Skin
Functions
 There are four main functions: protection, sensation, thermoregulation, and
metabolism.
 Barrier to physical agents
 Protects against mechanical injury
 Prevents dehydration of body through fluid loss
 Reduces the penetration of UV radiation
 Helps regulate body temperature
 Provides a surface to grip
 Acts as a sensory organ
 Acts as an outpost for immune surveillance
 Plays a role in vitamin D production
 Has a cosmetic association
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Largest organ of the body
Anatomy
o Main cell- keratotinocyte
o Layers
 Epidermis
 This is a thin outer layer of epithelial cells, much of which
is made of keratin-containing cells of various shapes.
 As the lower layers form new cells, they are pushed
upward.
 Layers
o S. corneum
 Outer functional layer of the skin.
Composed of dead, flattened, anuclear cells
with the cytoplasm filled with keratin
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(keratinized stratified squamous epithelium)
matted together.
S. lucidem
 May not be apparent. Seen especially in
areas of thick skin as a clear layer (several
cell layers thick) in which cells are
extremely flattened and not individually
distinguishable.
S. granulosum
 Cells become flatter in appearance. Contains
basophilic granules of keratohyaline.
S. spinosum
 Several cell layers, often referred to as
prickle cells (prickle cell layer).
S. germinativum
 Aka S. basale
 The germination zone. This is the most
internal.
 This is a single layer of columnar or
cuboidal germinal cells (keratinocytes)
resting on a absement membrane, separating
the dermis and the rest of the epidermis.
Melanocytes are sandwiched in between.
These function in skin pigmentation, are of
neuroectodermal in origin, and are usually
found in the stratum basale or occasionally
in the stratum spinosum.
Dermis
 Thick, tough, and flexible. Provides support to the
epithelium.
 Contains connective tissue cells, elastic fibers, blood
vessels, lymph vessels, occasional smooth muscle cells,
sensory nerve endings, and skin appendages (epithelial
derivatives embedded in the dermis) such as hair follicles,
nails, sebaceous glands, and sweat glands.
 Dermal papillae, upward projections toward the epidermal
surface, are usually apparent.
 Hypodermis
 Also called the subcutaneous layer.
 Loose connective tissue
 Contains various amounts of adipose tissue, nerve, endings,
and blood vessels larger than those in the dermis.
o Cutaneous Glands
 Sebaceous Glands (Holocrine)
 These are simple branched alveolar glands embedded in the
dermis.
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One or more are associated with each hair follicle.
Located in the dermis. Secrete sebum, which acts as a
waterproofing agent on the hair and skin surface.
 May be independent of hair follicles in areas such as the
lips, nipples, eyelids (Meibomian glands).
 Sweat glands
 Merocrine
o Simple coiled tubular glands with secretory portion
located in the dermis or hypodermis. Found over
most of the body. Secrete a watery substance upon
cholinergic stimulation. Secretions are discharged
by exocytosis. Myoepithelial cells function in cell
discharge.
 Apocrine
o Coiled tubular glands with a large lumen with
secretory portion ocated in the hypodermis. Glands
usually associated with hair follicles. Found
especially in the axillae and genital regions. Found
in eyelids as the glands of Moll. Secretory products
are enclosed in portions of membrane from the
apical end of the cell and are pinched off.
o Vessels
 Arteries supplying the skin are located deep in the hypodermis
from which they give rise to branches passing upwards to form two
plexi of anastomosing vessles. The cutaneous plexus is deep. It is
located near the dermal-hypodermal junction. The papillary plexus
is superficial, just below the dermal papillae.
 Venous drainage is similar. Numerous arterio-venous shunts
(communications) are important for thermoregulation.
 The skin has a rich lymphatic drainage system which begins in the
papillae and communicates with a network of larger lymph vessels
in the subcutaneous tissue.
o Nerves
 Nerve endings or specialized cells which convert stimuli from the
external or internal environment into afferent nerve impulses.
 Types
 Meissner’s corpuscles (light touch, touch discrimination)
 Pacinian corpuscles (deep pressure and vibration)
 Merkel’s disk (fine, continuous touch)
 Ruffini corpuscle (stretch in skin, heat)
 Krause’s end bulb (pressure, cold)
 Golgi tendon organ (tension in tendons)
 Muscle spindles (stretch in muscle)
Histogenesis
o Formation and differentiation of ectoderm and endoderm in the embryonic
period.
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The blastoderm is a single layer of cells of the blastula stage of the
embryo.
