Anatomy and Anatomy and Physiology of the Physiology of the

SkinSkin

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Structure of skinStructure of skin11 EpidermisEpidermis22 Basement membrane (dermoepidermal junction)Basement membrane (dermoepidermal junction)33 DermisDermis44 Subcutaneous fatSubcutaneous fat

Epidermis: Four layers (from outside – inside)Epidermis: Four layers (from outside – inside)1.1. Cornified layerCornified layer2.2. Granular layerGranular layer3.3. Spinous layerSpinous layer4.4. Basal layerBasal layer

Dermis contains:Dermis contains:Collagen fibersCollagen fibersElastic fibersElastic fibersGround substancesGround substancesBlood vesselsBlood vesselsNerves.Nerves.

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Skin appendages:Skin appendages:

Hair follicleHair follicle

Sebaceous glandSebaceous gland

Arrector pili muscleArrector pili muscle

Eccrine sweat glandEccrine sweat gland

Apocrine sweat glandsApocrine sweat glands

NailNail

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Dermatology deals Dermatology deals with disorders of with disorders of skin, hair, nails, and skin, hair, nails, and mucous membranesmucous membranes..

StructureStructureEpidermisEpidermis (thinner outer (thinner outer layer of skin)layer of skin)Dermis Dermis (thicker (thicker connective tissue connective tissue layer)layer)HypodermisHypodermis (subcutaneous (subcutaneous layer)layer)

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Dermatological disorder = 10% -Dermatological disorder = 10% -15% of primary care consultations15% of primary care consultationsSkin is the largest organ in human Skin is the largest organ in human bodybodyDermatological diseases can cause Dermatological diseases can cause social and psychological problems, social and psychological problems, also it may affect ability to work also it may affect ability to work (e.g. Chronic hand dermatitis.)(e.g. Chronic hand dermatitis.)Skin is the gate of the body(might Skin is the gate of the body(might reflect systemic disease).reflect systemic disease).

Physiology (function)Physiology (function)1- Protection1- Protection

- physical barrier that protects - physical barrier that protects underlying tissues from injury, UV underlying tissues from injury, UV light and bacterial invasion.light and bacterial invasion.

- mechanical barrier and - mechanical barrier and immunityimmunity

2- Excretion2- Excretion - sweat removes water and small - sweat removes water and small

amounts of salt, uric acid and amounts of salt, uric acid and ammonia from the body surfaceammonia from the body surface

3- Synthesis of Vitamin D3- Synthesis of Vitamin D

4- Regulation of body temperature4- Regulation of body temperature- high temperature or strenuous - high temperature or strenuous

exercise; sweat is evaporated from exercise; sweat is evaporated from the skin surface to cool it down.the skin surface to cool it down.

- - vasodilationvasodilation (increases blood (increases blood flow) andflow) and vasoconstriction vasoconstriction (decrease in blood flow) regulates (decrease in blood flow) regulates body temp.body temp.

5-Sensation5-Sensation - nerve endings and receptor - nerve endings and receptor

cells that detect stimuli to temp., cells that detect stimuli to temp., pain, pressure and touch.pain, pressure and touch.

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11 EpidermisEpidermis22 Basement Basement

membrane membrane (dermoepider(dermoepidermal junction)mal junction)

33 DermisDermis44 SubcutaneouSubcutaneou

s fats fat

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Stratum lucidum :Stratum lucidum :

Found in thick Found in thick skin of palms skin of palms and soles above and soles above granular layer granular layer

Epidermis: Consist of several Epidermis: Consist of several zoneszones

Cornified layer (Stratum Cornified layer (Stratum corneum )corneum )

Granular layer (Stratum Granular layer (Stratum granulosum)granulosum)

Spinous layer (Stratum Spinous layer (Stratum spinosum)spinosum)

Basal layer (Stratum basale) Basal layer (Stratum basale)

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Basal layerBasal layer Rest on the basement Rest on the basement membrane they divide membrane they divide continuously and move continuously and move upwards.upwards. Melanocytes are Melanocytes are

dendritic dendritic cells lying between basal cells lying between basal cells in a ratio of 1:10 .cells in a ratio of 1:10 .Melanocytes synthesize Melanocytes synthesize melanin stored in melanin stored in melanosomes.melanosomes.

