Epidermis, transport through

Figure 2 Three possible routes of solute ion transport through epidermis during iontophoresis.

Penetration of water and low molecular weight nonelectrolytes through the epidermis is proportional to their concentration, and to the partition coefficient of the solute between tissue and vehicle. A form of Pick s law describes steady-state transport through the skin ... 

The acquisition of iron, copper, and zinc in plant roots has been described in Chapter 7. Once within the root epidermal cell, the iron must be transported through the roots to the xylem and thence to the leaves, and this intercellular metal transport is illustrated for dicots in Fig. 8.8 and for monocots in Fig. 8.9. In dicots, Fe, Zn, and Cu are taken up into the symplast by transporters in the epidermis. Reduction of Fe and possibly of Cu by FR02 and acidification of the soil by an Arabidopsis ATPase contribute to increased metal uptake. Metals can then travel through the symplastic space to the vasculature. Transport into the xylem is still not fully characterised. In the case of Fe, it is probably as citrate, and the citrate transporter FRD3 has been shown to efflux citrate into the xylem and is required for Fe transport to the shoot. Zn and Cu are thought to be effluxed into the xylem by... 

Exclusively submicron particles obtained by high pressure homogenization were used in a study which compared skin interaction of GMO-based cubic nanoparticles (with additional vesicular structures as observed by cryo-TEM) with that of other lipidic nanoparticles with compact liquid, crystalline or thermotropic liquid crystalline matrix structure. The cubic nanodispersion, which was stable with respect to particle size for 15 months of storage at room temperature, increased skin permeation of the model substance corticosterone (used in trace amounts in this study) compared to the other types of lipid nanoparticles. Permeation from all lipidic dispersions was, however, lower than from an aqueous solution which was attributed to the retention of a certain fraction of the drug in the lipid nanoparticles. Considering only the drug present in the aqueous phase of the dispersion as available for transport through the epidermis, the presence of cubic GMO particles increased permeation by the factor 2.4. 

First, consider the transepidermal route. The fractional area of this route is virtually 1.0, meaning the route constitutes the bulk of the area available for transport. Molecules passing through this route encounter the stratum corneum and then the viable tissues located above the capillary bed. As a practical matter, the total stratum corneum is considered a singular diffusional resistance. Because the histologically definable layers of the viable tissues are also physicochemically indistinct, the set of strata represented by viable epidermis and dermis is handled comparably and treated as a second diffusional resistance in series. 

Rastogi, S.M., and J. Singh. 2001. Lipid extraction and transport of hydrophilic solutes through porcine epidermis. Ini J Pharm 225 75. 

As outlined above, fluid-state PCs penetrate through stratum corneum to the epidermis. In this process, those molecules that are embedded in the PC matrix get transported along. For long it has been thought that a prerequisite for a successful penetration is the encapsulation of the drug substance into a PC liposome. This assumption has been challenged recently.33... 

In the past decade a number of physical techniques have been used to evaluate the unique barrier properties of mammalian skin [1]. This chapter deals with the use of another physical technique, fluorescence spectroscopy, to study the barrier properties of the human stratum corneum (SC), specifically with respect to the transport of ions and water. The SC is the outermost layer of the human epidermis and consists of keratinized epithelial cells (comeo-cytes), physically isolated from one another by extracellular lipids arranged in multiple lamellae [2]. Due to a high diffusive resistance, this extracellular SC lipid matrix is believed to form the major barrier to the transport of ions and water through the human skin [3-5]. The objective of the fluorescence studies described here is to understand how such extraordinary barrier properties are achieved. First the phenomenon of fluorescence is described, followed by an evaluation of the use of anthroyloxy fatty acid fluorescent probes to study the physical properties of solvents and phospholipid membranes. Finally, the technique is applied to the SC to study its diffusional barrier to iodide ions and water. 

The most metabolic activity of plants is carried out in the tissue called parenchyma, which generally makes up the bulk of the volume of all soft edible plant structures. The epidermis, which sometimes is replaced by a layer of corky tissue, is structurally modified to protect the surface of the organ. The highly specialized tissues collenchyma and sclerenchyma provide mechanical support for the plant. Water, minerals, and products of metabolism are transported from one part to another of the plant through the vascular tissues, xylem and phloem, which are the most characteristic anatomical features of plants on the cross section. 

In monocots, Fe and Zn are taken up as phytosiderophore chelates by YSL transporters in the epidermis. Fe can also be taken up by OsIRTI. Metals move through the symplastic space to the vasculature. The citrate effluxer FRDLl is important for loading of citrate into the xylem and subsequent Fe transport to the shoot through the transpiration stream. YSL transporters also may play a role in unloading the xylem into the shoot and the phloem. Fe is unloaded from the phloem by OsYSL2 and OsIRTI into shoot and seed tissue. 

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