Epidermal layers of skin

Figure 1.2 Light micrograph depicting the epidermal layers of skin. The stratum basale (SB), stratum spinosum (SS), stratum granulosum (SG), stratum corneum (SC) layers and dermis of skin. 500x...

Actually, neither vitamin D2 nor D3 is present in foods. Rather, foods contain the precursor molecules 7-dehydrocholesterol and ergosterol. In the presence of sunlight, both precursors are converted in the outer, epidermal layer of skin to the active vitamins, hence the nickname for vitamin D, the sunshine vitamin. ... 

Toxic epidermal necrolysis—a life-threatening skin disorder characterized by blistering and peeling of the top layer of skin. 

Alpha hydroxy acids (AHAs) are water-soluble substances and thereby penetrate the outermost epidermal skin layers. In contrast, beta hydroxy acids (BHAs) are lipid (fat) soluble and are capable of penetrating to the underlying layers of skin (the dermis) located 1-5 mm below the surface of the skinJ2 Most AHAs are derived from plant materials and marine sources. Commonly used AHAs include malic acid (found in apples), ascorbic acid (a common ingredient in numerous fruits), glycolic acid (a constituent of sugar cane), lactic acid (a component of milk), citric acid (naturally abundant in citrus fruits), and tartatic acid (found in red wine). A common BHA is salicylic acid (an ingredient in aspirin). 

Dysplasia is a special type of cell adaptation that literally means disordered growth, and it is usually associated with neoplasia or preneoplastic changes. Dysplasia implies a loss in the uniformity of the individual cells and a loss in the normal tissue growth pattern. For example, a dysplastic area involving the epidermal layers of the skin might contain jumbled, atypical epithelial cells with loss of their normal polarity and orderly differentiation. 

Marrow-Tech, Inc. (Elmsford, NY) has also developed a human skin model. Marrow-Tech s skin equivalent consists of (1) a dermal layer of fibroblasts and naturally secreted collagen and (2) an epidermal layer of keratinocytes separated by a dermal-epidermal junction. Whereas Testskin uses bovine collagen, Marrow-Tech s skin model consists solely of human tissue. 

More recent in vitro studies have supported the original conclusions of Smith et al. (1919) in that HD forms a considerable and persistent reservoir within the epidermal layers of human skin (Chilcott et al., 2000) and it is also likely that other lipophilic agents, such as VX, may have similar skin absorption characteristics (Chilcott et al., 2005b). Clearly, the potential formation of a cutaneous reservoir of agent has important implications for the medical management of... 

In the remainder of this chapter, we consider the properties of intermediate filaments (IFs) and the cytoskeletal structures that they form In cells. Intermediate filaments are found in nearly all animals but not In In plants and fungi. The association of Intermediate filaments with the nuclear and plasma membranes suggests that their principal function is structural (Figure 19-31). In epithelium, for instance, Intermediate filaments provide mechanical support for the plasma membrane where It comes into contact with other cells or with the extracellular matrix. In epidermal cells (outer layer of skin) and the axons of neurons (Figure... 

The epidermis Is a tough outer layer of tissue, which acts as a water-tight barrier to prevent desiccation and serves as a protection against abrasion. In epidermal cells, bundles of keratin filaments are cross-linked by filaggrin, an IFAP, and are anchored at their ends to desmosomes. As epidermal cells differentiate, the cells condense and die, but the keratin filaments remain intact, forming the structural core of the dead, keratinized layer of skin. The structural Integrity of keratin Is essential in order for this layer to withstand abrasion. 

The epidermis is a designation of location rather than type of cells. The epidermal layer of vertebrates, which is the outer layer of skin, is usually made up of stratified epithelium with an outer layer of dead cells and an inner layer of growing and dividing cells. The invertebrate epidermis is normally one cell thick and often forms a protective cuticle (Hale et al., 1995). The epidermis of plants is a one-ceU thick tissue that surrounds young roots, stems, and leaves. The epidermal cells (not epithelium) of stems and leaves secrete a cuticle (a protective layer of protein or lipids). 

