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anatomy of skin
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Anatomy of Skin and Basic Skin Lesions
Layers of SkinEpidermis - stratum basale - stratum spinosum - stratum granulosum - stratum corneumDermis - papillary dermis - reticular dermis Subcutaneous Fat
Types of Cells in EpidermisKeratinocyteMelanocyteLangerhans cellMerkel cell
Strata of EpidermisStratum basale: Cuboidal / columnar cells; large oval nuclei, dense basophilic cytoplasm
Stratum spinosum (spinous/prickle cell layer): Polygonal cells with delicate processes, desmosomes connect adjacent keratinocytes Stratum granulosum: Flattened diamond shaped cells filled with coarse basophilic keratohyaline granules
Strata of EpidermisStratum lucidum : Clear layer found in palms and soles
Stratum corneum : Flat, anuclear, eosinophilic corneocytes Dead layer shed during epidermal turnover
Epidermal turnover/ transit time: Time taken for a cell to pass from basal layer to surface of skin. 52-75 days (normal skin)
MelanocyteNeural crest derived cellsDendritic cells that synthesize and secrete melanin containing organelles called melanosomesLocated in basal layer; 1:10 ratioEpidermal Melanin Unit: A single melanocyte supplies melanosomes to 36 keratinocytes(1:36)
Melanosomes vary in number and size according to skin type
MelanocyteMelanin formed through mediation of tyrosinase and DOPAFunction of melanin - Impart colour to skin and hair- Protect the skin from UV radiation - Biochemical neutralizer of toxic, free radical oxygen derivatives
Langerhans cell and Merkel cellLangerhans cell- Type of macrophage- Role in various immune processes like allergic contact dermatitis, immune tolerance, surveillance against neoplasia
Merkel cell- Neuritic cells - Touch receptors- Detect mechanical deformities of epidermis
Functions of EpidermisCornificationBarrier functionPermeabilityMaintenance of fluid and electrolyte balanceThermoregulationPigmentationImmune functionSensory receptorVitamin D Synthesis
DermisPapillary dermis - thin zone beneath epidermis
Reticular dermis - thick zone which extends from base of papillary dermis to the surface of subcutaneous fat
Structure of dermisNon-cellular connective tissueConstituted of collagen, elastic fibers and ground substance (mucopolysaccharides, chondroitin sulphate, glycoproteins)Embedded nerves, blood vessels, lymph vessels, muscles and pilo sebaceous, apocrine and eccrine unitsCellular contents include fibroblasts, mast cells, histiocytes, Langerhans cells, lymphocytes and eosinophils
Variation of thickness of skinDifference of thickness of the skin is dependent largely on dermal thickness, with the palms and soles being thickest (1.5 mm) and thinnest in the eyelids and post-auricular region (0.05 mm).Children and elderly have thinner skin than adultsMales have thicker skin than females
Dermo-Epidermal JunctionConsists of - Basal lamina - Lamina lucida - Lamina densa - Anchoring filaments - Anchoring fibrils - Dermal microfibril bundles
Functions of Dermo-Epidermal junctionAttachment of dermis to epidermisSupport to epidermisRegulation of permeabilityAutoantibodies to proteins in the dermo-epidermal junction may be responsible for vesiculobullous disorders
Embryology of skin All constituents derived from ectoderm and mesoderm
Ectoderm and mesoderm begin to proliferate and differentiate at 4th week of intrauterine life
The specialised structures of skin, teeth, hair, nails and glands begin to appear at this time
Epidermal AppendagesHair folliclesSebaceous glands Apocrine glandsEccrine glands
HairTypes - Lanugo - Vellus - Terminal
Sites of hair folliclesFound over the entire surface of the body except palms, soles, glans penis, clitoris, labia minora, mucocutaneous junction and distal portions of the fingers and toes
Anatomy of hairLongitudinal section Infundibulum Isthmus Stem BulbCross sectionOuter sheathInner sheath - Henles layer - Huxleys layer - CuticleCortex Medulla
Phases of hair growthHair cycle consists of three phases:Anagen : Growing phase lasts for 2-10 years. About 90% of hair are in anagen at a time.Catagen : Involution phase lasts for 1-3 weeks. About 1% hair are in catagen.Telogen : Resting phase lasts for about three months. About 10% hair are in telogen.Telogen hair is shed and anagen hair replaces it.