After formation of the blastula in early development, during
gastrulation, the cells of the “inner cell mass” (blastoderm) become
organized and form the embryonic disc. The embryonic disc is
seen as having two layers of cells which represent early primary
germ layers- ectoderm and endoderm. Most of the epithelial organs
are derived from these germ layers.
The outermost germinal layer is the ectoderm which gives rise to
the skin epidermis and nervous system. This includes the skin
epidermis (extends into the mouth and anal canal), corneal
epithelium and lens, tooth enamel, and specialized sensory
epithelia of the nose and internal ear. This layer covers the entire
external surface of the body. By invagination and proliferation, this
outer covering epithelium gives rise to tubes or solid cords that
form the glandular appendages of the skin (sebaceous and
mammary glands).
The endoderm layer produces the epithelial linings of the digestive
and respiratory systems, epithelial linings of the urethra and
bladder, endocrine gland structures (thyroid, thymus), portions of
the liver and pancreas.
The mesenchymal layer forms skeletal, smooth, and cardiac
muscle.
Physiology
o Cells are continually sloughed off.
o Collagen goes in all directions for support
o In pigmented skin, the epidermis is darker.
Primary skin lesions
 Solid
o Macule
 Flat. They cannot be palpated.
 Circumscribed, small (<1cm), discolored
 Various colors due to cause
 Hyper or hypopigmented
 Erythematous- red from vascular dilation
 Age spots
 Large = Patch
o Papule
 Palpable
 <1cm
 Superficial
 Due to deposits, infiltrates from infection, etc.
o Plaque
 Papule >1cm
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Elevated
Raised, broad, and palpable.
Ex. Psoriasis
Fluid
o Vesicle
 Filled with fluid
 <5mm (Small blister)
 Can contain serous fluid (clear) or lymph, blood, etc.
 Usually visible
 Has the ability to open and fluid can leak out.
 Can break very easily if superficial
 Can be in various layers
o Bulla
 Blister >5mm
 Can be single or multiple compartments
o Pustule
 Contains pus (infectious/inflamed)
 Different sizes and shapes
 Red outside/white inside. Color may vary.
o Wheal
 Temporary depressable swelling of the dermis.
 Edematous
 Sharp borders, but not stable.
 Redness
 Enough swelling compresses the blood vessels and it looks white.
 Round, raised with flat top.
 Goes away in a few hours.
 An eruption of wheals is termed urticaria and it usually itches
 “Hives”
o Nodule/tumor
 Solid lesion under the skin.
 >1cm
 Palpebal, under the dermis, in the dermis or epidermis.
o Cyst
 Raised
 Lined in a capsule, so it is firm
 Fluid inside
 Common: epidermal cysts
Secondary Skin Lesions
 Result from external factors: scratching, trauma, etc.
 Scale
o Epidermal thickening
o Primary- Plaque/ Secondary- Scaling
o Sloughing off of epidermis
o Seen in psoriasis, pideriasis, and ecteniosis
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Crust
o Material (dried fluid) on a primary lesion
o Potential causes- infection
o Thick or thin layer
o Yellow- serum
o Yellow/green- pus
o Dark brown- blood
o Seen in impetigo
Fissure
o Crack or split of the epidermis
o Due to external
o Chelatus- infected fissure
Erosion
o Superficial loss of epidermis
o After a bulla breaks
o Usually moist, circumscribed, and depressed
Ulcer
o Deeper erosion (to dermis)
o Impairment of vascularization
o Red dots- granulation  healing from bottom up.
o Poor circulation needs vascular bypass
Lichenification
o Thickened skin (epidermal lining)
o Caused by rubbing/scratching
o Seen with chronic eczema.
Excoriation
o Scratch marks
o Seen prior to lichenification
Atrophy
o Loss of dermis, epidermis, or both.
o Result of aging.
o Epidermis looks paper thin.
Scar
o Aka keloids
o An increase in normal tissue with fibrous tissue at the site of injury or
dermis, not epidermis.
Epidermal atrophy
Dermal atrophy
Pathology
 Hyperkeratosis
o Thickening of the S. corneum
o Ex. Lichenification
 Acanthosis
o Increase in spinous layer
o Seen more with psoriasis
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Spongiosis
o Aka spongiotic edema
o Swelling of the skin with fluid trapped beneath
o Seen with contact dermatitis
Acute Inflammatory Dermatosis
o Urticaria
 Pretty common
 Due to allergies (localized degranulation of mast cells causing
fluid to come out), extreme temperatures, etc.
