Overview of the Skin

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Overview of the Skin

• The skin is one of the largest organs in the
  body
• surface area ? 1.8 m2
• weight approximately 16 of our body weight
• Four main functional areas
• 1. Epidermis the major protective layer
  derived from ectoderm  
• 2. Dermis the major support layer derived
  from mesoderm
• 3. Skin Appendages derived from both
  ectoderm and
• 
  mesoderm 
• Eccrine Sweat Gland    Apocrine Sweat
  Gland    Sebaceous Gland    Hair
  Follicle    Nails
• Arrector Pili muscle
• 4. Subcutis this layer consists of loose
  connective tissue and fat

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SKIN
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Functions of the Skin

1. barrier to physical agents
2. protects against mechanical injury
3. prevents dehydration of body through fluid loss
4. reduces the penetration of UV Radiation
5. helps regulate body temperature
6. acts as a sensory organ
7. acts as an outpost for immune surveillance
8. plays a role in Vitamin D production
9. has a cosmetic association 

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Epidermis
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Epidermis I.

• a continually renewing, stratified, squamous
  epithelium that keratinizes and gives rise to
  derivative structures (pilosebaceous units, nails
  sweat glands) called appendages
• about 0.4 to 1.5 mm in thickness (thickest ---
  palms soles)
• full-thickness skin1.5-4 mm

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Epidermis II.

• keratinocytes
• Melanocytes
• Langerhans cells
• Merkel cells
• basement membrane separates epidermis dermis,
  mediates their attachment
•  

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Keratinocyte

• ectodermally derived
• gt 80 percent of the epidermal cells
• cytoplasmic keratin filaments
• 1.gt30 different keratins
• 2.a hallmark of the keratinocyte and other
  epithelial cells
• 3.structural (cytoskeletal) role
• desmosomes
• modified desmosomal junctions

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Layers of the epidermis
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1.Basal Cell Layer (stratum basale) I

• Mitotically active, columnar-shaped
  keratinocytes. attach to the basement membrane
  zone by hemidesmosomes.
• The normal transit time for a basal cell,
• from the time it detaches from the basal
  layer to the
• time it enters the stratum corneum, is at
  least 14
• days.
• Transit through the stratum corneum and
• desquamation require another 14 days.

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1. Basal Cell Layer (stratum basale) II

• Melanocytes 5-10 of the layer and make melanin
  which is transferred to neighboring keratinocytes
  via dendritic processes
• neural crest origin
• most numerous on the face and other exposed areas
  of skin
• Epidermal melanin unit Approximately 36 basal
  and suprabasal keratinocytes are thought to
  coexist functionally with each melanocyte
• Merkel cells among basal keratinocytes in
  particular regions of the body (in hairy skin and
  in the glabrous skin of the digits, lips, regions
  of the oral cavity, and the outer root sheath of
  the hair follicle) and join with them by
  desmosomal junctions
• mechanoreceptors

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2. Spinous Cell Layer (stratum spinosum)

• Suprabasal spinous cells are polyhedral in shape
  (spine-like appearance of the cell margins)
• The spines of spinous cellsabundant
  desmosomes, calcium-dependent cell surface
  modifications that promote adhesion of epidermal
  cells and resistance to mechanical stresses
• Desmosomesa mechanical coupling between
  epidermal cells, gap junctions between
  keratinocytes are sites of physiologic
  communication (regulation of cell metabolism,
  growth, and differentiation)
• Langerhans cells from bone marrow, mostly found
  in this layer. dendritic, immunologically active
  cells that play a role in antigen presentation. 

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3. Granular Cell Layer (stratum granulosum)

• Flattened cells and lose their nuclei. In
  cytoplasm, keratohyalin granules as well as
  membrane-coating granules which expel their lipid
  contents into the intercellular spaces. 
• The most apparent structures within these cells
  basophilic, keratohyalin granules
• Keratohyalin granules are membrane-coating
  granules which expel their lipid contents into
  the intercellular spaces. 
• At the interface between the granular and
  cornified cell layers, barrier lipids (e.g.,
  sphingolipids) are formed

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4. Horny Layer (stratum corneum)

