Stratum granulosum

1c Stratum Granulosum. The next layer down is the stratum granulosum, 

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The epidermis consists of several types of cells. The epidermal cell type apposed to the dermis is the stratum germinativum (basal cell layer), over which are the stramm spinosum, stratum granulosum, stratum ludicum, and the outermost layer or stratum corneum. The basal cell layer consists of one layer of columnar epithelial cells. On division, the basal cells are pushed up and become the stratum spinosum, which consists of several layers of cells. As these cells approach the surface of the skin they become larger and form the stratum granulosum. 

Further work found that the formation of acidic microdomains occurs at the stratum granulosum-SC interface and is regulated by the sodium-proton exchanger NHEl. In addition, the acidic SC surface is not fully developed at birth, and rather acidic microdomains at the SC-SG interface develop postnatally (Behne et al. 2003). Niesner et al. also used TP FLIM on artificial skin constructs and found that an identical pH gradient to that found in mammalian skin exists, which could enable further research on barrier function without the need for human or animal tissues (Niesner et al. 2005). 

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. 

Epidermis can be divided into stratum basale (SB), stratum spin-osum (SS), stratum granulosum (SG), and stratum corneum (SC). The epidermal cell layers are interconnected by desmosomes.45,48 A cross section of the skin epidermis is shown in Fig. 2.4. 

There are slight, but obvious variations in the elemental distribution patterns from one section to another, although a general trend can clearly be discerned. The Fe and Zn distributions have their centers of gravity in the stratum spinosum/stratum granulosum area, but Zn is more clearly confined to the basal layer. 

Ca shows a twofold or even higher increase in the stratum granulosum region compared to normal skin, but in contrast to the Ca distribution in normal skin, that of psoriasis follows the mass distribution more closely. In many sections there is an additional Ca peak in the vicinity of the basal cell layer, but the full significance of this is not clear. 

FIGURE 6.1 Illustration of calcium gradient in epidermis based on literature data (proton induced x-ray emission analysis of calcium in sectioned human skin) (Malmqvist et al., 1987). SB, stratum basale/basallayer SS, stratum spinosum SG, stratum granulosum SC, stratum corneum. 

FIGURE 6.2 Illustration of skin barrier repair in epidermis. SC, stratum corneum SG, stratum granulosum TEWL, transepidermal water loss ELS, epidermal lipid synthesis. 

Results from enzymologic studies have suggested that SCCE has an extracellular localization in the stratum corneum.45 This has been corroborated by means of immunoelectron microscopy. With this method SCCE was found intracellularly in association with lamellar bodies in the stratum granulosum. In the transition between the stratum granulosum and the stratum corneum, SCCE is extruded to the extracellular space together with the lamellar bodies. In the stratum corneum specific labeling is found only in the extracellular space, often in association with corneodesmosomes.46... 

Scanty or absent stratum granulosum Fligh CS/low free cholesterol + ... 

Is normally present in stratum granulosum and stratum corneum... 

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