Basal Cell layerBasal Cell layer Melanosomes are Melanosomes are transferred to adjacent transferred to adjacent

cells cells forming the Epidermal forming the Epidermal Melanin unit.Melanin unit. Small, unmelanized, Small, unmelanized, clumped melanosomes are clumped melanosomes are found in white skinfound in white skinLarge melanized, Large melanized,

dispersed dispersed melanosomes in dark skinmelanosomes in dark skin

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The Spinous cell layer:The Spinous cell layer: Usually 5 -10 layers Usually 5 -10 layers

thick .thick .

Adhere to each other Adhere to each other by by

desmosomes (complex desmosomes (complex

modification of the cell modification of the cell

membrane ). membrane ). Desmosomes Desmosomes

appear like spines.appear like spines.

Granular Cell layer :Granular Cell layer : Diamond Diamond

shaped cells.shaped cells.

Cytoplasm is filled with Cytoplasm is filled with

keratohyaline granules.keratohyaline granules. In thin skin it is 1 -3- In thin skin it is 1 -3-

cell layers and 10 cell layers and 10 cell layers in thick cell layers in thick skin like palms and skin like palms and soles.soles.

Stratum Corneum layerStratum Corneum layer: : The cells in this layer The cells in this layer

have no nucleous .have no nucleous . Cells have thick Cells have thick

envelope envelope that resist chemicals.that resist chemicals.

Cells are held Cells are held together by together by

desmosomes.desmosomes. It is 25 cell layer .It is 25 cell layer .

Basement MembraneBasement Membrane (BM(BM))

Pink homogenous area Pink homogenous area between epidermis between epidermis and dermis .and dermis .

Consists of number of Consists of number of proteins like BP proteins like BP

antigens, collagen 4antigens, collagen 4 The site of attack The site of attack

injury injury in blistering diseases.in blistering diseases.

Skin StructureSkin Structure

Components of BMComponents of BM

Lamina lucida: thin Lamina lucida: thin

clear amorphous spaceclear amorphous space Lamina densa: an Lamina densa: an

electron dense area electron dense area containig type4 containig type4 collagencollagen

Anchoring fibrils : Anchoring fibrils : anchors epidermis to anchors epidermis to dermis ,type 7 dermis ,type 7 collagen collagen

Skin StructureSkin Structure

Dermis is divided intoDermis is divided into

Papillary dermis .Papillary dermis .

Reticular dermisReticular dermis Consists ofConsists of ::

Collagen fibers Collagen fibers Provides Provides strength .strength .

Elastic FibersElastic Fibers::

Provides elasticity, Provides elasticity,

protection against protection against shearing shearing

forces.forces.

Skin StructureSkin Structure

Ground substanceGround substance : :Binds water and Binds water and

maintains maintains the skin turgor.the skin turgor. Blood vesselsBlood vessels:: To nourish the To nourish the

overlying overlying epidermis.epidermis.

Skin StructureSkin Structure

The function of dermisThe function of dermis:: It provides It provides

nourishment to the nourishment to the epidermis and epidermis and interact with it interact with it during wound during wound repair.repair.

It gives the skin its It gives the skin its strength elasticity, strength elasticity, and softness.and softness.

Skin structureSkin structure

Subcutaneous Fat: Subcutaneous Fat:

Composed of Composed of lipocyteslipocytes

Skin Structure Skin Structure

Skin Appendages Skin Appendages includeinclude::

Eccrine/ apocrine Eccrine/ apocrine sweat sweat

glands.glands. Sebaceous glands.Sebaceous glands. Hair Follicles.Hair Follicles. NailsNails

Skin appendagesSkin appendagesEccrine sweat Eccrine sweat

glandsglands Tubular structures Tubular structures

open open

freely on the skin ;not freely on the skin ;not

attached to hair follicles.attached to hair follicles.

