Keratinization processes

Zelickson, A. S., Normal Human Keratinization Processes as Demon-... 

Stratum corneum, the outermost layer of mammalian epidermis, functions physiologically as the principal diflFusion barrier to molecules penetrating the skin and as a protective physical barrier to mechanical insults at the skin surface. Data suggest that these functions are critically dependent on the specific morphological and macromolecular organization of the membrane mosaic (16, 17, 18, 19, 20). Thus, alterations of biophysical properties arise from environmental factors acting directly on the membrane or upon the keratinization process, and they affect... 

There are three possible general reasons for the absence of this chain from psoriatic scale. The first is that it is not synthesized. The second is that it is synthesized but then digested away by proteolytic enzyme activity during the abnormal keratinization process. The third is that it is synthesized but then becomes covalently cross-linked during the abnormal keratinization and is thus not extracted by the reagents used. 

Although it is impossible to rule out any of these possibilities, it seems unlikely that the psoriatic cell, which is involved in an accelerated keratinization process with less than normal digestion of the cell organelles would either elaborate an additional cross-link or digest away one of these chains in a specific manner. So the most likely explanation at present is that one chain is not synthesized and there is, in fact, a gross molecular defect in the psoriatic fibrous protein. 

Following this rough classification, some ultrastructural criteria will be presented for the most important types of ichthyoses, even though it is not possible to fully describe the entire keratinization process for each of them. Only those parameters that may serve as diagnostic aids will be discussed. 

Figure 10.2 Schematic drawing of an epidermal cell column summing up the differentiative and synthetic steps of the keratinization process. SB — stratum basale, SS — stratum spinosum, SG — stratum granulosum, SC — stratum corneum. (From Anton-Lamprecht and Schnyder , with kind permission of Springer Verlag Heidelberg)...

Disturbances may occur in each of these stages, induced either by environmental factors or — in the case of the ichthyoses — by mutation of different genes. In many types the resulting error in keratinization is directly demonstrable in the ultrastructural deviations from the normal keratinization process. 

In most recessive types merely quantitative deviations from the normal keratinization process have been found (X-linked recessive ichthyosis, lamellar... 

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