Horny cells

It is not yet clear whether the calcium gradient leads to the formation of a mature barrier or the barrier caused the gradient. It may even be both, if the regulation uses a feedback mechanism, as the differentiation will eventually form a barrier leading to the accumulation of calcium ions in the upper epidermis. This high level of calcium will, in turn, guarantee the ongoing process of differentiation toward the formation of corneocytes (horny cells in the SC). The mechanism is thus almost completely autonomous, perpetual, and, if it runs smoothly, requires little correction from the body. 

It is to be emphasized that, structurally, the horny cell is very simple, containing essentially nothing more than filaments and matrix.. . . This dense and total fibrous packjing would pffer tremendous resistance to... 

The term hydration dermatitis refers to the important role of water in the development of irritant dermatitis [15]. Water penetrates the stratum corneum barrier, is retained in the horny cells and increases by swelling the thickness of the stratum corneum by a factor 4 to 6. After exposure, the water gradually evaporates. By means of this alternating process of swelling and shrinking, cytokines are released. Inflammation is induced and the proliferation and differentiation of the keratonocytes is disturbed, further impairing the... 

Yamazaki, K. Fujiwara, N. Seto, T. Yang, P. Horny cell-staining liquid, and homy cell-staining method. PCX Int. Appl. WO 2007029437,2007 Ghent. Abstr. 2007, 146, 312248. 

Figure 7.3C Portions of several normal horny cells, showing the speckled appearance produced by the filaments in transverse section (x33 440)...

After 4 years treatment on a chlorophyll-free diet, the second patient showed clinical improvement with a decrease in ichthyosis. The epidermis had a granular layer 3 cells thick. In the basal layer there were lipid droplets and the oil red O stain was negative. Ultrastructurally the granular layer had three cell layers with slightly decreased amounts of keratohyalin which is structurally normal. The stratum corneum consisted of 20 to 25 flat horny cells (Figure 9.3). In the lower epidermis few liposomes were present in the keratinocytes. 

Figure 10.4 Ichthyosis congenita (lamellar ichthyosis), (a) Survey of the granular layer and lowermost horny cells x4 000. (b-d) Lipid droplets (L) in the horny layer xSOOO (b), and x40 000 (c and d)...

Figure 10.5 Sjogren-Larsson s syndrome, (a) Parakeratotic horny cells, no lipid inclusions present (b) straight arrangement of tonofibrils (T) in a transitional cell x33 000...

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... 

Gender, too, affects the appearance of human skin. Nevertheless, there is little evidence that the skin of males and females differs greatly in permeability. However, there are established differences in the barrier properties of skin across the races of humans. While the horny layers of Caucasians and Blacks are of equal thickness, the latter has more cell layers and is measurably denser [30]. As a consequence, black skin tends to be severalfold less permeable [30,31],... 

The second stage of steeping is the sulfur dioxide diffusion stage in which sulfur dioxide diffuses with the water into the corn kernel through the base end of the tip cap and moves through the cross and tube cells of the pericarp to the kernel crown and then slowly into the horny endosperm. The second stage is diffusion limited because of the specific path required for water going into the kernel. 

The other major route of chemical hazards to plant workers is penetration through the skin, which has a surface area of about 1.8 m for a male adult, and is lined with a tough horny layer of densely packed cells without nuclei. So the skin is reasonably impervious to the penetration of chemical substances, and penetration depends on the lipid solubility of the compound, where the diffusion speed is inversely related to molecular weight. Skin penetration hazard becomes relatively more important than breathing for high boiling point liquids, which have lower vapor pressures. 

Arsenious oxide in dilute solution is not absorbed by the unbroken skin, but absorption occurs from concentrated solution.6 The action is not directly on the cells of the horny layer of the epithelium, but primarily on the capillaries.7... 

FIGURE 12.1 Penetration enhancer activity, (a) Action at intercellular lipids. Some of the ways by which penetration enhancers attack and modify the well-organized intercellular lipid domain of the stratum comeum. (b) Action at desmosomes and protein structures. Such dramatic disruption by enhancers (particularly potent solvents) as they split the stratum corneum into additional squames and individual cells would be clinically unacceptable, (c) Action within comeocytes. Swelling, further keratin denaturation and vacuolation within individual horny layer cells would not be so drastic but would usually be cosmetically challenging (see Menon and Lee [69] for further details). (Reproduced from Barry, B.W., Nat. Biotechnol. 22, 165, 2004. With permission.)... 

B15. Beschomer, R., Horny, H. P., Petruch, U. R., and Kaiserling, E., Frequent expression of haemopoietic and non-haemopoietic antigens by reactive plasma cells An immunohistochemical study using formalin-fixed, paraffin-embedded tissue. Histol. Histopathol. 14, 805-812 (1999). 

Several classes of ceramides have been described in human skin.14 Today it is considered that the ceramides are essential for the barrier properties. It has been suggested that the lower amount of ceramides found in stratum corneum in atopic dermatitis26,27 explains the increased TEWL seen in dry atopic skin. In this context it is of special interest to note that part of the long-chain ceramides of the horny layer are covalently bound to the proteins forming the corneocyte envelope.25 This suggests that such lipids constitute anchors of the hydrophobic phase to the corneocytes and thereby add to the cohesion of the cells of the horny layer. 

In the initial studies of trace elements of human skin cross sections, a Ca profile evolved which was increasing from the basal, germinative level of the epidermis toward the horny layer. The drastic concentration drop of Ca concentration down to threshold values at the border of the stratum germinativum and the stratum corneum was a particularly interesting feature.15-17 Only a few years later this finding could be correlated to the fact that a Ca concentration >0.1 mmol was essential if a fully cornified stratum corneum was to be obtained in cell culture. This relationship between Ca and terminal differentiation of the epidermal cells was verified in a PIXE study of epidermal cell cultures.18... 

The method of Koyama et al.12 was used to determine the parakeratotic index of SC. A glass plate was attached to the skin with Scotch tape (Sumitomo 3M, Tokyo, Japan) measuring 25 x 19 mm to remove corneocytes. The adherent horny material was stained with hematoxylin-eosin solution for microscopic inspection of nuclei. The results were scored depending on the number of the nucleated cells in the visual field (0 = none, 1 = small, 2 = relatively large, 3 = very large). 

Figure 9.2 Section of steeped corn horny endosperm (1 Op,m thick, iodine stained, magnified X612 SG, starch granules PM, protein matrix CW, cell wall).

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