Under the influence of Under the influence of

cholinergic stimuli.cholinergic stimuli.

Skin appendagesSkin appendagesEccrine sweat Eccrine sweat

glandsglands Present everywhere Present everywhere

except except

the vermilion border ; the vermilion border ; nail nail

beds ; labia minora ; beds ; labia minora ; glans glans

Abundant in palms ; Abundant in palms ;

solessoles..

Skin appendagesSkin appendages

Apocrine glands:Apocrine glands:

Present in the axillae ; Present in the axillae ;

anogenital area anogenital area modified modified

glands in the external glands in the external ear ear

canal the eye canal the eye lids(moll’s lids(moll’s

glands ) and areolae.glands ) and areolae.

Sebaceous glands:Sebaceous glands: Attached to hair Attached to hair

follicles; or open freely.follicles; or open freely. Present in the scalp ; Present in the scalp ;

forehead face upper forehead face upper chest except palms and chest except palms and soles. soles.

Under the control of Under the control of androgens.androgens.

Ectopic glands in the Ectopic glands in the mucous mucous

membrane are called membrane are called fordyce spots.fordyce spots.

Sebaceous glandsSebaceous glands::.. Present in the areola as Present in the areola as Motgomery’s Motgomery’s

tubercles ;in the tubercles ;in the eye lids as Meibomian eye lids as Meibomian

glands.glands.

Skin appendagesSkin appendages

Hair follicles:Hair follicles: The hair follicle with The hair follicle with

it’s it’s attached sebaceous attached sebaceous

gland gland form the Pilosebaceous form the Pilosebaceous Unit.Unit. Structure :Structure :Infundibulum : Region Infundibulum : Region

between skin surface between skin surface and sebaceous gland.and sebaceous gland.

Skin Appendages Isthmus begin at

sebaceous glands and end at

bulge (site of insertion of arrector

pilli muscle) Hair bulb

envelopes the dermal papilla

Skin Appendages

Arrector pili is Arrector pili is smooth muscle smooth muscle located in the located in the dermis and is dermis and is attached to the side attached to the side of the hair shaft.of the hair shaft.

- Cold and emotions - Cold and emotions will contract muscle will contract muscle and pull hair in and pull hair in vertical position.vertical position.

Skin Appendages

Hair shaft has: Cuticle Cortex contain

pigment cells Medulla found only

in terminal hair

Skin appendages:Skin appendages:

Nails AnatomyNails Anatomy Nail plate made up Nail plate made up

of dead keratinized of dead keratinized cells of matrix.cells of matrix.

Nail bed is visible Nail bed is visible through nail plate.through nail plate.

Nail matrix lies Nail matrix lies above the above the midportion of distal midportion of distal phalanx phalanx

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Skin appendages:Skin appendages:

The lunula is the The lunula is the visible part of the visible part of the matrixmatrix

Proximal nail fold Proximal nail fold can be can be

altered in connective altered in connective tissuetissue

Fingernails grow 3 Fingernails grow 3 mm/mmm/m

Toenails grow 1 Toenails grow 1 mm/mmm/m

CornificationCornification (keratinization(keratinization))

Occur in the Occur in the cytoplasm of cytoplasm of epidermal epidermal keratinocytes keratinocytes during their during their terminal terminal differantiation into differantiation into dead horny dead horny cell(corneocyte)cell(corneocyte)

CornificationCornification (keratinization(keratinization))

The total process The total process takes takes

approximately 2 approximately 2 months.months.

It involves the It involves the formation of keratin formation of keratin polypeptides.polypeptides.

Abnormalities in this Abnormalities in this process leads to process leads to roughness and scaling roughness and scaling of the skin e g of the skin e g psoriasis.psoriasis.

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Skin immune systemSkin immune system

Langerhans cells Langerhans cells interact with interact with keratinocytes, keratinocytes, which secrete a which secrete a number of number of immunoregulatinimmunoregulating cytokines, and g cytokines, and T-cells forming T-cells forming the skin immune the skin immune system.system.

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