Epidermis thickness

Skin has several protective mechanisms in addition to its thick epidermis that prevent many chemical compounds from penetrating it. Eccrine (sweat)... 

Patients with photodamage can apply a lotion containing 25% glycolic acid for 6 months. In such cases an increase in total skin thickness of approximately 25% was reported, accompanied by an increased thickness of viable epidermis and dermis, an increased content of acid mucopolysaccharides, a greater collagen density and an improved quality of the elastic fibers. This could be defined as self-treatment. 

Level 2 White frosting with areas of erythema showing through.This level of peel is indicative of a full-thickness epidermal peel to the papillary dermis and can be achieved with TCA concentration of >30%.This peel will result in full exfoliation of the epidermis (Fig. 4). 

All humans experience intrinsic aging. Typically, it is characterized by smooth, relatively atrophic, finely wrinkled or lax skin. Histologically, the stratum corneum is normal. However, the epidermis is atrophic and there is flattening of the dermo-epidermal junction. Dermal features include decreased thickness, loss of elastic fibers, and a decrease in the biosynthetic capacity of fibroblasts [i, 2] (Table 15.1). 

Stratum corneum normal thickness (basket weave pattern), epidermis thinned, atrophic, flattened rete ridges... 

We have already stressed the potential importance of lipid-rich membranes in the skin as potential targets for ROS-induced damage and ageing of human skin is morphologically identical to changes found by peroxidative processes (Serri et al., 1977). The involvement of AA metabolites in skin disease, and in particular psoriasis, has been the subject of much recent interest. Studies have included topical and intradermal administrations of AA metabolites, and assay of such products in clinical specimens. Results show that concentration of AA, 12-hydroxy-eicosatetraenoic acid (12-HETE), PG and leu-kotrienes are increased in psoriatic lesions (Hammarstrom etal., 1975 Camp etal., 1983 Brain etal., 1984 Duell et al., 1988) and also that full-thickness epidermis from normal and diseased skin has the enzymatic capacity to convert AA to some of the same metabolites (Hammarstrom etal., 1975, 1979 Camp etal., 1983 Brain etal., 1984 Ziboh et al., 1984 DueU et al., 1988). The biological effect of both 12-HETE and leukotrienes was confirmed by both topical application and intradermal injection, which caused epidermal inflammation and... 

A nominal spatial resolution of 20 pm was set acquiring an echo window 50-ps long. The position of the sensor was moved in steps to cover the thickness of the epidermis (E), the dermis papilare (DP), the dermis reticulare (DR) and the sub-cutis (SC). Using 64 scans per point and a repetition time of 300 ms the total acquisition time per point was 20 s. (b) Comparison of skin profiles measured in the palm of a male ( ) and a female ( ) volunteer. 

Partial-thickness skin loss of the epidermis and/or dermis. 

IA Melanoma in situ (involves only the epidermis layer) 1mm thickness, no ulceration and Clark level3 II or III 100% 100%... 

Let us consider how the skin is structured to better understand how this tissue performs some of its vital functions. Consider the cross section of the skin sketched in Fig. 1. This illustration shows the readily distinguishable layers of the skin, from the outside of the skin inwards the 10 pm thin, fully differentiated, devitalized outer epidermal layer called the stratum corneum the 100 pm thin live, cellular epidermis and the 1000 pm thin (1 mm thin) dermis. Note that all the thicknesses specified here are representative only, for the actual thickness of each stratum varies severalfold from place to place on the body. Dispersed... 

Small full-thickness wounds are closed and sealed off quickly by reconstruction of the epidermis from the edges of the wound. Large full-thickness injuries take too long to heal by this process and require grafting. All such wounds remain highly permeable until covered over again with a healthy, fully differentiated epidermis. 

The corneal epithelium is a stratified squamous epithelium like the epidermis of the skin but is nonkeratinized like other mucosal epithelia such as the intestinal and airway epithelia. Although the corneal epithelium, five to seven cells thick, represents less than 10% of the entire corneal thickness, it provides as much as 99% resistance to the diffusion of small electrolytes such as Na+ and Cl [55-57],... 

Collagen fibers are long and thick in the middle dermis but become increasingly fine toward the outer epidermis as well as toward the inner hypodermis. Apart from this structural characteristic, which is common to all animals, the skin of each species has a different and unique morphology that significantly affects its properties (Calnan and Haines 1991). 

OCT images of plant tissue in the process of its saturation with water are shown in Fig. 3b-3i. It can be seen from this figure that the thickness of the epidermal and palisade layers increase linearly with the time of the plant being in water. The layers reach their maximum thickness as soon as 40 minutes after the plant has been placed in water (Fig. 3g). Correspondingly, during the same time an increase in the volume of cells of the upper epidermal layer situated closer to the surface is observed. Most significantly the cells and the epidermis increase within the first 5-25 minutes (Fig. 3b-3f)... 

The stratum corneum consists of separated, nonviable, cornified, almost nonpermeable corneocytes embedded into a continuous lipid bilayer made of various classes of lipids, for example, ceramides, cholesterol, cholesterol esters, free fatty acids, and triglycerides [6], Structurally, this epidermis layer is best described by the so-called brick-and-mortar model [7], The stratum corneum is crucial for the barrier function of the skin, controlling percutaneous absorption of dermally applied substances and regulating fluid homeostasis. The thickness of the stratum corneum is usually 10-25 /an, with exceptions at the soles of the feet and the palms, and swells several-fold when hydrated. All components of the stratum corneum originate from the basal layer of the epidermis, the stratum germinativum. 

Figure 1.2 Cross sections of (A) full-thickness skin, x 100 (B) dermatomed skin, x 100 (C) heat-separated epidermis, x400 and (D) trypsin isolated stratum comeum, x400. (Images courtesy of Leon Muijs, Biopharmaceutics Pharmaceutical Technology, Saarland University, Germany).

This may be achieved by complete immersion of full-thickness skin in trypsin solution or by placing the heat-separated epidermis for 24 h at 37°C on a filter paper soaked with the enzyme preparation [64, 83]. Other techniques, such as vacuum or chemically induced blistering, stretching, application of staphylococcal exfoliatin, or proteolytic digestion of viable cells, are seldom reported [74, 87-89],... 

The skin consists of a thin outer layer (epidermis) and a relatively thicker inner layer (dermis). The epidermis is approximately 0.1 mm in thickness, whereas the dermis is generally 2-4 mm thick. Dermoepidermal ridges provide a large interface area between the epidermis and dermis. This is of great importance in that the epidermis, which is not vascularized, receives all its nutrients from the blood supply of the dermis. 

Fig. 12. The kinetics of contraction of full-thickness guinea pig skin wounds separate collagen-GAG matrices into three classes. The wound half-life t,/2 is the number of days necessary to reduce the original wound area to 50%. An inactive matrix does not delay wound contraction significantly relative to the ungrafted control and eventually allows formation of a linear scar. An active, cell-free matrix delays wound contraction by about 20 days but eventually allows lull contraction to occur. An active matrix, which has been seeded with a minimal number of skin cells, delays contraction significantly, later arrests it, and eventually induces synthesis of a new dermis and epidermis within an expanding wound perimeter...

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