Histology of Skindr. Alya Amila Fitrie, M.Kes dr. Radita Nur AnggraeniDepartment of HistologyMedical Faculty University of North Sumatera2012

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INTRODUCTIONThe heaviest single organ of the body, 16% of TBW.Presenting 1,2 2,3 m2 of surface.Composed of :Epidermis : an epithelial layer of ectodermal originDermis : a layer of connective tissue of mesodermal origin.*

Comparative thickness of the skin*

EPIDERMISConsist mainly of a stratified squamous keratinized epithelium keratinocytes.Three

Five layers of keratin-producing cells (keratinocytes) :Stratum basale (stratum germinativum)Stratum spinosumStratum granulosumStratum lucidumStratum corneum*

Stratum basale (Stratum germinativum)Single layer of basophilic columnar or cuboidal cell resting on basement membrane at the dermal-epidermal junction.Desmosom (+), hemidesmosom (+)Stem cells intense mitotic activity & is responsible, in conjunction with the initial portion of the next layer, for constant renewal of epidermal cells.Human epidermis is renewed about every 15-30 days. *

Stratum spinosumConsists of cuboidal or slighly flattened cell, a central nucleus, a cytoplasms processes : bundles of keratin filaments, a spine-studded appearance (tonofilaments).The filaments : Maintaining cohesion among cellsResisting the effect of abrasionStratum basale + stratum spinosum = stratum Malpighi mitoses

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Stratum spinosum (cont.)*Stratum spinosum of the thick skin from sole of the foot. Pararosaniline-toluidine blue. Medium magnification

Stratum granulosumConsists of 3-5 layers of flattened polygonal cells, cytoplasm filled with keratohyalin granules.The membrane-coated lamellar granules : containing lamellar disks that are formed by lipid bilayers. This granules : fuse with cell membrane discharge their contents intercellular spaces of stratum granulosum form of sheets containing lipid*

Stratum lusidumTranslucent, thin layer of flattened eosinophilic epidermal cells.Organelles & nuclei (-)Cytoplasm : densely packed keratin filamentsDesmosom (+) between adjacent cells*

Stratum corneumConsists of 15-20 layers of flattened nonnuclea-ted keratinized cells.Cytoplasm : a birefringent filamentous scleroprotein, keratin.After keratinization, the cells consist of only fibrillar & amorphous proteins; & thickened plasma membrane horny cells or corneocyte*Cornified envelope lipids

MelanocytesA specialized cell of the epidermis found beneath or between the cells of the stratum basale & in the hair follicles.Derived from neural crest cells.

*Hemidesmosomes(+), desmosome (-)

MelanogenesisTyrosinase is synthesized in the RER, accumulated in GoC vesikel : melanosom. Melanin synthesis in the melanosom II melanosom III melanin granules. Melanin granules migrates & transferred to the keratinocytes of the malpighian layer.*http://www.ambion.com/tools/pathway/loadImage.php?pos=bl&im=images/Melanocyte%20Development%20and%20Pigmentation.jpg

MelanocyteMelanin granules accumulate in the supranuclear region of the cytoplasm protecting from deleterious effects of solar radiation.*

Langerhans CellsStar-shapedLocation : stratum spinosumBone marrow-derivedImportant in immunologic skin reaction*

Merkels CellsGenerally in the thick skin of palms and soles.Resemble the epidermalepithelial cells, with small dense granules in cytoplasm.Free nerve ending at the base.*

Immunologic Activity in the SkinIts large sizeLymphocytes >>>Antigen-presenting cells (APC)Close contacts with antigenic molecules

Epidermis has an important role in some types of immune response*

DERMISDermis is connective tissue that Support epidermisBinds epidermis to hypodermisThe thickness : variesThe surface : irregular dermal papillae >< epidermal ridges.Contains 2 layers :Papillary layerReticular layer

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Papillary LayerComposed of :Loose connective tissueFibroblastsOther connective tissue cells : mast cells & macrophagesExtravasated leukocytesAnchoring fibrils (+) : special collagen fibrils*

Reticular LayerComposed of : Irregular dense connective tissue (type I collagen)More fibers, fewer cells.Contains a network of fibers of elastic system responsible for the elasticity of the skin.

*Thick section of skin stained for the fibers of the elastic fibers. Weigerts stain

DERMIS (cont)Rich network of blood & lymph vessels.Arteriovenous shunt temperature regulation.In addition, dermis contains : epidermal derivatives :Hair follicleSweat & sebaceous glandsNerves*

Subcutaneous TissueConsists of loose connective tissue.Contain fat cells that vary in number & size.Referred to superficial fascia , >> panniculus adiposus*

Skin & Lymphatic VesselsThe arterial vessels 2 plexuses :between papillary reticular layerbetween dermis subcutaneous tissueThe venous 3 plexuses :Like arterial vessels + in the middle of the dermis.Lymphatic vessels : begin as closed sacs in the papillae of dermis form two plexuses.

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Skin Sensorial ReceptorsFree nerve endings The expanded : Ruffini endings The encapsulated : Vater-PaciniMeissnerKrause.*

Meissner & Paccinian corpuscle*

GLANDS OF THE SKINSweat glandsEccrineApocrineSebaceous glandsMammary gland*

Sweat GlandEcrine (merocrine) sweat glandSimple coiled tubular glandThroughout skin important in regulation of body temperatureSecretory unit dark cells & clear cellsApocrine sweat glandFound only in axilla, areola nipple, anal region Modified apocrine sweat glands ceruminous glands of ear, glands of moll in eyelidsLarger than eccrine, lumen of secretory tubulus is larger

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Sweat Gland*

Sebaceous GlandSecrete sebum oily substanceEmpty secretory product into the upper parts of the hair follicles Not found in palms of hand, soles of feet, sides of feet inferior of hairlineClinically the sebaceous glands are important in that they are liable to infections (e.g. with the development of acne)

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Sebaceous Gland*

HAIRSElongated keratinized structure Develop from epidermis & invade the dermis & hypodermis Everywhere except palms, sole, glans penis, clitoris & labia minoraHairs grow discontinously have periods of growth (anagen) followed by period of rest (telogen)In scalp : growth period several years, rest period 3 monthsHair in scalp, face & pubis strongly influenced by androgens, adrenal & thyroid hormones

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Hair follicle*

NAILSHighly keratinized epithelial cells arranged in plates of hard keratin Develop from nail matrix nail root Stratum corneum forms eponychium or cuticle nail plateNail plate on nail bed

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Histology of Nail

E=eponychium, H= hyponychium, N=nail plate, DP=distal phalanx*

ReferencesJunqueira, L.C. & Carneiro, J. Basic Histology, Text & Atlas, 11th edition, Lange Medical Books McGraw-Hill. 2005Gartner, L.P. & Hiatt, J.L. Colour Textbook of Histology, Third Edition. 2007Kierszenbaum AL. Histology & Cell Biology, An Introduction to Pathology, 2nd ed. Mosby Elsevier. 2007

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