• Complete transition from a granular to a
  cornified cell is accompanied by a 45 to 86
  percent loss in dry weight
• The layers of resultant cornified cells provide
  mechanical protection to the skin and a barrier
  to water loss and permeation of soluble
  substances from the environment
• The stratum corneum barrier is formed by a
  two-compartment system of lipid-depleted
  protein-enriched corneocytes surrounded by a
  continuous extracellular lipid matrix
• Horny cell
• 1. the flattened, polyhedral-shaped, horny
  cell is the largest cell
• of the epidermis
• 2. Its shape and surface features are adapted
  to maintain the
• integrity of the stratum corneum yet
  allow for desquamation
• 3. the cell contain keratins and filaggrin
• Three key lipid typescholesterol, ceramides, and
  free fatty acidsform the lamellar bilayers

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Regulation of Epidermal Proliferation and
Differentiation

1. Integrins Keratinocytes express several
   integrins and important to skin homeostasis
2. Growth Factors epidermal growth factor (EGF),
   transforming growth factor (TGF)-a, TGF-ß,
   keratinocyte growth factor (KGF)...
3. Cytokines keratinocyte-derived cytokines
   (interleukin (IL)-1a, IL-6, IL-8) and
   granulocyte-macrophage colony-stimulating factor
   (GM-CSF)
4. Retinoids
5. Vitamin D3
6. Calcium
7. Apoptosis

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The dermalepidermal junction (DEJ)

• The DEJ is a basement membrane zone that forms
  the interface between the epidermis and dermis
• Function
• 1. attach the epidermis and dermis to each
  other
• 2. provide resistance against external
  shearing forces
• 3. serves as a support for the epidermis
• 4. determines the polarity of growth
• 5. directs the organization of the
  cytoskeleton in
• basal cells
• 6. provides developmental signals
• 7. serves as a semipenetrable barrier

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Three supramolecular networks of DEJ

• Hemidesmosome-anchoring filament complex
• 2. Basement membrane
• 3. Anchoring fibrils

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Overview of the Dermis

• a supportive connective tissue matrix containing
  numerous specialized structures.
• The dermal thickness varies being thinnest (0.6
  mm) on the eyelids and thickest (3 mm or more) on
  the back, palms, and soles.

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Contains of the dermis I

• 1. Collagen fibers
• Make up 70 of the dermis and give structural
  toughness and strength.
• Type I, III, and V account for the greatest
  proportion of the collagen in adult dermis
• 2. Elastic fibers
• Account for 4 of the dermal matrix protein
• loosely arranged in all directions and give
  elasticity to the skin
• Elastic fibers are also present in the walls of
  cutaneous blood vessels and lymphatics and in the
  sheaths of hair follicles

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Contains of the dermis II

• 3. Ground substance
• consists of a semi-solid matrix of Proteoglycans
  ( hyaluronic acid, chondroitin sulfate, heparan
  sulfate)
• 4. Cells
• Fibroblasts
• Macrophages
• Mast cells

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Organization of the Dermis

• 1. Papillary Dermis
• Beneath the epidermis extending to vascular
  boundary of subpapillary plexus
• 2. Rticular Dermis
• The dominant region of the dermis
• Composed of large-diameter collagen fibers and
  mature elastic fibers

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Cutaneous vasculature I

• Function
• provide nutrition
• regulation of temperature
• blood pressure
• wound repair
• immunologic events

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Cutaneous vasculature II

• 1. Arteries
• Musculocutaneous arteries in the subcutaneous fat
  migrate upwards to give rise to a subpapillary
  plexus at the papillary/reticular dermal
  boundary.
• Subpapillary plexus gives off branches of its own
  that branch upwards to the dermal papillae.
• Each dermal papillae has a single loop of
  capillary vessels, one arterial and one venous.

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Cutaneous vasculature III

• 2. Veins
• Veins drain from the venous side of the loop and
  branch downward to form the venous return network
  of the mid-dermis and subcutaneous layer.

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Cutaneous vasculature IV

• 3. Lymphatic Vessels
• Function regulating pressure of the interstitial
  fluid, clearing the tissue of cells, proteins,
  lipids, bacteria, and degraded substances
• The lymphatics originate in the papillae then
  drain into increasingly larger vessels that
  ultimately reach the regional lymph nodes.

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Nerves and Receptors I

• The nerve networks of the skin
• somatic sensory
• sympathetic autonomic fibers
• Nerve fibers of the skin
• myelinated or non-myelinated
• contain neuropeptides such as
• substance P.

