Integumentary System By Baasir Umair.pdf

The integumentary system is the largest organ system of the human body, serving as the body's first line of defense against environmental hazards. It includes the skin, hair, nails, glands, and sensory receptors. This system plays a vital role in protection, thermoregulation, sensation, excretion, and vitamin D synthesis. Understanding its structure and function is crucial for comprehending how the body interacts with its surroundings.

Structure of the Integumentary System

The integumentary system comprises two main components:

The Skin (Cutaneous Membrane)

Accessory Structures (Hair, Nails, and Glands)

The Skin

The skin, also called the cutaneous membrane, consists of three primary layers:

1. Epidermis

The epidermis is the outermost layer of the skin, composed of stratified squamous epithelium. It lacks blood vessels and is primarily made of keratinocytes, which produce the protective protein keratin. Other important cells in the epidermis include:

Melanocytes – produce melanin, which protects against UV radiation.

Langerhans cells – involved in immune response.

Merkel cells – associated with sensory neurons for touch perception.

The epidermis has five distinct layers (from deep to superficial):

Stratum basale (germinativum) – contains basal cells responsible for generating new keratinocytes.

Stratum spinosum – provides structural integrity.

Stratum granulosum – where keratinization begins.

Stratum lucidum – found only in thick skin (palms and soles).

Stratum corneum – the outermost layer made of dead keratinized cells.

2. Dermis

The dermis is the thicker, connective tissue layer beneath the epidermis. It consists of collagen and elastic fibers, providing strength and flexibility. The dermis has two layers:

Papillary Layer – composed of loose areolar connective tissue; contains dermal papillae, capillaries, and sensory receptors.

Reticular Layer – made of dense irregular connective tissue; contains sweat glands, hair follicles, and blood vessels.

3. Hypodermis (Subcutaneous Layer)

The hypodermis is a layer of adipose and connective tissue that insulates the body, stores energy, and provides cushioning. It connects the skin to underlying muscles and bones.

Functions of the Integumentary System

The skin performs several essential functions, including:

1. Protection

The skin acts as a physical barrier against microorganisms, dehydration, UV radiation, and harmful chemicals. The acid mantle (low pH) of the skin inhibits bacterial growth.

2. Thermoregulation

The skin helps maintain body temperature through:

Sweating (eccrine and apocrine glands) – evaporative cooling.

Vasodilation – blood vessels widen to release heat.

Vasoconstriction – blood vessels narrow to retain heat.

Goosebumps (arrector pili muscles) – create an insulating layer.

3. Sensation

The skin contains specialized sensory receptors:

Meissner’s corpuscles – detect light touch.

Pacinian corpuscles – sense deep pressure and vibration.

