Seven Functions of SkinSeven Functions of Skin

► Mechanical/Chemical Mechanical/Chemical damagedamage – keratin – keratin toughens cells; fats toughens cells; fats cells cushion blows; cells cushion blows; and pressure receptors and pressure receptors measure damagemeasure damage

► Bacterial damageBacterial damage – skin – skin secretions are acidic secretions are acidic and inhibit bacteria. and inhibit bacteria.

► Ultraviolet radiationUltraviolet radiation – – melanin produced to melanin produced to protect from UV protect from UV damagedamage

Thermal controlThermal control – – regulates body regulates body temperaturetemperature Heat lossHeat loss: sweat to : sweat to

cool the skincool the skin Heat retentionHeat retention: :

prevents blood from prevents blood from losing heat & losing heat & shiveringshivering WaterproofingWaterproofing – contains lipids to – contains lipids to

prevent drying outprevent drying out

Excretion of wasteExcretion of waste – urea and uric – urea and uric acid secreted in sweatacid secreted in sweat

Makes vitamin DMakes vitamin D – changes – changes cholesterol molecules in skin and cholesterol molecules in skin and

converts it to vitaminconverts it to vitamin D D

Skin Skin StructureStructure►EpidermisEpidermis — outer layer — outer layer

►Dermis Dermis – middle layer– middle layer►Subcutaneous tissue Subcutaneous tissue – deepest – deepest

layerlayer also referred to as the ‘also referred to as the ‘hypodermishypodermis’’

EpidermisEpidermis

Summary of layers from Summary of layers from deepest to most deepest to most superficial:superficial:

Stratum basaleStratum basale Stratum spinosumStratum spinosum Stratum Stratum granulosumgranulosum Stratum lucidum Stratum lucidum Stratum corneumStratum corneumA cell takes 40 – 56 days from creation to

sloughing off

►Stratum basaleStratum basale Deepest layer of epidermisDeepest layer of epidermis Cells actively undergoing cell divisionCells actively undergoing cell division New cells push older cells upward until they New cells push older cells upward until they

eventually fall offeventually fall off Cells are mostly Cells are mostly keratinocyteskeratinocytes and some and some

melanocytesmelanocytes

Layers of the EpidermisLayers of the Epidermis

KeratinizationKeratinization► KeratinKeratin is a protein that helps harden skin cells, is a protein that helps harden skin cells,

makes them tougher and helps prevent water makes them tougher and helps prevent water loss by the body.loss by the body.

► KeratinocytesKeratinocytes are areresponsible for responsible for making keratinmaking keratin

Keratin is found in cells of the basale and

spinosum strata

Keratin makes the skin waterproof

► Stratum spinosumStratum spinosum – – Made of Made of keratinocyteskeratinocytes Some cells grow Some cells grow

projections that projections that connect to other connect to other cells making the cell cells making the cell layer strongerlayer stronger Prickle Cells with long

projections

Stratum granulosumStratum granulosum – – mostly flattened mostly flattened keratinocytes that have lost keratinocytes that have lost nuclei and organellesnuclei and organelles

Death zone of Death zone of keratinocyteskeratinocytes

Vitamin D ProductionVitamin D Production►Cells of stratum spinosum and basale:Cells of stratum spinosum and basale:

UV energy + cholesterol = Vitamin DUV energy + cholesterol = Vitamin D►Vitamin DVitamin D::

used by kidney to make the hormone used by kidney to make the hormone calcitriolcalcitriol

►CalcitriolCalcitriol:: necessary to signal small intestine to absorb necessary to signal small intestine to absorb

calcium from the bloodcalcium from the blood►No Vitamin D No Vitamin D no calcitriol no calcitriol no calcium absorption no calcium absorption weak bones weak bones

► Stratum lucidumStratum lucidum Formed from dead cells of Formed from dead cells of

the deeper layersthe deeper layers Occurs only in thick, Occurs only in thick,

hairless skin of the palms hairless skin of the palms of hands and soles of feetof hands and soles of feet

► Stratum corneumStratum corneum Outermost layer of Outermost layer of

epidermisepidermis Scale-like dead cells are Scale-like dead cells are

filled with filled with keratinkeratin which is which is a strengthening protein a strengthening protein also preventing water loss also preventing water loss from skinfrom skin

Layers of SkinLayers of Skin

No Lucidum Layer

MelaninMelanin

► Pigment (melanin) Pigment (melanin) produced by melanocytesproduced by melanocytes