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Nerves and Receptors II

• 1. Sensory fibers
• The sensory fibers are receptors of touch, pain,
  temperature, itch, and mechanical stimuli
• Rceptors are particularly dense in hairless areas
  such as the palms, face areola, labia, and
  glanspenis
• Free sensory nerve endings can be seen in both
  the dermis and the epidermisIn the epidermis,
  they may end on Merkel cells which detect pain,
  itch and temperature.
• In the dermis, there are specialized corpuscular
  receptors such as
• Pacinian corpuscle detects pressure and
  vibration
• Meissner's corpuscle touch sensitive and mainly
  located in the dermal papillae of the hands and
  feet.

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Nerves and Receptors III

• 2. Motor fibers
• Sympathetic motor fibers are codistributed with
  the sensory nerves in the dermis until they
  branch to innervate the sweat glands, vascular
  smooth muscle, the arrector pili muscle of hair
  follicles, and sebaceous glands

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Nerves and Receptors
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Appendages of the Skin
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Hair Follicle

• Functions
• 1. prevent heat loss
• 2. as a first line of defense
• 3. as a touch organ
• 4. a conduit in the delivery of scents
• secreted by the sebaceous and
• apocrine glands
• 5. an important component of the
• body image
• Hair follicles are distributed throughout the
  integument with the exception of the palms,
  soles, and portion of the genitalia (so-called
  glabrous skin)
• The highest density of follicles is on the scalp
  (about 100000 hair follicles), growth rate is
  about 1 cm/month

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Compartments of hair shaft and hair follicle
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The Hair Cycle

• Anagen 2-6 years, 85-90
• Catagen 2-3 weeks, less than 1
• Telogen 2-3 months, about 13
• Each follicle goes through the hair cycle 10 to
  20
• times in a lifetime

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Sebaceous glands

• The sebaceous glands go hand in hand with hair
  follicles.
• They are especially prominent with the hair
  follicles of the face, scalp, chest, and
  backthey are absent on non-hairy glabrous skin.
  
• Sebaceous glands, being holocrine glands, form
  their secretion by decomposition of their cells.
• As a child, these glands are small, but they
  enlarge and become active during puberty due to
  their androgen sensitivity.  

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Sweat Glands I

• Sweat glands reside in the dermis and produce a
  watery secretion.
• There are two types of sweat glands eccrine and
  apocrine.  
• 1. Eccrine Sweat Glands
• Anatomy Coiled secretory portion is located in
  the reticular dermis. Excretory ducts spirals
  upwards and opens onto the skin surface.
• Distribution all over our body, most dense on
  our axillae, palms, soles, and forehead.
• Nervous control The eccrine glands are under
  sympathetic cholinergic control.
• Composition Inorganic ions (NaCl, K, HCO3-),
  Lactate, Urea, Ammonia and Amino acids, Proteins
  and proteases, PH between 4-6.8

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Sweat Glands II

• 2. Apocrine
• Anatomy apocrine sweat glands open into hair
  follicles and are larger glands.
• Distribution They densely populate the axillae,
  perineum, and areolae. They are not functional
  until just before puberty.
• Nervous control The apocrine sweat glands are
  innervated by sympathetic adrenergic nerve
  fibers.
• Composition The sweat is generated by
  "decapitation" secretion of the gland's cells.
• The apocrine sweat is milky and viscid without
  order when it is first secreted. It is only after
  skin's bacteria has acted upon the apocrine sweat
  that it develops an odor.

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Eccrine Apocrine
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Nails

• A plate of hardened
• and densely packed keratin.
• Nail matrix is full of dividing
• cells which age, keratinize
• and progress forward to form
• the nail plate.

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Nails

• Nail plate is what we consider our "nail" and has
  a thickness of 0.3-0.5 mm and grows an average of
  0.1 mm/day. (fingernails do grow faster than
  toenails)
• Nail bed is just below the nail plate.
• Hyponychium is the thickened epidermis which is
  below the free edge of the nail.
• The pink color of the nail can be accounted for
  by dermal capillaries that are adjacent to the
  nail bed.
• The distal white lunula is basically the visible
  part of the nail matrix.  

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Primary skin lesions
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Macules

• A macule is a circumscribed, flat lesion that
  differs fromsurrounding skin because of its
  color.
• They may be the result of hyperpigmentation,
  hypopigmentation, vascularabnormalities,
  capillary dilatation (erythema), or purpura
  (extravasated redblood cells).

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Papule

• A papule is a small, solid, elevated lesion.
• Papules are generally smaller than 0.5 cm in
  diameter.

