yet been reached regarding the details of the nonclassical transport mechanism, a variety of hypotheses and models are described in detail and evaluated in the context of applicability to general mechanisms of nonclassical transport. 

In this by no means comprehensive overview, we examine the families of bacterial polyspecific transporters and features of their structure and transport mechanisms that make them particularly efficient in preventing antibiotics access to their targets. 

The effects of molecular order on the gas transport mechanism in polymers are examined. Generally, orientation and crystallization of polymers improves the barrier properties of the material as a result of the increased packing efficiency of the polymer chains. Liquid crystal polymers (LCP) have a unique morphology with a high degree of molecular order. These relatively new materials have been found to exhibit excellent barrier properties. An overview of the solution and diffusion processes of small penetrants in oriented amorphous and semicrystalline polymers is followed by a closer examination of the transport properties of LCP s. 

Kosoglou T, Vlasses PFI. Drug interactions involving renal transport mechanisms an overview. CICP Ann Pharmacother 1989 23 116-22. 

Beonnee F (1989) Renal calcium transport mechanisms and regulation - an overview. Am J Physiol 257 F707-711. 

This chapter focuses on the use of ILs as solvent for organic compounds and metal extraction. An overview of the recent advances in this field in IL extraction technology is given, including issues such as L-L extraction and ILMs for metal ions and organic compounds, transport mechanisms, configurations, stability, and fields of application. 

The major application of DC electroosmotic flow in micro-and nano-fluidics continues to be as a general transport mechanism in Lab-on-Chip type devices. Specific applications along these lines are too numerous to mention here and thus interested readers should consult any one of a number of recent review articles (e. g. Erickson et al. [6]) for more details. Rather we provide a brief overview of a select number of key research findings with regards to non-traditional emerging technologies involving electroosmotic effects for micro- and nanosystems. 

The 27 chapters of this book describe separations of metal ions, anionic species, organic molecules, and gas mixtures that involve liquid membrane processes. Scientists and engineers in academic, governmental, and industrial laboratories in eight countries contributed to this volume. An overview chapter provides an introduction to the various liquid membrane configurations, transport mechanisms, and experimental techniques. A tribute chapter follows, summarizing the many contributions of Norman N. Li in the field of membrane science. The remainder of the book is divided into sections on theory and mechanism (6 chapters), carrier design, synthesis, and evaluation (6 chapters), and applications in... 

Sarrade S., Rios G., Carles M. Dymamic characterization and transport mechanisms of two inorganic membranes for nanofiltration. J. Membr. Sci. 1994 97 155-166 Sastre A.M., Kumar A., Shukla J.P., Singh R.K. Improved techniques in hquid membrane separations an overview. Separ. Purif. Methods 1998 27(2) 213-298 Schaefer D.W. Engineered porous materials. MRS Bull. 1994 19(4) 14—17... 

In this section, we provide an overview of the physical characteristics of nanomaterials that enable them to interact with animal cells and cellular compartments. Because they are chemically stable and relatively inert, 1-D nanostructures (1-D NS) have relatively low cell cytotoxicity (as outlined above), while their chemical modification also provides a means for linkage with specific biomolecules. Thus, 1-D NS may interact directly with cellular substructures. In addition, a typical cellular targeted delivery strategy is also discussed that can support the cellular uptake of these nanoshuctures. Notably, 1-D NS with dimensions of 2 to lOOnm are particularly suited to the adoption of intrinsic cellular transport mechanisms, and can be used for the targeted delivery of specific biomolecules to specific cells and tissues. Moreover, 1-D NS may also provide nanoplatform constructs for the delivery of specific biomolecules through interactions in well-characterized intracellular trafficking pathways. 

Among these mechanisms, viscous flow is non-selective while Knudsen diffusion is selective to smaller molecules. At high temperature, gas adsorption becomes weak and thus the surface diffusion and capillary condensation may be negligible. In fact, the perm-selectivity in micropo-rous membranes is a complex function of the temperature, pressure, and gas composition. Therefore, it is necessary to evaluate the perm-selectivity of the porous membranes using a gas mixture under similar operating conditions [3]. Table 2.2 gives an overview of the transport mechanisms in porous membranes. Note that the perm-selectivity is not always a key factor in MRs. 

For the present, we are concerned with structural materials, and so we shall limit this overview to dielectrics (insulators) and metals. Furthermore, since dielectrics have only one heat transport mechanism (phonons), and metals have two (phonons plus electrons), we shall begin by examining heat transport in dielectrics. 

