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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