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Plaque

• A plaque is a mesalike elevation that occupies a
  relatively large surface area in comparison with
  its height above skin level

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Patch

• A patch is a portion of any surface
• markedly different in appearance or
• character from what is around it.
• Dermatologists have used thisterm in different
  ways some restrict its use to the description of
  very large macules others use it to refer to
  relatively thin but large plaques.

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Nodule

• A nodule is a palpable, solid, round or
  ellipsoidal lesion.
• Depth of involvement rather than diameter,
• differentiate a nodule from a papule.

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Wheals

• A wheal is a rounded or flat-topped papule or
  plaque that is characteristically evanescent,
  disappearing within hours.
• The epidermis is not affected there is no
  scaling.

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Vesicles and Bullae

• A vesicle is a circumscribed, elevated lesion
• that contains fluid.
• A bullae is a vesicle larger than 0.5 cm

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Pustule

• A pustule is a circumscribed, raised lesion that
  contains a purulent exudate.
• Pus, composed of leukocytes with or without
  cellular debris,may contain bacteria or may be
  sterile,

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Erosion and Ulcer

• An erosion is a moist, circumscribed, usually
  depressed lesion that
• results from loss of all or a portion of the
  viable epidermis.
• An ulcer is a hole in the skin in which there
  has been destruction
• of the epidermis and at least the upper
  dermis.

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Clinical signs
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Dimple sign

• Useful maneuver in differentiating dermatofibroma
  from melanoma.
• Application of lateral pressure with the thumb
  and index finger results in the formation of
  depression (dimple) in a dermatofibroma.

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Nikolskys sign

• It refers to the sheetlike removal of epidermis
  by gentle traction.
• Pemphigus vulgaris, Toxic epidermal necrolysis

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Dariers sign

• It refers to the development of an urticarial
  wheal in the lesions of urticaria pigmentosa afer
  they are rubbed.

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Auspitzs sign

• It refers to the appearance of pinpoint dots of
  blood at the tops of ruptured capillaries when
  scale is forcibly removed from psoriatic plaques.

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Examinations
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1. KOH Smear

• KOH digest the proteins, lipids, and most of the
  other epithelial debris present in the samples.
• Diagnosis
• 1. Fungual infection (dermatophyte,
• candidiasis, tinea versicolor)
• 2. Scabies
• 3. Pediculosis

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2. Woods light examination

• ?? Longwave ultraviolet light (320-400nm)
• ???????fluorescence
• Diagnosis
• 1. Fungual infection (ex. Tinea capitis, Tinea
  
• versicolor)
• 2. Bacteria infection (ex. Erythrasma)
• 3. Porphyria
• 4. Pigmentation (ex. Vitiligo and melasma)

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Woods light results

• Microsporum bright blue
• Malassezia furfur golden green
• Corynebacterium minutissimun coral red
• Pseudomonas yellowish green
• Porphyria pinkish-red
• Localize site of melanin (???????????,
  ?????????????)
• freckle and melasma ? darker
• Mongolian sacral spot ? lightening

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3. Tzanck Smear

• Diagnosis
• 1. Herpes virus infection Chickenpox,
  Herpes
• simplex, Herpes zoster
• 2. Bullous disease Pemphigus, Pemphigoid
• Procedure
• 1. ??????? base , ??????????
• 2. Lius stain
• Results
• 1. Herpes virus infection Multinucleated
  giant
• cells
• 2. Bullous disease ???kerationcyte????,
• ???keratinocyte????,????????
• ????????????????

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Multinucleated giant cells
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4. Patch test

• ?? To elicit an immune response by challenging
• already sensitized persons to define
  allergens
• assessing the degree of response
• Diagnosis allergic contact dermatitis
• Procedure ?allergens???????,??????,
• ?48hr???
• Results
• ? (Doubtful reaction) faint erythema
  only
• (Weak positive reaction) erythema,
  infiltration,
• 
  possibly papules
• (Strong positive reaction) erythema,
  infiltration,
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  papules, vesicles
• (Extreme positive reaction) intense
  erythema
• 
  and infiltration and
• 
  coalescing vesicles

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5. Biopsy of the skin

• Indication
• Biopsy is indicated in all suspected neoplasm
  and all dermatologic disorder in which diagnosis
  is not possible by clinical exam alone
• Type Scalpel biopsy ( incisional excisional ),
  Punch biopsy, Shave biopsy, Curratage

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Thanks for your attention