As nanomaterials may invade living systems by penetrating the epidermal layer of the skin, the handhng of engineered nanomaterials and the use of cosmetic products containing nanomaterials will increase the threat of epidermal exposure. Since large, micrometer-sized particles cannot penetrate healthy skin, their only route is through open wounds and cuts [35]. However, as the size of particles reduces to the nanometer scale, the chance of particle penetration is increased dramatically, and consequently nanometer-sized particles will be more harmful than their micrometer-sized counterparts in the case of skin contact... 

Epidermis The cellular outer layer of skin, about 0.1 mm thick, which protects against moisture loss and infection. An epidermal graft, for example, cultured epithelium or a thin graft removed surgically, requires a dermal substrate for adherence onto the wound bed. The epidermis regenerates spontaneously following injury, provided there is a dermal substrate underneath. 

There are hundreds of topical steroid preparations that are available for the treatment of skin diseases. In addition to their aforementioned antiinflammatory effects, topical steroids also exert their effects by vasoconstriction of the capillaries in the superficial dermis and by reduction of cellular mitosis and cell proliferation especially in the basal cell layer of the skin. In addition to the aforementioned systemic side effects, topical steroids can have adverse local effects. Chronic treatment with topical corticosteroids may increase the risk of bacterial and fungal infections. A combination steroid and antibacterial agent can be used to combat this problem. Additional local side effects that can be caused by extended use of topical steroids are epidermal atrophy, acne, glaucoma and cataracts (thus the weakest concentrations should be used in and around the eyes), pigmentation problems, hypertrichosis, allergic contact dermatitis, perioral dermatitis, and granuloma gluteale infantum (251). 

Emulsion components enter the stratum corneum and other epidermal layers at different rates. Most of the water evaporates, and a residue of emulsifiers, Hpids, and other nonvolatile constituents remains on the skin. Some of these materials and other product ingredients may permeate the skin others remain on the surface. If the blend of nonvolatiles materially reduces the evaporative loss of water from the skin, known as the transepidermal water loss (TEWL), the film is identified as occlusive. AppHcation of a layer of petrolatum to normal skin can reduce the TEWL, which is normally about 4—8 g/(m h), by as much as 50 to 75% for several hours. The evaporated water is to a large extent trapped under the occlusive layer hydrating or moisturizing the dead cells of the stratum corneum. The flexibiHty of isolated stratum corneum is dependent on the presence of water dry stratum corneum is britde and difficult to stretch or bend. Thus, any increase in the water content of skin is beHeved to improve the skin quaHty. 

Epidermal Maturation and Wound Healing. All three PPAR isotypes are expressed during epidermal maturation each isotype has a specific pattern of expression in regard to development and the various layers of the epidermis. An important role for PPARS in the development and/or maintenance of normal skin health is indicated by the presence of defective wound healing in the PPARS-null mouse. 

O Exposure to ultraviolet radiation from the sun is recognized as one of the primary triggers for skin carcinogenesis. Based on their wavelengths, UV radiation is divided into three components UVA (320 00 nm), UVB (280-320 nm), and UVC (200-280 nm).15 UVB accounts for only 5% of the solar radiation that reaches the earth, but it is the primary carcinogenic component in the UV spectrum.15 The following sequence of events describes the process in which UV radiation causes skin cancer (1) UV radiation reaches the earth, and on the skin, it reaches the cells in the epidermal layer (i.e., squamous cells, basal cells, and melanocytes),16 (2) the UV radiation (specifically... 

Let us consider how the skin is structured to better understand how this tissue performs some of its vital functions. Consider the cross section of the skin sketched in Fig. 1. This illustration shows the readily distinguishable layers of the skin, from the outside of the skin inwards the 10 pm thin, fully differentiated, devitalized outer epidermal layer called the stratum corneum the 100 pm thin live, cellular epidermis and the 1000 pm thin (1 mm thin) dermis. Note that all the thicknesses specified here are representative only, for the actual thickness of each stratum varies severalfold from place to place on the body. Dispersed... 

The outermost layer of the skin appearing in the exploded epidermal sketch of Fig. 1(b) represents the stratum corneum (the horny layer). The principal barrier element of the skin, it is an essentially meta-bolically inactive tissue comprised of acutely flattened, stacked, hexagonal cell building blocks formed from once-living cells. These cellular building blocks are... 

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