Anatomy and histology of the skin. Skin – the more large organ in the body surface – 1.5-1.8 sqm; thickness: 0.2-0.5 mm (eyelid, prepuce); 3-5
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Anatomy and histology of the skin
Skin the more large organ in the bodysurface 1.5-1.8 sqm;thickness: 0.2-0.5 mm (eyelid, prepuce);3-5 mm (palms and soles).weight:4-5 kg;20 kg with hypodermis.glabrous skin palms and soles;hair bearing skin.
Organization of the human skin:the skin is composed of four distinct layers:the epidermis;the dermo-epidermal junction;the dermis;the hypodermis.
Histology of the epidermisstratum germinativum (Basal cell layer);stratum spinosum (Squamous cell layer); viable epidermis;stratum granulosum (Granular cell layer);stratum lucidum;stratum corneum (Horny layer) nonviable epidermis.KeratinocytesDendritic cells
Basal Cell Layera single range of columnar cells, with basophilic cytoplasm, dark-staining oval or elongated nucleus, many ribosomes, tonofibrils (keratin filaments) into fine bundles, melanin granules (transferred from melanocytes);
the cells are connected with each other by desmosomes (symmetrical, laminated structures) and with basement membrane by hemidesmosomes.
Basal cell layer (glutaraldehide- osmium fixation)
Squamous Cell Layer5-20 ranges of polygonal cells with long axis parallel to the skin surface, eosinophilic cytoplasm, clear rounded nucleus, large bundles of keratin filaments, attached to desmosomes;
the new organelles in the upper spinous cells lamellar granules (keratinosomes, Odland bodies) they contain polysaccharides, free sterols, lipids, hydrolytic enzymes; their contents are discharged into the intercellular space at interface with granular layer.
Squamous cell layer
Granular Cell Layer3-10 ranges of diamond-shaped or flattened cells, with horizontal long axis, cytoplasm filled with basophilic kertohyaline granules (irregular in size and shape, with particulate substructure);
the dissolution of the nucleus and cell organelles is initiated; keratin filaments in large bundles;
keratinosomes migrate towards the periphery of the cells and discharge their lipid components.
Horny Layer4-10 ranges of eosinophilic, flattened cells, arranged in vertical stacks, that have lost nuclei and cytoplasmic organelles;
keratin filaments are aggregated in macrofibres under the influence of filaggrin;
highly insoluble cornified envelope within the plasma membrane, that contain involucrin, loricrin, keratolinin;
the loss of desmosomes.
Stratum luciduman additional homogenous eosinophilic zone between granullar cell layer and horny layer, in palmo-plantar skin;
contains cells with dense cytoplasm, opaque membranes, degenerated nucleus, without organelles;
keratin filaments are immersed in a matrix of eleidine.
Acral skin layers of the epidermis: basal (green), squamous (black), granulous (red), lucidum (blue), horny (yellow). Blood vessels (arrows from dermis).
EpidermisMelanocyteDermisMelanin granulesLangerhans CellsKeratinocyte
Dendritic Cells of the Epidermis - Melanocytesdendritic cells localized between the basal cells;in section stained with hematoxylin-eosin-clear cells, with small, dark-staining nucleus, clear cytoplasm;the dendritic processes recognized with dopa reaction, staining with silver nitrate;in electron microscopy differ from keratinocytes by lack of tonofilaments or desmosomes;melanocytes contain melanosomes, specialized organelles that synthesize melanin, that is transferred to keratinocytes (apocopation);the evolution of melanosomes in 4 stages: round, ellipsoid, partially melanized, completely melanized.
Langerhans Cellsdendritic cells of mesenchimal origin, localized in suprabasal epidermis, dopa negative;
in sections stained with hematoxylin-eosin-clear cells;
histochemical stains (adenosine phosphatase, aminopeptidase) for identifying and differentiating from melanocytes alfa D manositase; staining with gold chloride;
demonstrated with monoclonal antibody OKT6; by immunoperoxidase technique or immunofluorescence;
Langerhans Cellsin electron microscopy relatively clear cytoplasm, lobulated nucleus, well developed endoplasmic reticulum, Golgi complex and lysososmes; lack of tonofilaments and desmosomes, presence of Bierbeck granules; recognized by monoclonal antibody anti-Lag (Langerhans-associated granule);
Langerhans cells express on their surface HLA-DR, DP and DQ antigens, T6 antigen CD1 (CD1a, CD1c), CD4 (HIV receptor), CD14, CD33, VLA (very late antigen), adhesion molecules et al. and have receptors for Fc (Fc and Fc) of IgG and IgE and C3b, C4d, CD23 (IgE receptor in atopic dermatitis), DEC 205 multilectine etc. A new identified lectine (Langerin) is a endocitic receptor.