► Melanocytes are mostly in Melanocytes are mostly in the stratum basalethe stratum basale

► Color is yellow to red to Color is yellow to red to brown to blackbrown to black

MelanocytesMelanocytes: Cells deep in the epidermis : Cells deep in the epidermis and dermis that produce a pigment called and dermis that produce a pigment called melanin which protects the cells from UV melanin which protects the cells from UV damagedamage

Skin color determined by the size and quantity of melanin

granules in the tissue

► Determined by genetic, environmental, and physiological Determined by genetic, environmental, and physiological factorsfactors Your DNA determines how much MELANIN is producedYour DNA determines how much MELANIN is produced UV radiation increases melanin productionUV radiation increases melanin production Circulation, vitamin deficiencies, physical ailments Circulation, vitamin deficiencies, physical ailments

(liver failure)(liver failure)

What’s your color?What’s your color?

Why the Why the Spots…?Spots…?

► Large amounts of Large amounts of melanin occur in some melanin occur in some regions like freckles, regions like freckles, moles, and nipples.moles, and nipples.

► Caused by uneven Caused by uneven distribution of melanindistribution of melanin

► Less melanin occurs in Less melanin occurs in the lips, hands, and the lips, hands, and soles of the feet.soles of the feet.

AlbinismAlbinism► A single gene mutation can cause a A single gene mutation can cause a

deficiency or complete absence of melanin.deficiency or complete absence of melanin.► Albinos have fair skin, white hairs, and Albinos have fair skin, white hairs, and

unpigmented eyes (eyes appear red)unpigmented eyes (eyes appear red)

FingerprintsFingerprints

The up and down border between the dermis and epidermis helps bond the layers together In thick skin, epidermal ridges show on the surface as fingerprints: Function – enhance gripping

Dermis – the middle layerDermis – the middle layer► Papillary layer:Papillary layer:

Thin (20%)Thin (20%) Consists:Consists:

►Contains dermal papillaeContains dermal papillae►Capillaries, sensory neuronsCapillaries, sensory neurons

Function: feed epidermisFunction: feed epidermis

► Reticular Layer:Reticular Layer: Thick (80%)Thick (80%) Consists:Consists:

►Elastic and Collagen fibersElastic and Collagen fibers► Sweat and oil glandsSweat and oil glands► Deep pressure receptorsDeep pressure receptors

Function: provide strength and flexibilityFunction: provide strength and flexibility

Dermal Dermal PapillaePapillae► small, nipple-like small, nipple-like

extensions of the extensions of the dermis into the dermis into the epidermis epidermis

► Blood vessels Blood vessels nourish all hair nourish all hair follicles and bring follicles and bring nutrients and oxygen nutrients and oxygen to the lower layers of to the lower layers of epidermal cells epidermal cells

What makes us stay young What makes us stay young looking?looking?

►Elastic fibersElastic fibers gives skin elasticitygives skin elasticity fibers can stretch up to 1.5x fibers can stretch up to 1.5x

their length and snap back their length and snap back to their original length to their original length when relaxed when relaxed

►Collagen fibersCollagen fibers gives skin support/firmnessgives skin support/firmness ~ one quarter of the human body is collagen~ one quarter of the human body is collagen support the skin’s mechanical strength and support the skin’s mechanical strength and

texturetexture

Sensory Perception in SkinSensory Perception in Skin► Skin is highly sensitivity to touch Skin is highly sensitivity to touch

because of large amounts of because of large amounts of sensory structures found in dermissensory structures found in dermis

Sensory Sensory Perception in Perception in

DermisDermisMerkel cells:Merkel cells: deep layers of epidermis deep layers of epidermis

- superficial touch superficial touch

Free Nerve Endings:Free Nerve Endings: superficial dermis superficial dermis- pain and temperaturepain and temperature

Meissner’s Corpuscles:Meissner’s Corpuscles: superficial dermis superficial dermis- light touchlight touch

Pacinian Corpuscles:Pacinian Corpuscles: deep dermis deep dermis

- pressure and vibrations- pressure and vibrations

Skin StructureSkin Structure► Subcutaneous tissueSubcutaneous tissue (hypodermis)(hypodermis) is deep to is deep to

dermisdermis Not part of the skinNot part of the skin Anchors skin to underlying organs, bones and Anchors skin to underlying organs, bones and

musclesmuscles Contains half of the body’s fat; acts as padding Contains half of the body’s fat; acts as padding

and insulation.and insulation.