 Fluid trapped in the skin
 Vasodilation and superficial dermal edema
o Angioedema
 Hives around the eyes and mouth
 Acute
 Deeper swelling into the reticular dermis
 Primary question:
 Are you taking ACE inhibitors for HTN, trauma, etc.
 Can also be a reaction to something
 Treat with epinephrine
 Associated with systemic conditions
o Dermatographism
 Physical urticaria
 Goes away in 15-30 minutes
 Dermal inflammation from physical rubbing.
 Treat with antihistamines
o Acute eczematous dermatitis
 Allergic contact dermatitis
 Spongiotic
 Red, itchy, swollen
 Not contagious unless haptens are still on the skin.
o Kebner Phenomenon
 While the hapten is still on the skin, lesions
can occur with a scratch, etc.
 From allergens
o Rhus- Poison ivy, oak, sumac
o Nickel
 Can lead to Lichen Simplex Chronicus
o Due to chronic allergic dermatitis, neural dermatitis,
etc.
o Skin thickens (acantosis), hyperpigmentation, and
hyperkeratitis.
 Irritant contact dermatitis
 Due to chemical and physical agents
 Washing too much (not just allergic)
 Dry, fissuring, redness, and spongiosis
 Breakdown in skin permeability barriers
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Atopic dermatitis
 Prone to allergies
 Classic eczema without cause
 Mainly on cheeks
 Overreactive skin (dry, red, itchy)
 Genetic/idiopathic- more common with allergies and
asthma
 Treatment: moisturizer/corticosteroids
 Infantile Eczema
o Birth  2 years
o More general in adulthood.
o Found in folds, causing a risk of secondary
infections
Erythema Multiforme Minor
 Self-limited
 Hypersensitivity
 Epithelial cell damage/necrosis, if severe
 Reaction to drugs, infections, etc.
 “Target appearance”
o Swollen in the middle
o Macule or papule
Erythema Multiforme Major
 Aka Stevens-Johnson Syndrome
 Seen with a reaction to sulfa, penicillin, phenylbarbitol, etc.
 Also affects the mucous membranes
o Erosion and peeling
 Can lead to secondary infections
 Mortality 1/3
Toxic Epidermal Necrolysis
 Worst form of EM
 Death of entire epithelium
 Sloughs off
 Necrotic tissue is black.
 Treatment: supportive
 Less than 50% survive
Chronic Inflammatory Dermatoses
 Psoriasis
o On extensor surfaces
o Not contagious
o Most have plaques/scaling
o On scalp, trunk, limbs, nails
o Increase dermal turnover, therefore scaling.
o Genetic
o Flare with systemic and environmental factors
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o Treatment
 Non-pharmacologic
 Medicines
 Corticosteroids
 Coal tar (in shampoo)
 Keratolytic agents
o To increase peeling
 Vitamin D analogs
 Topical retinoids
 UVA and Psoralin (PUVA)
 Moisturizers
Lichen Planus
o Common
o Ouritic
o Purplish
o Polygonal
o Papules
o Itchy
o Chronic
o Cell-mediated immune response
 Usually associated with other diseases (Hep C)
o Hyperpigmentation can stay
o Wickim Striae- white lines that go across with coalation
Blistering (Bullous) Diseases
 Pemphigus
o Big blisters
o Get a biopsy
o Due to no reason
 Bullous Pemphigoid
o Bad
o Big blisters
o Get a biopsy
o Due to no reason
 Dermatitis Herpetiformis
o IgA- related immune reaction
o Associated with seliac disease
 Problem with bowels
 Reaction with glutan, wheat, etc. leads to diarrhea
o Itchy, on extensor surfaces
o “Looks like herpes”, but it is not viral.
o Vesicles are generally without a pattern.
