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Epidermal keratinocytes are the epithelial cells of mammalian skin. At the basal layer of the epidermis, these cells proliferate strongly, and as they move towards the skin surface, differentiation proceeds. At the uppermost layer of the epidermis, keratinocytes undergo apoptosis and die, forming a thin, water-impermeable layer called the stratum corneum. Peripheral blood vessels do not reach the epidermis, but peripheral nerve fibers do penetrate into it. Until recently, it was considered that the main role of epidermal keratinocytes was to construct and maintain the water-impermeable barrier function. However, since the functional existence of TRPV1, which is activated by heat and low pH, in epidermal keratinocytes was identified, our understanding of the role of keratinocytes has changed enormously. It has been found that many TRP channels are expressed in epidermal keratinocytes, and play important roles in differentiation, proliferation and barrier homeostasis. Moreover, because TRP channels expressed in keratinocytes have the ability to sense a variety of environmental factors, such as temperature, mechanical stress, osmotic stress and chemical stimuli, epidermal keratinocytes might form a key part of the sensory system of the skin. The present review deals with the potential roles of TRP channels expressed in epidermal keratinocytes and focuses on the concept of the epidermis as an active interface between the body and the environment. [ABSTRACT FROM AUTHOR]

In recent years, several groups have succeeded in extending single-molecule microscopy technology to the level of a living vertebrate organism using the zebrafish embryo as a model system. In this chapter an overview will be presented of these studies and three lines of research will be discussed. First, work will be presented in which fluorescent proteins have been imaged at the single-molecule level in the epidermis of zebrafish embryos using total internal reflection fluorescence (TIRF) microscopy. Second, investigations will be presented in which individual quantum dots have been imaged in zebrafish embryos by selective plane illumination microscopy (SPIM). Third, studies will be discussed in which fluorescence correlation spectroscopy (FCS) has been applied to fluorescent proteins in zebrafish embryos. All three research lines show discrepancies between results obtained in zebrafish embryos and data obtained in cell cultures, illustrating the relevance of performing these studies in an in vivo model. [ABSTRACT FROM AUTHOR]

The integument of adult Hirsutiella zachvatkini and Euschoengastia rotundata (Trombiculidae), Platytrombidium fasciatum and Camerotrombidium pexatum (Microtrombidiidae), Piona conglobata (Pionidae), and Teutonia cometes (Teutoniidae) (water mites) were investigated by transmission and scanning electron microscopy. The soft integument of adult trombiculids is built up of specific epithelial respiratory tissue, provided by long, branched mechanoreceptor setae organized as neotrichia functioning as a plastron. The seta pits with clear cuticle are surrounded by cuticular folds with tightly packed ridges composed of an electron-dense substance. The underlying epidermal tissue is formed of separately scattered compact epidermal cells intermingled with large polymorphic so-called `intra-epithelial cells` with clear cytoplasm devoid of organelles. The integumental folds with the intra-epithelial cells filled with metabolic and sorptional water are thought to function as air gills, which selectively absorb and transport oxygen from the outside to internal tissues. In microtrombidiids, also an internal cuticular meshwork is expressed, formed of thick electron-clear strands immersed into the epidermis and crossing at right angles. This meshwork is separated from the external cuticle, comprising a thick lamellar procuticle covered by thick electron-light epicuticle. Flat uniform epidermal cells contain numerous pigment granules. In water mites, a very thick lamellar procuticle penetrated by pore canals is covered by a thick dense epicuticle. Setae are arranged following the orthotrichous type. The epidermal layer underlying the cuticle consists of flat uniform epithelial cells devoid of pigment. The organization of the integument in stocks of Trombiculoidea and Trombidioidea appears strongly apomorphic, whereas it is plesiomorphic in water mites. [ABSTRACT FROM AUTHOR]

The article provides information on the entry of immunotoxic agents into the body. It is a result of breaching the natural barriers of skin and mucosal epithelia. The epithelia of the skin and mucus membranes are involved in exclusion of substances. Langerhans cells found in the epidermis are involved in the processing and presentation of substances that enter the skin.

The article presents an encyclopedia entry for the term contact hypersensitivity. The term is a form of delayed-type hypersensitivity (DTH) or cell-mediated immune reaction that is expressed in the epidermis. Contact hypersensitivity is the most frequent form of DTH reaction and the most prominent clinical manifestation of a type IV immune reaction, but is also part of immediate contact dermatitis, according to type I immune reactions.

A definition of the term "melanoma" is presented. It refers to a tumor arising from melanocytes. Melanocytes are dendritic cells that migrate from the neuroectoderm to lodge at the base of the epidermis and in other epithelial sites which include the eye, gastrointestinal tract and vagina. It can also arise at any of the sites, but most commonly arises in the epidermis.

An abstract of the article "Structural and Immunocytochemical Characterization of Keratinization in Vertebrate Epidermis and Epidermal Derivatives," by Lorenzo Alibardi is presented.

A definition of the term "impetigo contagiosa" is presented. It refers to the infection of the epidermis with Streptococcus pyogenes and less frequently with Staphylococcus aureus.

A definition of the term "epidermis" is presented. It refers to the superficial layer of the skin, which provides the first barriers of protection from the invasion of foreign substances into the body. It is subdivided into five layers namely, stratum germinativum, stratum spinosum, stratum granulosum, stratum lucidum and stratum corneum.

A definition of the term "epidermal cells" is presented. It refers to cells in the epidermis, including keratinocytes, Langerhan cells, melanocytes and Merkel cells.

The article presents an encyclopedia entry for dermis. The dermis functions as a thermoregulator and it supports the vascular network to supply the avascular epidermis with nutrients. A papillary dermis and a reticular layer are the two zones of dermis. It contains fibroblasts and its immune cells are also present that are involved in defense against foreign invaders passing through the epidermis.

The article presents an encyclopedia entry for cornifying or cornification of cells. The process starts in the upper spinous layer of the epidermis and predominantly depends on the intracellular calcium ion level. The cornification process of keratinocytes occurs in the formation of cornified cell envelopes and is accompanied by degradation of cell organelles.