Skin Functions of SkinSkin Functions of Skin►Mechanical/Chemical damageMechanical/Chemical damage – keratin – keratin

toughens cells; fats cells cushion toughens cells; fats cells cushion blows; and pressure receptors to blows; and pressure receptors to measure possible damagemeasure possible damage

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

►Ultraviolet radiationUltraviolet radiation – melanin – melanin produced to protect from UV damageproduced to protect from UV damage

Skin FunctionsSkin Functions► Thermal controlThermal control – regulates body temperature – regulates body temperature

Heat lossHeat loss: sweat to cool the skin: sweat to cool the skin Heat retentionHeat retention: prevents blood to rush into : prevents blood to rush into

capillary bedscapillary beds

►WaterproofingWaterproofing – contains lipids to prevent – contains lipids to prevent drying outdrying out

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

►Makes vitamin DMakes vitamin D – modifies cholesterol – modifies cholesterol molecules in skin and converts it to vitamin Dmolecules in skin and converts it to vitamin D

Skin StructureSkin Structure

►EpidermisEpidermis — outer layer — outer layer Stratified squamous epitheliumStratified squamous epithelium Often keratinized (hardened by keratin)Often keratinized (hardened by keratin)

►DermisDermis Dense connective tissueDense connective tissue

►Subcutaneous tissueSubcutaneous tissue hypodermishypodermis

Skin StructureSkin Structure

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 corneum

Skin StructureSkin Structure►Subcutaneous tissueSubcutaneous tissue ( (hypodermishypodermis) 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.

Layers of the EpidermisLayers of the Epidermis

►Stratum basaleStratum basale Deepest layer of epidermisDeepest layer of epidermis Cells actively undergoing cell divisionCells actively undergoing cell division New cells are pushed upward to become New cells are pushed upward to become

the more superficial layersthe more superficial layers

►Stratum spinosumStratum spinosum – intermediate layer – intermediate layer►Stratum granulosumStratum granulosum – another layer – another layer

Layers of the EpidermisLayers of the Epidermis

►Stratum lucidumStratum lucidum Formed from dead cells of the deeper layersFormed from dead cells of the deeper layers Occurs only in thick, hairless skin of the Occurs only in thick, hairless skin of the

palms of hands and soles of feetpalms of hands and soles of feet

►Stratum corneumStratum corneum Outermost layer of epidermisOutermost layer of epidermis Scale-like dead cells are filled with keratin Scale-like dead cells are filled with keratin

which is a protective protein preventing which is a protective protein preventing water loss from skinwater loss from skin

KeratinizationKeratinization

► Cells migrate to the epidermis where Cells migrate to the epidermis where eventually they fall off. eventually they fall off.

► As they move upward, keratin is added.As they move upward, keratin is added.► The cells in the epidermis contain a lot of The cells in the epidermis contain a lot of

keratin which resists damage.keratin which resists damage.►Distinct layers of cells are called Distinct layers of cells are called stratastrata..

A cell takes ~ 40 – 56 from creation to sloughing off

MelaninMelanin

►Pigment (melanin) produced by Pigment (melanin) produced by melanocytesmelanocytes

►Melanocytes are mostly in the stratum Melanocytes are mostly in the stratum basalebasale

►Color is yellow to red to brown to blackColor is yellow to red to brown to black►Amount of melanin produced depends Amount of melanin produced depends

upon genetics and exposure to upon genetics and exposure to sunlightsunlight

Melanin continued….Melanin continued….

► 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.

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

► All races have the All races have the same number of same number of melanoctyes! The melanoctyes! The amount of melanin amount of melanin produced is determined produced is determined by genetics.by genetics.

AlbinismAlbinism► A single mutation can cause a deficiency or A single mutation can cause a deficiency or

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

unpigmented eyesunpigmented eyes

DermisDermis►Two layersTwo layers

Papillary layerPapillary layer (upper dermal region) (upper dermal region)► Projections called dermal papillae Projections called dermal papillae

Some contain capillary loops containing bloodSome contain capillary loops containing blood Some pain receptors and touch receptorsSome pain receptors and touch receptors

Reticular layerReticular layer (deepest skin layer) (deepest skin layer)► Blood vesselsBlood vessels► Sweat and oil glandsSweat and oil glands► Deep pressure receptorsDeep pressure receptors

What causes Normal Skin What causes Normal Skin ColorColor

►MelaninMelanin Yellow, brown, or black pigmentsYellow, brown, or black pigments

►CaroteneCarotene Orange-yellow pigment from some vegetablesOrange-yellow pigment from some vegetables

►HemoglobinHemoglobin Red coloring from blood cells in dermal Red coloring from blood cells in dermal

capillariescapillaries Oxygen content determines the extent of red Oxygen content determines the extent of red

coloringcoloring

DermisDermis►Overall dermis structureOverall dermis structure

CollagenCollagen and and elastic fiberselastic fibers located located throughout the dermisthroughout the dermis► Collagen fibersCollagen fibers give skin its toughness give skin its toughness► Elastic fibersElastic fibers give skin elasticity give skin elasticity

Dermal papillaeDermal papillae – extend toward the – extend toward the epidermis and deliver nutrients, remove epidermis and deliver nutrients, remove waste products (sweat = urea and uric waste products (sweat = urea and uric acid) and aid in regulating body acid) and aid in regulating body temperature.temperature.

What causes Normal Skin What causes Normal Skin ColorColor

►MelaninMelanin Yellow, brown, or black pigmentsYellow, brown, or black pigments

►CaroteneCarotene Orange-yellow pigment from some vegetablesOrange-yellow pigment from some vegetables

►HemoglobinHemoglobin Red coloring from blood cells in dermal Red coloring from blood cells in dermal

capillariescapillaries Oxygen content determines the extent of red Oxygen content determines the extent of red

coloringcoloring