concerned with the diagnosis & treatment of skin
disorders'
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? However, dermatologists do not confine themselves
purely to a study of intrinsic disorders of the skin
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? Must also study internal medicine & the manyenvironmental & occupational factors that so
frequently cause skin problems
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Dermatology? Probably at least 2000 different skin conditions might
present to the dermatologist; vary enormously in
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severity
? Range from cosmetic problems, e.g., dry skin or
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wrinkles, through a huge variety of acute or chronicdiseases - disfiguring, itchy or painful, less commonly
fatal to life-threatening conditions
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? Certain diseases, if untreated, may prove fatal within
days (e.g., toxic epidermal necrolysis), weeks (e.g.,
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pemphigus), months (e.g., malignant melanoma) oryears (e.g., mycosis fungoides)
Dermatology
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? The patterns of dermatological diseases / disorders
vary from one country to another
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? Even in the same city the work of dermatologistsdiffer, depending on their particular interests &
expertise & on the social mix of their patients
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Dermatology? Largest organ of the body
? In a 70 - kg person: skin wt- >5 kg; SA = 2 m2
? Consists of a stratified, cellular epidermis & an
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underlying dermis of connective tissue
? Epidermis is mainly composed of keratinocytes & is
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typically 0.05 ? 0.1 mm in thickness, up to 1.5 mm inpalms & soles
Layers of Skin
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? Epidermis: Stratum basale (germinativum)
Stratum spinosum
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Stratum granulosum
Stratum lucidum (palms, soles)
Stratum corneum
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(Malphigian layer = basal + spinous layers)
? Dermis: Papillary dermis
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Reticular dermis
? Subcutaneous Fat
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m
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HPE Skin - forearm ? very thin epidermisHPE ? Palm ? stratum lucidum
Different Types of Cells in Epidermis
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? Keratinocyte? Melanocyte
? Langerhans' cell
? Merkel cell
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Strata (layers) of Epidermis? Stratum basale: Columnar / cuboidal cells; large
oval nuclei, dense basophilic cytoplasm
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? Stratum spinosum (spinous / prickle cell layer):
Polygonal cells with delicate processes,
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desmosomes connect adjacent keratinocytes? Stratum granulosum: Flattened diamond-
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shaped cells filled with coarse basophilic`keratohyaline' granules
Strata of Epidermis
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? Stratum lucidum : Clear layer found in palmsand soles, cells are nucleated, sometimes k/a
transitional cells
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? Stratum corneum : Flat, non-nucleated,
eosinophilic layer; cells k/a corneocytes
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Dead layer shed during epidermal turnoverEpidermal turnover/ transit time:
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? Time taken for a cell to pass from basal layer to
surface of skin
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? Apprx. 40 ? 56 days (normal skin)Melanocyte
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? Neural crest derived cells? Dendritic arborizing cells that synthesize and
secrete melanin containing organelles called
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melanosomes? Located in basal layer; 1:10 ratio
? Epidermal-Melanin Unit: A single melanocyte
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supplies melanosomes to 36 keratinocytes (1:36)? Melanosomes vary in number and size according
to skin type differing skin color
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Melanocytes in culture
Melanocyte
? Function of melanin
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- Impart colour to skin and hair
- Protect the skin from UV radiation
- Biochemical neutralizer of toxic, free radical
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oxygen derivatives
? Melanin: Eumelanin (brown / black) &
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phaeomelanin (yellow / red)Langerhans' cell & Merkel cell
? Langerhans' cell
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- Type of macrophage, APCs- Originate from bone marrow (mesodermal in
origin)
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- Role in various immune processes like allergiccontact dermatitis, immune tolerance,
surveillance against neoplasia
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? Merkel cell also k/a Merkel-Ranvier cell:
- Oval receptor cells
- Probably derived from keratinocytes
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- Associated with sensation of light touchdiscrimination of shapes & textures
Dermis
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? Papillary dermis ? A thin zone which lies beneaththe epidermis
? Reticular dermis - thick zone which extends from
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base of papillary dermis to the surface of
subcutaneous fat
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Structure of dermis? Mainly non-cellular connective tissue
? Constituted of collagen, elastic fibers & ground
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substance (mucopolysaccharides, chondroitinsulphate & glycoproteins)
? Embedded nerves, blood vessels / capillaries,
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lymphatics, muscles & pilosebaceous, apocrine
& eccrine units
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? Cellular contents include fibroblasts, mast cells,histiocytes, Langerhans' cells, lymphocytes &
eosinophils
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Variation in thickness of skin? Difference of thickness of the skin is dependent
largely on dermal thickness, with the palms and
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soles being thickest (about 1.5 mm) & thinnest
in the eyelids & post-auricular region (about
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0.05 mm)? Children & elderly have thinner skin than adults
? Males have thicker skin than females
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Hair? Hair - a keratinized product of the hair follicle, a tube
-like structure continuous with the epidermis at its
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upper end
? Present all over the skin except on vermillion of lips,
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palms, soles & skin of nail foldsTypes of hair
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Types of hair:1) Lanugo (fine, soft, unpigmented; seen in utero- shed
in 8th-9th month of gestation)
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2) Vellus (soft)3) Terminal (longer, coarse, pigmented)
Also intermediate
After puberty : secondary sexual terminal hair
Hair Cycle
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Hair follicles undergo a repetitive sequence of growth
& rest called the hair cycle
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Period of active hair growth is Anagen. Duration ofthis phase decides the length of hair; In humans, it is
maximum on scalp
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Catagen is the regressive phase in which the follicular
activity declines & ceases
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The hair stays in the Telogen (resting) phase till thebeginning of next anagen phase
Sebaceous Glands
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? Lipid producing holocrine glands
? Arise from the hair follicle at the junction of the
infundibulum & the isthmus
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? Distributed al over the body except the palms & soles;
most numerous, large and productive over the face &
scalp
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? Mature at puberty are stimulated by various hormones
? Major components of sebum: Triglycerides, wax
esters, squalene, cholesterol esters & cholesterol
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Nail
Nail Growth
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Functions of nailsHelp to grasp & manipulate objects
Help in `pincer grip'
Protect terminal phalanx & fingertip
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Serve an aesthetic & cosmetic purposeFunctions of Skin
? Barrier function
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? Permeability? Maintenance of fluid & electrolyte balance
? Thermoregulation- sweating
? Pigmentation
? Immune function
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? Sensory receptor? Endocrine function: Vitamin D synthesis
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