Fundamentals of Dermatology

Anatomy of the Skin – the Largest Organ in the Body (15% of body weight)

Regional Variations in Gross Anatomy

thickness – skin is thickest on back and soles of feet; thinnest on dorsum of hand and eyelid

hair – follicles are present everywhere except palms, soles, glans penis, labia minora, and clitoris

vellus hair (thin, on skin) vs. terminal hair (thick, on scalp)

glands (mostly in epidermis but can extend into dermis and subcutis):

eccrine (sweat) glands – absent only on glans penis and labia minora; most abundant on palms and soles

sebaceous (oil) glands – absent only on palms and soles

apocrine (scent) glands – present in axilla, anogenital region

dermal ridging – fingerprints – present only on palms and soles

Three Histological Layers

(1) epidermis – basal cell layer, stratum spinosum, stratum granulosum (granular), stratum lucidum (mainly on skin of palms and soles), stratum corneum (dead outermost layer)

consists of keratinocytes (produce keratin) and epidermal appendages (glands, hair and nails)

(2) dermis – made up of connective tissue (collagen, elastin, ground substance), blood, lymphatics, nerves, fibroblasts, immune cells (mast cells, macrophages); connected to epidermis by dermal-epidermal jct. (basement membrane)

(3) subcutaneous fat – below dermis; contains fat in addition to components found in the dermis

Functions of Skin

barrier – to water/electrolyte loss, germs, heat/cold, UV (damage to basal cell layer), exogenous chemicals

regulation of body temperature and blood pressure

secretion and excretion - sweat, sebum, urea, electrolytes

sensory organ - pain, itch, temperature, touch

Vit D production - action UV light on cutaneous 7-dehydroxycholesterol

color determination - via melanin, blood vessels

reservoir - for water, electrolytes, fat and protein

Terminology of Skin Lesions

Etiology – primary (associated directly with underlying process) or secondary (incidental lesions; ie picking at acne)

Flat (flush with regular skin) – macule (<1 cm; eg freckle) or patch (>1 cm; eg large port-wine stain)

Elevated (solid; raised above regular skin) – papule (<5 mm) or plaque (>5 mm or confluent collection of papules)

nodule/tumor – rounded mass elevated or below skin – includes subcutaneous nodules, eg cysts

wheal – solid, flat-topped, usually pale red, edematous, "hives" – e.g., solar erdekaria

Fluid Filled – vesicle (<1 cm; eg herpes, poison ivy) or bullae (>1 cm; tense v flacid)

pustule – filled with pus (acne)

Tissue Loss – erosion (loss of epidermis only, usually crusted) or ulceration (loss of dermis also or deeper)

Bruises – petechiae (<5 mm) or ecchymosis (>5 mm) – RBC’s in skin so do not blanche

telangiectasia tortuous blood vessels, so do blanche
blanching means discoloration when pressed

Atrophy – loss of skin thickness of epidermis, dermis or both – often by not always hypopigmentated

burrow - linear track produced by mites; comedone - blackhead or whitehead

Description of Rashes

Annular – ring shaped, edge raised due to central clearing, e.g., ringworm fungus

Nummular – coin shaped, no central clearing, e.g., eczema

Targetoid – like a target; concentrically darker rings, also called iris lesion – often from infection or drug

Verrucous – wart-like, Acneiform – acne-like, Eczematoid – eczema-like (thickened skin with scale, vesiculate, crusted)

Guttate – paint-drop like – as if paint droplets splattered all over patient body

Serpiginous – snake-like, winding, curvy

Zosteriform – along one nerve, does not cross midline of body – e.g., shingles (reactivated chicken pox, herpes zoster)

Other Shapes: arcuate (arc), cirinate (circle), discoid (disc), linear (line), moniliform (beaded)

Can be discrete, confluent, or universal (entire skin)

Multiform or polymorphous – more than one type of lesion

Other Terms

Spindle cell layer – acantholysis (separation of spindle cells), acanthosis (thickening), spongiosis (edema between cells)

Sweating: anhidrosis (absence) or hyperhidrosis (excess)

Hair: alopecia (absence) or hirsute (excess)

Color: erythema (red), purpura (bruised), hemmorrhagic (bleeding into skin)

Nail bed: onycholysis (separation from overlying nail plate), pitting (punctate depressions)

Dystrophy - maldevelopment; Granulamotous - chronic inflammatory process; keratosis -circumscribed horny thickening