Sebaceous GlandsLipid producing holocrine glandsArise from the hair follicle at the junction of the infundibulum and the isthmusDistributed all over the body except the palms and soles; most numerous , large and productive over the face and scalpMature at puberty and are stimulated by various hormones
Sebaceous GlandsConsists of lobules of epithelial cells that differentiate toward lipid producing cells in a centripetal mannerEnlarged, vacuolated cells in the center of the lobule disintegrate into an amorphous mass - sebumMajor components of sebum: Triglycerides, wax esters, squalene, cholesterol esters and cholesterol
Eccrine Sweat glandsThermoregulationEntire surface of the body except the lips, external ear canal and labia minoraMost concentrated in the palms and soles
Apocrine Sweat GlandsVestigial sexual functionAxillae and anogenital regionsMammary glands considered modified and specialized type of apocrine glands
Blood / Lymphatic supply of skinExtensive subdermal and dermal plexusesDermal plexus: Horizontal superficial and deep plexuses, connected by vertical communicating vesselsCutaneous vasculature important in thermoregulation Cutaneous lymphatics parallels the blood supply
Skin innervation Light touch: Merkel cells of the epidermis, Meissners corpuscles in dermal papillaePressure: Pacinian corpuscles in deep dermis or subcutaneous tissuePain: transmitted through naked nerve endings located in the basal layer of the epidermisTemperature: - Krause bulbs detect cold, Ruffini end organs detect heat - Heat, cold and proprioception also located in the superficial dermis - Adjacent dermatomes often overlap, important in local anaesthesia
ClassificationPrimary lesionsSecondary lesionsSpecial lesions
Basic Skin Lesions
Primary Skin LesionsMaculePatchPapulePlaqueNoduleWhealVesicleBullaPustuleCyst
Secondary Skin LesionsScaleCrustExcoriationFissureErosion
Ulcer ScarLichenification Induration Atrophy
Special Skin Lesions BurrowComedoMilium Poikiloderma Telangiectasia Target lesion
MaculeDefinition: A circumscribed alteration in the colour or texture of the skinTypes: Erythematous, hypopigmented, hyperpigmented, depigmented, purpuricExamples: caf au lait macule, vitiligo
Erythema / PurpuraErythema: Redness of the skin, blanches on pressure and is due to vascular congestion or increased perfusion. Eg: SLE, RosaceaPurpura: Discoloration of skin or mucous membrane, non- blanchable due to extravasation of red blood cells. Eg: Vasculitis, clotting disorders Petechiae: 1-2 mm small purpuric lesions, occurs in crops. Eg : clotting disordersEcchymoses: larger extravastions of blood. Eg: post traumatic
Papule Definition: A circumscribed palpable elevation, less than 1 cm in diameter
Types: dome-shaped, flat-topped, umbilicated, pedunculated
Examples: Warts, Molluscum
Plaque Definition: An elevated area of skin, 1cm or more in diameter; surface area is greater than the height.
It may be formed by the extension or coalescence of either papules or nodules
Examples: psoriasis, granuloma annulare
NoduleDefinition: A solid mass in the skin, which can be observed as an elevation or can be palpated. It is more than 0.5 cm in diameter.
The depth of a nodule differentiates nodules from papules. The absolute size is probably not very important.
Examples: furuncle, erythema nodosum
Vesicles and BullaeDefinition: Visible accumulations of fluid within or beneath the epidermis. Vesicles are small, less than 0.5 cm in diameter. Bullae are larger and may be of any size above 0.5 cm in diameter.
Examples: Herpes simplex, Eczema, Pemphigus, Burns, Impetigo
PustuleDefinition: A visible accumulation of free pus. It may occur in association with infection or may be sterile
Examples: Bacterial / Candidial infections, Psoriasis (sterile)
Wheal Definition: An area of dermal or dermal and hypodermal oedema, erythema and pallor; which is evanescent
Examples: characteristic lesion of urticaria
Cyst Definition: Any closed cavity or sac (normal or abnormal) with an epithelial, endothelial or membranous lining and containing fluid or semisolid material
Examples: epidermal cysts, pilar cysts, sebaceous cysts
ScaleDefinition: Visible exfoliation of a flat plate or flake of stratum corneum
Examples:Furfuraceous - Pityriasis VersicolorIchthyotic, lamellar- IchthyosisMicaceous - PsoriasisCollarette - Pityriasis rosea
CrustDefinition: Crusts consists of dried serum and other exudates
Types: hemorrhagic crust (scab), purulent
Examples: Impetigo
ExcoriationDefinition: Loss of skin substance produced by scratching
Types: - linear - circumscribed
Examples: Acne excoree, Prurigo
FissureIt is a linear crack in the skin, which may be superficial or deep to the dermis
ErosionDefinition: A loss of whole part of epidermis, which heals without scarring. It commonly follows a blister
Examples: Impetigo Pemphigus
Ulcer Definition: A loss of epidermis and some parts of dermis, may involve underlying tissues.
Examples: trauma, stasis ulcer
ScarDefinition: A replacement by tissue that has been destroyed by injury or disease by fibrous tissue
Types: atrophic hypertrophic cribriform varioliform pitted
LichenificationDefinition: The thickening of the epidermis and to some extent of the dermis, pigmentation and accentuation of skin markings,in response to prolonged rubbing.
Examples: Lichen simplex chronicus
IndurationDefinition: firm and thick skin due to dermal involvement
SclerosisDefinition: A diffuse or circumscribed induration of the subcutaneous tissues. It may also involve the dermis.
Sclerosis is better felt than seen
Examples: Scleroderma
AtrophyDefinition: A loss of tissue characterized by the loss of normal skin markings
Types of atrophy: Epidermal, dermal, subcutaneous, mixed
Loss of skin markings occur in epidermal atrophy only
Burrow Definition: A small tunnel in the skin that houses a metazoal parasite
Examples: Scabies
ComedoDefinition: A plug of keratin and sebum in a dilated pilosebaceous orifice
Types: open closed
Examples: Acne
TelangiectasiaDefinition: visible and permanent dilatation of capillaries
Types: punctate, matt-like, linear, spider
Examples: Rosacea Nail fold telangiectasias in systemic sclerosis
MiliumDefinition: A tiny white cyst containing lamellated keratin
Milia are lined by epithelium
PoikilodermaDefinition: The association of cutaneous pigmentation, atrophy and telangiectasia
Examples: Dermatomyositis
Target lesionsDefinition: These are less than 3 cm diameter and have 3 zones; a central zone of dusky erythema or purpura, a middle paler zone of oedema and an outer ring of erythema with a well-defined edge.
The diameter of target lesions may not be significant
Examples: Erythema multiforme
AlopeciaDefinition: Loss of hair from a normally hairy area
Types: Scarring, Non-scarring
Examples: Alopecia areata, Androgenic alopecia
PatternsAnnularLinearGroupedDiscoidReticulate
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