Epidermis general structure

All of these structures have an epithelial lining that lies at the interface as well as extracellular matrix including basement membranes and loose connective tissue that supports the cellular layers (Table 3.2). These tissues are similar in their general structure they all have an inner cellular layer, supportive connective tissue, and an outer cellular layer. It is important to be familiar with the structure of these tissues to be able to analyze how external and internal mechanical forces are transduced at both the macroscopic and microscopic level into and out of cells. The effect of mechanical loading on these tissues is complex, but as discussed above, with increased frictional forces on the epidermis, the surface layer of skin actually increases the thickness of the epidermis. 

Wool. Wools and the hair of animals in general appear under the microscope (Fig. 84, Plate VIII) to consist, in their normal and complete structure, of three layers, namely a central medullary canal, surrounded by a layer of very thin fibrillary cells, the latter being enveloped by wide, scale-like cells, which form the cuticle or epidermis. 

Microscopically, the skin is a multilayered organ composed of many histological layers. It is generally subdivided into three layers the epidermis, the dermis, and the hypodermis [1]. The uppermost nonviable layer of the epidermis, the stratum corneum, has been demonstrated to constitute the principal barrier to percutaneous penetration [2,3]. The excellent barrier properties of the stratum corneum can be ascribed to its unique structure and composition. The viable epidermis is situated beneath the stratum corneum and responsible for the generation of the stratum corneum. The dermis is directly adjacent to the epidermis and composed of a matrix of connective tissue, which renders the skin its elasticity and resistance to deformation. The blood vessels that are present in the dermis provide the skin with nutrients and oxygen [1]. The hypodermis or subcutaneous fat tissue is the lowermost layer of the skin. It supports the dermis and epidermis and provides thermal isolation and mechanical protection of the body. 

It is important to understand the structure of insect cuticle before we study the cuticu-lar penetration of insecticides. Figure 6.1 shows the structure of insect integument. The integument is the outer layer of the insect, comprising the epidermis and the cuticle. The epicuticle is generally about 1 micron in thickness. It can be composed of as many as four sublayers the cement layer (outermost), the wax layer, the polyphenol layer, and the cuticu-lin layer. The epicuticle, which makes up about 5% of the total thickness of the cuticle, contains lipids, lipoprotein, and protein and, therefore, it is lipophilic. Beneath the epicuticle lies the procuticle, which comprises the exocuticle and the endocuticle. This is essentially a hydrophilic chitin-protein complex containing considerable quantities of water. The endocuticle is soft and is the major constituent of larvae and soft-bodied insects. It is composed of microfibers of chitin and protein, which may impart elasticity to the cuticle. Above this section, the exocuticle is predominant in hard-bodied insects and forms most of the cuticle in adult beetles. It is present only as a thin layer in many larvae and in the hard parts of... 

The most metabolic activity of plants is carried out in the tissue called parenchyma, which generally makes up the bulk of the volume of all soft edible plant structures. The epidermis, which sometimes is replaced by a layer of corky tissue, is structurally modified to protect the surface of the organ. The highly specialized tissues collenchyma and sclerenchyma provide mechanical support for the plant. Water, minerals, and products of metabolism are transported from one part to another of the plant through the vascular tissues, xylem and phloem, which are the most characteristic anatomical features of plants on the cross section. 

The skin is a multi-layered (veneered or stratified) structure comprising three principal layers, i.e. the epidermis, dermis (corium) and hypoder-mis (Figure 2). Human skin can be divided into two types - glabrous and non-glabrous. The former is mainly limited to the palms of the hand and soles of the feet (palmar-plantar skin) and comprizes a stratum corneum which is generally thicker and less permeable than non-glabrous skin. 

In epidermolysis bullosa simplex, the skin blisters in response to a very slight mechanical stress. The familial form of the disease is generally caused by mutations in either of the two forms of keratin that constitute the keratin heterodimers of the basal layer of the epidermis. The weakened keratin cytoskeleton results in cytolysis when stress is applied. The disease also can be caused by mutations in plektin, the protein that attaches keratin to the membrane protein integrin in hemidesmosomes (a structure involved in attaching cells to the extracellular matrix). 

The studies add more, perhaps, in the field of protein structure, than to knowledge of the epidermis or of epithelia in general. But what contribution there is of the latter kind is of importance, since our knowledge of the epidermis at the molecular level is so very small. 

Electron microscopic observations have shown that the cells of isolated gastrula ectoderm after some days in culture develop in their periphery a zone which contains vacuoles and in some cells the basal bodies of cilia. These are the same structures as found in epidermis. They are not found in the ectoderm, which was induced by the vegetalising factor. Obviously gastrula ectoderm is already determined to special pathways during differentiation, but its developmental fate can still be changed. In ectoderm treated with actinomycin D the vacuolar zone is retarded in its development (Grunz, 1973). A more general problem is raised by these experiments. Obviously, the induction of the ectoderm leads not only to an acquisition of new properties but also to a loss of properties which would have been expressed in the uninduced ectoderm. 

Leica IMKXIO data archiving software. The observations of general morphology are carried out on paraffin slices dyed with Masson s trichrome, Goldner variant. Cellular structure alterations are searched for in the four main skin layers (i.e., superficial and basal epidermis, papillary and reticular dermis). 

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