Epidermis-keratinocytes, layers

The mode of action of glycerol both on SC hydration and epidermal barrier function seems to be related to the aquaporin-3 (AQP3) channel. The basal layer of epidermal keratinocytes contains AQP3, a small membrane protein that functions as a facilitated transporter of water and glycerol.11 Glycerol is transported very slowly into the epidermis and thus its transport rate is sensitive to the intrinsic glycerol permeability of the basal keratinocyte layer. 

Figure 7. Fluorescence image of the epidermis of a neonatal mouse that received 500 mg kg ALA intraperitoneally for 4 h. Vertical sections of the skin were imaged by CLSM. The fluorescence image is aligned with a schematic representation of the epidermal stratification. The green dotted line represents the basal membrane. Red fluorescence can be seen in the membranes of the viable keratinocytes. There is stronger fluorescence in the more differentiated (higher) keratinocyte layers than in the basal layer.

In Fig. 2.16 it shows the skin composition in layers, the stratum comeum, granular, spinosum, and basal. The epidermis uppermost layer, the stratum comeum, has keratinocytes tightly linked by des-mosomes in a hydrophobic cellular matrix. This sfructure CTeates an anatomical barrier against irritants, alleigens, and shear force. In addition to the physical barrier, there are mediators of resistance such as leucocytes, cytokines, complanent cascade, and host defense peptides [AMPs]. 

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 most superficial layer of skin is the stratum comeum (SC), which consists of terminally differentiated keratinocytes (comeocytes) that originate from actively proliferating keratinocytes in lower epidermis (basale, spinosum, and granulosum cells), and contain a lamellar lipid layer secreted from lamellar bodies (Fig. 7a). Flydration of the SC is an important determinant of skin appearance and physical properties, and depends on a number of factors including the external humidity, and its structure, lipid/protein composition, barrier properties, and concentration of water-retaining osmolytes (natural moisturizing factors, NMFs) including free amino acids, ions, and other small solutes. 

Mammalian skin must be tough, water-resistant, self-renewing, and rapidly healing. The outer layers of cells or epidermis consist principally of keratinocytes, epithelial cells specialized for formation of keratin (Fig. 7-31). In the inner layer of the epidermis the basal stem cells divide, providing a constant outward flow of cells which become progressively flattened, dehydrated, and filled with keratin fibrils.3 The outer layers contain only dead cells which are finally sloughed or abraded from the surface. Human epidermis is completely renewed in about 28 days ... 

The stratum granulosum is the most superficial cell layer of the viable epidermis and contains highly differentiated keratinocytes. The lamellar bodies, which have been formed in the stratum spinosum, migrate to the apical periphery of the uppermost granular cells and eventually fuse with the membrane of the keratinocyte. Via exocytosis their content is extruded into the intercellular spaces at the stratum granulosum-stratum corneum interface. The lipids derived from the lamellar bodies are essential for the formation of the stratum corneum barrier. 

Yokota, K., and Sawamura, D., 2006, Hailey-Hailey disease with affective disorder Report of a case with novel ATP2CI gene mutation. J. Dermatol. Sci. 43, 150-151 Yoshida, M., Yamasaki, K., Daiho, T., Iizuka, H., and Suzuki, H., 2006, ATP2C1 is specifically localized in the basal layer of normal epidermis and its depletion triggers keratinocyte differentiation. J. Dermatol. Sci. 43, 21-33... 

Epidermis. The epidermis is a 50- to lOO-pm-thick layer made of ker-atinocytes that migrate outward from the basal cell into highly differentiated nondividing cells.46,47 During differentiation, keratinocytes transform from polygonal (cuboidal) cells to spinous (prickly) cells, flattened granular cells, and finally to flattened polyhedral dead corneocytes full of the protein keratin.45,47... 

Fig. 12.3. Epidermal measurements, mitotic figures, and apoptotic keratinocytes in a chronic proliferative dermatitis mutant (Sharplncpdm/Sharplncpdm) mouse. Routine hematoxylin- and eosin-stained paraffin histologic sections can be used to determine proliferation rates based on mitotic index (number of mitotic figures, circled in the figure, in the stratum basale per 1000 cells) or the presence and numbers of apoptotic epidermal keratinocytes (dotted arrows) when present. Epidermal thickness can be measured at high dry magnification (40x) to include the malpigian, living cell, layer (M), the stratum corneum thickness (SC), or the full thickness of the epidermis (M+SC).

Although the physiological function of IL-20 has not been identified, three lines of evidence support a role for IL-20 and its receptor in inflammatory skin diseases such as psoriasis. For example, overexpression of IL-20 in transgenic mice results in neonatal lethality with skin abnormalities similar to those observed in human psoriatic skin (Bll). These include several hallmark characteristics of this multigenic diseases such as increased proliferation of keratinocytes in the basal and the suprabasal layers of the epidermis, aberrant epidermal differentiation, and infiltration of immune cells into the skin (R3). Recombinant IL-20 protein... 

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