Epidermis, skin layer

From an anatomical viewpoint, it is common to classify burns according to the depth of penetration into various skin layers. As seen in Figure 11, skin is composed primarily of a (usually) thin outer layer called the epidermis followed by a thicker dermis. Below the dermis is a layer of subcutaneous fat followed by skeletal muscle. Burns can be characterized according to the deepest layer of tissue penetrated and the depth to which that layer has been affected. In this scheme, two numbers are used to classify a burn the first designates the lowest layer of tissue damaged, and the second the fractional depth to which that layer has been penetrated. Therefore, a 1.5-degree burn is one affecting only the epidermis (skin layer 1) in which half of the epidermis (0.5) has... 

Desquamation Peeling or shedding of the epidermis (superficial layer of the skin) in scales or flakes. 

Mites are responsible for mange or scabies. This dermatitic disease is characterized by itching, alopecia (baldness) and hyperplasia (excessive tissue formation) of the epidermis with consequent scaling off of the superficial skin layers. Rubbing and scratching by the host to relieve the itching can result in deeper wounds which are open to bacterial complications. Psoroptic mange in sheep is particularly destructive and is notifiable in Britain. 

The principal pigment of human skin, hair, and eyes is melanin, which is synthesized in specialized cells, the melanocytes. They lie between the epidermis (outer layer) and the dermis (inner layer) as shown in Box 8-F. Melanocytes originate from embryonic nervous tissue and migrate into the skin by the third month of fetal life. They retain the highly branched morphology of neurons. Persons of different races all have the same numbers of melanocytes but the numbers and sizes of the pigmented melanosomes (Box 8-F) vary as does the content and chemical composition of the melanin.a d Melanosomes not only are found in the dendrites of the melanocytes but are transferred from them into adjacent epithelial cells.6 1... 

Fig. 18.3. A cercaria of Schistosoma mansoni penetrating the skin epidermis. The parasite has traversed the outer skin layer, stratum corneum (SC), and is halfway through the underlying dermis, stratum basale (SB). Movement through these layers is facilitated by proteases, most particularly an elastase, which is secreted from the cercarial acetabular glands. The cercaria is moving, as indicated by the arrow, into the inner skin layers where it will meet and enter a venule.

The second step in the preparation of the skin is the removal of the epidermis and its load of hair by bucking, which involves soaking the skin in a solution of water and lime. Early leather workers used wood ash to produce the lye. The hair usually slips off during or after the soaking, and the unwanted upper layer of skin may be then scraped off. In modem tanneries, this process is done by machines, but traditionally it is accomplished by hand. If the desired end-product is a leather that is not flexible or elastic, then the skin can be left in the lye solution for a prolonged period. This is known as liming. After the hair and upper skin layer have been removed, the skin must be carefully rinsed to get rid of any residual alkalis. 

Transepidermal water loss (TEWL) is a natural occurrence that takes place in the skin layers. TEWL is the result of movement of water from the deep skin layers across the epidermis into the outside atmosphere. It is a tightly regulated process that is controlled by the stratum comeum [9], Occlusive topical bases and devices, such as transdermal patches, block TEWL and cause increased hydration of the skin. Hydration of the skin increases the permeation rates of compounds transdermally. The occluding effect of transdermal patches is an important mechanism that promotes increased diffusion of the compound across the skin into the systemic circulation [10]. 

First-degree bums affect only the epidermis (outer layer) of skin. The bum site is red, painful, dry, and with no blisters such as seen in a mild sunburn. Rarely... 

The organizational structure of the skin layers is diagrammatically represented in Figure 2. The relative thickness of the epidermis and dermis is shown. If the skin layers are drawn in a diagrammatic way, the orderly layers of cells forming the viable (live) epidermis are seen. The dead, dry, scaling cells of the stratum corneum have a structure that is likened to bricks and mortar. ... 

Skin is a heterogeneous, multiple-layer organ. In a typieal dermal absorption study, three biologieal levels are of main eoncem stratum comeum, epidermis, and whole skin (Sehaefer and Redelmeier, 1996). When the skin is exposed to a ehemieal mixture, the skin and the medium of the chemical mixture form an absorption system. For the three skin layers, three absorption systems could be generated for a given chemical mixture, which will provide abundant information on the three biological levels. 

Understanding growth and maturation is important for skin regeneration, for example. In the adult mammal, an epidermis (the top skin layer) lost through injury regenerates spontaneously... 

Figure 12.15 Formation of the lipid barrier of human skin. The top layer of the epidermis called stratum corneum is a hornified and inert barrier. Its primary functions are regulation of the skin s moisture content and protection of the underlying tissues against external influences. Due to its structure it is often compared to a brick wall in which the non-viable keratin-filled corneocytes are embedded like bricks in a matrix of intercellular lipids. Synthesis of the stratum corneum lipids starts in deeper skin layers, where lipids (mainly glucosylceramides and sphingomyelin) are produced and packaged in so-called lamellar bodies . During differentiation and maturation, these lipids are enzymatically converted to ceramides and finally assembled into densely packed lamellar structures surrounding the corneocytes and filling the intercellular spaces of the stratum corneum.

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