Stratum spinosum

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. 

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. 

The stratum spinosum layer contains abundant desmosomes, lipid lamellar bodies (Odland bodies), keratinosomes, and membrane-coating granules (MCGs). Lipid lamellar bodies are parallel stacks of polar lipid-enriched disks enclosed in a trilaminar membrane.48 The lamellar bodies also contain hydrolytic enzymes capable of converting polar lipids such as glycolipids and phospholipids to nonpolar products such as ceramides and free fatty acids, respectively.46,49... 

FIGURE 5.2 STEM x-ray spectrum from a skin sample.4 Note that there is a conspicuous shift in the Na/K ratio moving from the dermis into the basal cell layer. Again, moving into the stratum spinosum, Na increases and K is lowered, a ratio shift, which suggests that the spinosum cells are incapable of entering the mitosis cycle. 

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. 

The Zn content of the uninvolved psoriatic skin is increased in the stratum spinosum especially, except in one single section where the Zn follows suit with Fe distribution. Such variations are likely to occur as a function of the cell cycle position of a particular cell. 

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. 

Epidermis Stratified squamous epithelium Stratum corneum Stratum spinosum Stratum basale Basement membrane Provides resistance to shear injury... 

Stratum Corneum Stratum Spinosum Stratum Basale... 

Figure 3.7. Structure of skin. Skin is composed of two layers the dermis and epidermis. Epidermis is a stratified squamous epithelium containing stratum corneum, stratum spinosum, and stratum basale (basal cell layer). The dermis contains papillary and reticular layers and a subcutaneous layer containing fat, blood vessels, and skeletal muscle.

Transport of vitamin D3 away from the dermal junction of skin is accomplished by a 52 kDa serum vitamin D-binding protein (DBP). Serum DBP is a member of the a-fetoprotein-albumin super family [36], DBP has high affinity for vitamin D3, but does not bind to its precursors or the products of previtamin D3 side-reactions, lumisterol and tachysterol [37], Accumulation of 7-dehydrocholesterol in skin occurs in sebaceous glands at the malpighian layer of the epidermis, mostly in the stratum spinosum and stratum basal... 

The epidermis consists of five principal layers and is an area of both intense biochemical activity and differentiation. These layers are the stratum comeum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. The stratum corneum (horny layer) is the uppermost layer of the epidermis and the skin. The stratum corneum is composed of dead keratinocytes, which are called corneocytes, and has an abundance of keratin and lipid structures [8], The stratum comeum is considered the rate-limiting barrier for the diffusion of chemical compounds across the skin. The stratum lucidum (clear layer) is composed of two to three layers of dead flattened keratinocytes which appear translucent under a microscope and are present only in thick glabrous skin. 

The stratum spinosum (prickly layer) is composed of several layers of keratinocytes which are starting to exhibit histological and biochemical changes that mark the beginning of the differentiation process. The shape of the keratinocytes has become irregular and enzymes responsible for lipid synthesis are present. 

The Army s interim RfD for sulfur mustard is 7 x 10 mg/kg per day. ORNL (1998) calculated that value on the basis of the lowest oral dose of sulfur mustard that produced forestomach lesions (epithelial acanthosis, which is an increase in the thickness of the stratum spinosum of the epithelial tissue of the forestomach) in rats. The lowest-observed-adverse-effect level (LOAEL) for that effect was 0.03 mg/kg per day in a two-generation reproductive study (Sasser et al. 1989a). In that study, male and female rats were administered sulfur mustard for 5 days per week for 15 weeks, daily for 3 weeks, and 4 days per week for 3 weeks. Because of this discontinuous dosing protocol, ORNL adjusted the LOAEL (LOAELajj) to calculate the doses for continuous exposures. That adjustment was done by calculating the total dose administered during the different exposure protocols ... 

An increase in the thickness of the stratum spinosum of the epithelial tissue. 

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