Merkel Cellsdendritic cells localised between the basal cells, directly above the basement membrane;in light microscopy can be recognized in silver impregnated sections;in electron microscopy lobulated nucleus, clear cytoplasm, electron-dense granules, strands of filaments, occasional desmosomes; unmyelinated nerve endings are associated with Merkel cells.
Indeterminate Cellshave ultrastructural features of Langerhans cells but lack Birbeck granule;
react specifically with the monoclonal antibody OKT6.
Histology of the dermo-epidermal junctionthe indeterminate filaments of basal keratinocytes;
the basal plasma membrane of keratinocytes, melanocytes and Merkel cells;
hemidesmosomes: focal thickenings of the basal plasma membrane of keratinocytes, with an intercellular component (the attachement plaque) and an extracellular component (sub-basal dense plate);
the basement membrane with 3 layers: lamina lucida, lamina densa and lamina fibroreticularis;
anchoring filaments: very fine, vertically orientated structures that connect hemidesmosomes at lamina densa;
anchoring fibrils: short curved structures that insert into the lamina densa and extend into the dermis and insert into anchoring plaques or curve back in lamina densa;
anchoring plaques: amorphous bodies in the superficial dermis;
the elastic microfibrils, that extends into the dermis and may enmesh with dermal elastic fibres.
Histology of the dermisLayers of the dermis:papillary dermis (the uppermost part);reticular dermis (subpapillary layer).
Components of the dermis:cells;fibres;ground substance.
Cells of the dermis:fibroblast - a cell at an early stage of differentiation;fibrocyte a cell fully differentiated;mesenchymal origin;small and spindle shaped (S-cell) or larger, flatter, amoeboid (A-cell);produce collagen and elastine.
Cells of the dermis:mast cell: originate from haematopoietic bone marrowovoid or spindle shape, mono or binuclear, with round acidophilic cytoplasmic granules, which stain metachromatically with toluidine blue or Giemsa;
localized around blood vessels, nerves and appendages, in subpapillary dermis;
Cells of the dermis:macrophage: originate from bone marrow, is larger than monocyte, with clear cytoplasm, lighty staining elongated nucleus, well developed rough endoplasmic reticulum and Golgi apparatus, intermediate filaments;is a general scavenger implicated in the ingestion and killing of micro-organisms and the degradation of foreign substances;secrete several enzymes;possess numerous receptors.
Fibers of the dermis:collagen fibers:in light microscopy: bands with faint longitudinal striations; in dark field, each fiber is a bundle of parallel fibrils;in E.M.: fibrils with cross striations;structure of collagen: 3 polypeptide chains, coiled in a triple helix (helical domain) and a globular domain at each end (amino-N-terminal domain and carboxy-terminal domain).
reticulin fibers:a special type of thin collagen fibers;in light microscopy, with silver nitrate stains black;in E.M.: fibrils separated by an interfibrilar substance.
Fibers of the dermis:elastic fibers:in light microscopy, with orcein or resorcin-fuchsin, thin bundles, that in the papillary dermis form an intermediate plexus of elaunin fibers running parallel to the dermal-epidermal junction; oxytalan fibers, perpendicular to the dermal-epidermal junction;
Ground substancean amorphous substance: contains proteoglycans, glycosaminoglycans, electrolytes, water;the staining methods of the ground substance:the production of metachromasia;colloidal iron;Alcian blue, ruthenium red;
in electron microscopy: flocculent and filamentous material.
Histology of the hypodermisadipocytes, organized into lobules defined by septa of fibrous connective tissue with blood vessels and nerves.
Skin and its appendages
Histology of the skin appendagesEccrine sweat gland2-4 million, distributed over nearly entire body surface; most numerous on the palms, soles and in the axillae;two segments:the secretory coil; the duct.the secretory coil: 3 cell types:clear (secretory) pyramidal, with abundent mitochondria, a lipofuscin cell granule;dark (mucoid) cuboidal or pyramidal, with dark granules;myoepithelial cells;the duct:in the dermis: 2 layers: basal cells (outer ring), luminal cells (inner ring); membrane;in the epidermis: 1 layer luminal cells;opens directly onto the skin surface.
Eccrine sweat gland
Histology of the skin appendagesApocrine sweat glandlimited to the axillae, nipples, perineum and genitalia, groin, periumbilical area;larger than eccrine gland;opens in the folliculary duct.
Apoeccrine sweat gland50% of axillary glands in the adults with axillary hyperhydrosis;a long duct which opens directly into skin surface.