Epidermis structure

Abraham, W., Wertz, P.W., and Downing, D.T., Linoleate-rich acylglucosyl ceramides of pig epidermis structure determination by proton magnetic resonance, J. Lipid Res., 26, 761, 1985. 

Wertz, P.W. Downing, D.T. Glycolipids in mammalian epidermis structure and function in the water barrier. Science 1982, 217, 1261-1262. 

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... 

Collagen fibers are long and thick in the middle dermis but become increasingly fine toward the outer epidermis as well as toward the inner hypodermis. Apart from this structural characteristic, which is common to all animals, the skin of each species has a different and unique morphology that significantly affects its properties (Calnan and Haines 1991). 

Fig. 4 Graphic showing the structural features of a seed coat and endosperm of a radish seed, according to Vaughan and Whitehouse (1971). e, epidermis p, palisade pi, pigment layer al, aleurone layer hi, hyalin layer. 

Bulla (Plural = Bullae) A large blister appearing as a circumscribed area of separation of the epidermis from the subepidemal structure or as a circumscribed area of separation of epidermal cells caused by the presence of serum, or occasionally by and injected substance. 

The stratum corneum consists of separated, nonviable, cornified, almost nonpermeable corneocytes embedded into a continuous lipid bilayer made of various classes of lipids, for example, ceramides, cholesterol, cholesterol esters, free fatty acids, and triglycerides [6], Structurally, this epidermis layer is best described by the so-called brick-and-mortar model [7], The stratum corneum is crucial for the barrier function of the skin, controlling percutaneous absorption of dermally applied substances and regulating fluid homeostasis. The thickness of the stratum corneum is usually 10-25 /an, with exceptions at the soles of the feet and the palms, and swells several-fold when hydrated. All components of the stratum corneum originate from the basal layer of the epidermis, the stratum germinativum. 

Much of the FLS biochemical and structure/fimction analysis has focused on a protein from C. unshiu (mandarin). A cDNA was isolated based on sequence homology to an Arabidopsis FLS EST (153O10T7) and used as a probe to determine regulation of gene expression [92]. Higher expression was observed in young leaf, flower, peel, and juice sac/segment epidermis tissues. Expression decreased with tissue age, as has been observed for citrus CHS, CHI, and F3H [57]. Southern analysis... 

The skin consists of two main compartments, the epidermis, a stratified squamous epithelium, and the underlying dermis, a richly vascularized tissue embedded in a connective tissue matrix (Fig. 41.1). The epidermis consists of multiple layers of keratinocytes, which differentiate into the outermost layer, the stratum corneum. This layer contains the hydrophilic structural... 

The layers of the epidermis. (Adapted with permission from Montagna W and Parakkal PR The Structure and Function of Skin [3rd ed.]. New York Academic, 1974.)... 

The dermis provides a base for the epidermis and contains fibroblasts that elaborate proteins, such as collagens and elastin, which are crucial for the skin s structural integrity. In addition, mast cells, enriched in a variety of proinflammatory substances, play an important role in tissue remodeling, wound healing, and fibrosis. 

Drugs that are used to treat hyperkeratosis, a thickening of the stratum corneum, are called keratolytics. Examples of these agents are salicylic acid, urea, lactic acid, and colloidal or precipitated sulfur. The precise mechanisms by which these agents treat hyperkeratosis are not known. Presumably, a common property is the ability to denature keratin, the major structural protein of the epidermis. Other beneficial effects vary among the different drugs. All of them have antimicrobial or... 

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