o Treat with Dapsil
Tumors
 Benign and premalignant epithelial lesions
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o Seborrheic keratosis
 Pigmented skin growths
 Common with aging
 “Oily scales”
 Benign
 In those over 40
 Even color and contour
 Nice, smooth, round
 Waxy
 Can be peeled off, but reappear
o Keratoacanthoma
 Cup-shaped lesion with central raising
 Keratin in middle
 Common with skin damage
 Rapid growth
 Can leave on own
 Benign/ no metastasis
 “Hard”
o Verrucae (Warts)
 Can cause BCC, but very rare
 Benign epithelial tumors
 Can be from HPV
o Actinic Keratosis
 Premalignant
 Rough papule with scales
 Without treatment, can go to SCC
 Treat with liquid nitrogen
 On sun damaged areas
 Increased risk with fair skin
 Red/dark pigmented
 If all over, a cream is available
 Corticosteroids to decrease the redness
o Dermatofibroma
 Benign fibrous scar tissue from the dermis
 Goes down with stretching the skin (diagnostic)
 Usually due to injury
Malignant Epidermal Tumors
o SCC
 No nodules
 Flat
 More with elderly (60-80)
 Thick, injurated plaque
 Can ulcerate
 In sun exposed areas
 Irregular, red, scaly
 Can be from untreated actinic keratosis
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o BCC
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Local
No metastasis
Bowen’s Disease
 SCC in situ. Has not spread through the basement
membrane
Common
Sun induced
Translucent papule
Can have firm nodules and abnormal blood vessels along the
surface.
 Asymptomatic
 In fairer skin
 Younger (40-60s)
 Local invasion only. No metastasis
 Grows slowly
 But it may be deeper (can have extensions under the skin, therefore
hard to remove)
 Treatment: Moh’s Procedure
 Look at pieces of skin and treat layer by layer.
Tumors of Melanocytes
o Nevocellular nevus
 Nevi (Moles)
 Most common neoplasm
 Benign
 Melanocytes on basal layer
 Most acquired
o Can be congenital
o Have all by about 35 years.
o Suspicious if obtained late in life.
 Types
o May be a progression
o Junctional
 Most common
 2-5mm
 Even pigmented/contour
 Acquired after 1 year
 Rare to see as we age
 No bleeding or symptoms
 Do not change
 On sun-exposed skin
 At epidermis/dermis junction
 More pigment than a freckle
 Biopsy if >35 years, not even, bleeding, or
symptoms.
o Compound
 Intermediate
o Intradermal
 Least common
 Dome-shaped
 Popular
 Less pigmented
 Only in epidermis
 Melanocytes are in the dermis
 Usually on hand, neck, or scalp
 Congenital Nevus
 Present at birth and grows with the person
 Usually >1cm
 Usually hair from them
 No symptoms
 Increased risk of melanoma (proportional to size)
 5% chance
 Can be removed
 Benign with even color and contour
 Bathing Trunk
o Concentration of melanin
o 30% risk of cancer
o Needs to be removed
 Skin grafting, etc.
o Dysplastic Nevus Syndrome
 In kids
 Increased number of nevi with increased size
 Periphery changes color
 Irregular borders, uneven surface
 Genetic
 On backs
 100% risk of melanoma
 Need to monitor
o Malignant melanoma
 Metastases- threat
 Sun exposed areas
 Males- upperback/ females- legs
 Can also be found on the retina, mucous membranes, etc.
 1% of the population get this
 Types
 Superficial Spreading Melanoma
o Most common (65%)
o At dermo-epidermal junction
o Grows at horizontal plane (grows out) = radial
growth
o Macular, slightly elevated
o Then grows deep (depth related to prognosis)
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Nodular Melanoma
o Lumpy
o Rapidly growing
o Grows up and down
o Worse prognosis because it is the dermis.
o Less common
o Firm nodules
o Difficult to treat
 Lentigo Malignant Melanoma
o “Age/liver spot” looking
o In situ melanoma at 1st.
o Spreads superficially (5-7cm)
o Better prognosis, but difficult to remove, because it
is big.
 Acrolentiginous Melanoma
o Rare
o At muco-cutaneous junctions (not sun exposed
areas)
 Lip, vagina, anus, nails, palms, feet
o Can be spontaneous
o More with pigmented skin (AfrinaAmericans/Asians)
o Horizontal and vertical growth
o 2nd worse
Diagnosing Melanomas
o ABCs
 Asymmetric
 Border Irregular
 Color Uneven
 Diameter >6mm (pencil eraser)
 Elevation
o Rule 1
 Lots of skin lesions have pigment, but beware of irregular color
and contour.
o Rule 2
 Lots of pigmented lesions grow, but beware of irregular growth
and lack of symmetry, especially with a positive family history.
o Rule 3
 Just about everyone gets moles, but beware of moles that grow late
in life.
o Rule 4
 There are lots of moles, but beware of moles that are large
 Make an incisional biopsy to the subcutaneous fat.
o Rule 5
 “When in doubt, cut it out”