Skin, about skin, epidermis, dermis, subcutaneous, horny layer


Understanding the Skin structure
	One of the most important aspects of high Skin Care, is to understand the constituents of the skin itself, this learning helps to achieve better results in choosing the correct products for your specific problem or goal and also helps one to treat ones skin better with a more in-depth knowledge and greater understanding. Structure of the Skin Outer layers (a) Epidermis - most superficial (b) Dermis (c) (Hypodermis/Subcutaneous Tissue) Epidermis Five layers Stratum Germinativum (Basal Layer) Stratum Spinosum (Prickly Layer) Stratum Granulosum (Granular Layer) Stratum Lucidum Stratum Corneum (Horny Layer) Stratum Germinativum (Basal Layer) Innermost layer to the Dermis Separated from the underlying Dermis by a basement membrane Cuboidal shaped cells, with large nuclei & distinct cell content, particularly Ribosome's for Keratin production Mitotic activity most evident in this layer, replacing cells in upper layers Approx 14 days for cells to move through this layer As the cells hit the upper part of this layer, they increase the amount of Keratin in them as Keratin granules Melanocytes are scattered throughout this layer which synthesize the black pigment Melanin Stratum Spinosum (Prickly Layer) This second layer is sometimes considered to be part of the st. germinativum. Polyhedral shaped cells held together by intercellular bridges (or prickles) but become flattened towards the top Prominent nuclei and cytoplasmic basophilia indicate active protein synthesis A fibrillar protein aggregates in these cells to form intracellular fibrils known as tonofibrils which converge upon the desmasomes of the prickles. These tonofibrils become more prominent toward the st. granulosum Stratum Granulosum (Granular Layer) Third layer Contains melanocytes and basophilic granules which are thought to be the precursor to Keratin Flattened and diamond shaped cells which are characterized by numerous, dense basophilic granules which crowd the cytoplasm and tend to obscure the tonofibrils Stratum Lucidum Questionable fourth layer which is often so thin that it is sometimes considered not to be a transitional layer between the st. granulosum and the st. Corneum It is so thin that there is debate currently that the layer is an artefact of the electron microscope and doesn’t in fact exist Supposedly most pronounced in the palms of the hands and the soles of the feet Cells show signs of disintegration and have lost their nuclei and organelles Stratum Corneum (Horny Layer) Final layer or the Horny layer Cells are non-nucleated disintegrated, fused, flattened squamous cells which are filled with Keratin fibres (matured Keratin) Little water Forms the protective barrier for the skin As the junctions become interrupted, the cells are desquamated Dermis Contains two layers Papillary Layer which is closest to the Epidermis Reticular Layer Papillary Layer Consists of loose connective tissue with fine Collagen and Elastin fibres Folded into ridges or papillae which extend in to the Epidermis Especially noticeable in the palms and soles (fingerprints) Contains nerve fibres and blood vessels which extend into the folds, supplying the Epidermis which is avascular Rete pegs (?) Reticular Layer No defined boundary between the two layers Contains denser connective tissue and many thick Collagen fibres (Hypodermis) Technically not part of the skin Composed of loose connective tissue and contain lots of Adipose Tissue for metabolism, insulation, Terminology description - colour, shape, number, size, grouping abscess - a localized collection of pus formed by necrosis of tissue atrophy - loss of Epidermis, Dermis or both. Atrophic skin is thin, translucent and wrinkled with easily visible blood vessels cellulitis - a purulent inflammation of the skin and subcutaneous tissue crust - dried exudate (normally sebum, blood or pus) on the skin surface ecchymosis - a macular red or purple haemorrhage, more than 2mm in diameter, in the skin or mucous membrane erythema- redness of the skin due to vascular dilation excoriation - a superficial abrasion, often linear, which is due to scratching fissure - a linear split in the Epidermis, often just extending into the Dermis folliculitis - an inflammation of the hair follicles furuncle - a pyogenic infection localised in a hair follicle keloid - an elevated and progressive scar not showing regression lichenification - chronic thickening of skin with increased skin markings, result of rubbing/scratching petechia - a haemorrhagic punctate spot measuring 1-2 mm in diameter purpura - extravasation of blood resulting in red discolouration of the skin or mucous membranes telangiectasia - dilated dermal blood vessels giving rise to a visible lesion Immunology of Skin Structures Epidermal barrier - innate immunity, protective barrier Cells Langerhans cell Outermost immune cell Important role in antigen presentation T lymphocyte Circulate through normal skin Different types are present Mast cell Normal residents of the Dermis Part of the inflammatory reaction Keratinocyte Have an immunological function Can produce pro-inflammatory Citokines Can express immune reactive molecules & intercellular adhesion molecules Functional Systems Skin-associated Lymphoid Tissue Skin has a regulatory immunological function Blood, Lymphatic drainage, circulating Lymphocytes & resident immune cells Cytokines & eicosanoids Mediate inflammatory response as well as action between cells Complement Activation of a complement cascade of events in the inflammatory response eg. Lysis & Chemotaxis for Neutrophils & Macrophages Adhesion molecules Help bind T cells & increase cell trafficking to the area Immunogenetics Tissue type Antigens of an individual These Antigens are found in the major histocompatibility complex (MRC) MRC located on the HLA gene cluster on chromosome 6 Vital for immunological recognition eg. Psoriasis is associated with the B13 HLA Antigen Hypersensitivity reactions and the Skin Inappropriate or exaggerated response where tissue damage results 4 types Type I (immediate) Type II (antibody-dependent cytotoxicity) Type III (immune complex disease) Type IV (cell mediated or delayed)

Understanding the Skin structure