The purpose of the present chapter is to provide an overview of these distinct and complementary roles of the arachidonate cascade, intracellular and transcellular. We will first consider a series of messenger functions that arachidonate metabolites may serve within cells. We will turn next to the transport mechanisms used by the eicosanoids to exit cells and to gain access to transmembrane receptors present on the surface of cells nearby. Finally, we will briefly discuss the molecular structures of the eicosanoid receptors, their transduction mechanisms and some of their physiological and pharmacological properties. 

In the previous section some relevant transport features of the bioturbation process were described for macrofauna that occupy the upper layers of both soils and sediments. Different modes of bioturbation are possible and model formulations should reflect the various sediment reworking mechanisms. Models developed for benthic organisms in sediment are quite advanced and described in a recent literature review (Thoms et ah, 1995). An overview of those sediment mixing models will be presented in the following section. Although comparable and extensive developments do not exist for soil bioturbation, the similarities in the bioturbation transport mechanisms permit the application of sediment models to describe soil bioturbation. 

Abstract This chapter discusses the research and development of porous ceramic membranes and their application as membrane reactors (MRs) for both gas and liquid phase reaction and separation. The most commonly used preparation techniques for the synthesis of porous ceramic membranes are introduced first followed by a discussion of the various techniques used to characterise the membrane microstructure, pore network, permeation and separation behaviour. To further understand the structure-property relationships involved, an overview of the relevant gas transport mechanisms is presented here. Studies involving porous ceramic MRs are then reviewed. Of importance here is that while the general mesoporous natnre of these membranes does not allow excellent separation, they are still more than capable of enhancing reaction conversion and selectivity by acting as either a product separator or reactant distributor. The chapter closes by presenting the future research directions and considerations of porous ceramic MRs. 

Although blood pressure control follows Ohm s law and seems to be simple, it underlies a complex circuit of interrelated systems. Hence, numerous physiologic systems that have pleiotropic effects and interact in complex fashion have been found to modulate blood pressure. Because of their number and complexity it is beyond the scope of the current account to cover all mechanisms and feedback circuits involved in blood pressure control. Rather, an overview of the clinically most relevant ones is presented. These systems include the heart, the blood vessels, the extracellular volume, the kidneys, the nervous system, a variety of humoral factors, and molecular events at the cellular level. They are intertwined to maintain adequate tissue perfusion and nutrition. Normal blood pressure control can be related to cardiac output and the total peripheral resistance. The stroke volume and the heart rate determine cardiac output. Each cycle of cardiac contraction propels a bolus of about 70 ml blood into the systemic arterial system. As one example of the interaction of these multiple systems, the stroke volume is dependent in part on intravascular volume regulated by the kidneys as well as on myocardial contractility. The latter is, in turn, a complex function involving sympathetic and parasympathetic control of heart rate intrinsic activity of the cardiac conduction system complex membrane transport and cellular events requiring influx of calcium, which lead to myocardial fibre shortening and relaxation and affects the humoral substances (e.g., catecholamines) in stimulation heart rate and myocardial fibre tension. 

The first two volumes in the series New Comprehensive Biochemistry appeared in 1981. Volume 1 dealt with membrane structure and Volume 2 with membrane transport. The editors of the last volume (the present editor being one of them) tried to provide an overview of the state of the art of the research in that field. Most of the chapters dealt with kinetic approaches aiming to understand the mechanism of the various types of transport of ions and metabolites across biological membranes. Although these methods have not lost their significance, the development of molecular biological techniques and their application in this field has given to the area of membrane transport such a new dimension that the appearance of a volume in the series New Comprehensive Biochemistry devoted to molecular aspects of membrane proteins is warranted. 

Although a substantial body of data is available on the levels of linear alkylbenzene sulfonates (LASs) in rivers and estuaries, fewer studies have been conducted on their environmental behaviour, with reference to the mechanisms involved in their transport and to the reactivity they undergo. Studies of LAS in subterranean water and in the marine medium are scarce and have mainly been conducted in the last decade [2-6], coinciding with the development of new techniques of concentration/separation and analysis of LAS at ppb levels or less. Data on concentrations of sulfophenyl carboxylates (SPCs) are very scarce and the behaviour of these intermediates has hardly received any study. This chapter provides an overview of the current knowledge on behaviour of LAS and their degradation products in coastal environments. 

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