Merkel cells –

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9. Epidermis
•About90%ofepidermalcellsarekeratinocytes(kera-TIN-oˉ-sīts′;keratino-=hornlike;-
cytes=cells),whicharearrangedinfourorfivelayersandproducetheproteinkeratin.
•Keratinocytesproduces:
i.Keratinisatough,fibrousproteinthathelpsprotecttheskinandunderlying
tissuesfromabrasions,heat,microbes,andchemicals.
ii.Keratinocytesalsoproducelamellargranules,whichreleaseawater-repellent
sealantthatdecreaseswaterentryandlossandinhibitstheentryofforeign
materials.
keratinocytes
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10. Epidermis
•About8%oftheepidermalcellsaremelanocytes(MEL-a-noˉ-sīts′;melano-=black),
whichdevelopfromtheectodermofadevelopingembryoandproducethepigment
melanin.
•Theirlong,slenderprojectionsextendbetweenthekeratinocytesandtransfermelanin
granulestothem.
Melanin(MEL-a-nin):
•Itisayellowredorbrown-blackpigmentthatcontributestoskincolorand
absorbsdamagingultraviolet(UV)light.
•Onceinsidekeratinocytes,themelaningranulesclustertoformaprotectiveveil
overthenucleus,onthesidetowardtheskinsurface.Inthisway,theyshieldthe
nuclearDNAfromdamagebyUVlight.
•Althoughtheirmelaningranuleseffectivelyprotectkeratinocytes,melanocytes
themselvesareparticularlysusceptibletodamagebyUVlight
Melanocytes
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17. Stratum Spinosum
Epidermis
Location:
•Thestratumspinosum(spi-NO-sum;spinos-=thornlike)islocatedsuperficialtothestratumbasale.
Structure:
•Composedof8–10layersofkeratinocytes.
•Cellsinthemoresuperficiallayersbecomesomewhatflattened.
CellsCharacteristics:
Keratinocytes:
•Producedbythestemcellsinthebasallayer.
•Containthesameorganellesasthecellsofthestratumbasale.
•Somekeratinocytesretaintheirabilitytodivide.
•Producecoarserbundlesofkeratininintermediatefilamentsthanthebasallayer.
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18. Stratum Spinosum
Epidermis
MicroscopicAppearance:
•Inlivingtissue,keratinocytesareroundedandlarger.
•Duringmicroscopicpreparation,cellsshrinkandpullapart,exceptwheremembranes
joinatdesmosomes,makingthemappearcoveredwiththornlikespines,hencethe
name"spinosum."
DesmosomalProjections:
•Ateachspinelikeprojection,bundlesofkeratinintermediatefilamentsinsertinto
desmosomes,whichtightlyjointhecellstooneanother.
•Thisarrangementprovidesbothstrengthandflexibilitytotheskin.
PresenceofOtherCells:
•Intraepidermalmacrophages:Playaroleinimmunedefense.
•Projectionsofmelanocytes:Contributetopigmentdistribution.
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19. Stratum Granulosum: The Middle Layer of the Epidermis
Epidermis
•Situated at about the middle of the epidermis.
Location:
•Consists of three to five layers of flattened keratinocytes.
Structure:
•Keratinocytes in this layer undergo apoptosis (orderly, genetically programmed
cell death).
•Nuclei and organelles degenerate as cells move farther from the dermal blood
vessels, their source of nutrition.
•Keratin intermediate filaments become more apparent as organelles regress
Degenerated Cell:
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20. Stratum Granulosum: The Middle Layer of the Epidermis
Epidermis
FeaturesofCells:
KeratohyalinGranules:
•Darklystaininggranulesthatassemblekeratinintermediatefilamentsintokeratin.
LamellarGranules:
•Membrane-enclosedgranulesthatfusewiththeplasmamembrane.
•Releasealipid-richsecretionthat:
•Actsasawater-repellentsealant.
•Retardslossandentryofwater.
•Preventsentryofforeignmaterials
.
FunctionalRole:
•Marksthetransitionbetweenthemetabolicallyactivestrataandthedeadcellsofthemore
superficiallayers.
•Asnucleibreakdownduringapoptosis,keratinocyteslosetheabilitytocarryoutvital
metabolicfunctionsanddie
.
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21. Stratum Lucidum: The Clear Layer of the Epidermis
Epidermis
Location:
•Foundonlyinthickskinareassuchas:
Fingertips
Palms
Solesofthefeet
Structure:
•Composedoffourtosixlayersofflattened,clear,deadkeratinocytes.
•Keratinocytesinthislayercontain:
Largeamountsofkeratin
Thickenedplasmamembranes
FunctionalRole:
•Providesanadditionallayerofprotectionandtoughnessinthickskinregions,
wherefrictionandpressurearehigher.
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22. Epidermis
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23. Stratum Corneum: The Outermost Layer of the Epidermis
Epidermis
StructureandComposition:
•Composedof25to30layersofflattened,deadkeratinocytes,butcanrangeupto50ormore
layersinthickskin.
•Thecellsare:
Extremelythinandflat
Enclosedbyaplasmamembrane
Devoidofnucleiandorganelles
Finalproductofthekeratinocytedifferentiationprocess
CellArrangement:
•Cellsoverlaplikescalesonasnake’sskin,providingstructuralintegrity.
•Neighboringlayersformstrongconnections,withplasmamembranesarrangedincomplex,wavy
foldsthatinterlocklikeajigsawpuzzle.
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24. StratumCorneum:TheOutermostLayeroftheEpidermis
Epidermis
Functions:
Protection:
•Shieldsdeeperlayersfrominjuryandmicrobialinvasion.
SheddingandReplacement:
•Cellsinthislayerarecontinuouslyshedandreplacedbycellsfromdeeperstrata.
ResponsetoFriction
CallusFormation:
•Constantexposuretofrictionstimulatesincreasedcellandkeratinproduction,resultinginacallus,
whichisanabnormalthickeningofthestratumcorneum.
Significance
•Providesabarrieragainstenvironmentalthreatswhilemaintainingtheintegrityoftheskinthrough
cellrenewal.
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Dermis
StructureandCompositionoftheDermis
OverviewoftheDermis:
•Thesecond,deeperpartoftheskin,thedermis,iscomposedofdenseirregularconnective
tissuecontainingcollagenandelasticfibers.
•Thiswovennetworkoffibershasgreattensilestrength(resistspullingorstretchingforces).
•Thedermisalsohastheabilitytostretchandrecoileasily.
ThicknessandComponents:
•Thedermisismuchthickerthantheepidermis,andthisthicknessvariesfromregiontoregion
inthebody,reachingitsgreatestthicknessonthepalmsandsoles.
•Itformsaboundarywiththesubcutaneouslayer.Bloodvessels,nerves,glands,andhair
follicles(epithelialinvaginationsoftheepidermis)areembeddedinthedermallayer.
FunctionalImportance:
•Thedermisisessentialtothesurvivaloftheepidermis,andtheseadjacentlayersformmany
importantstructuralandfunctionalrelationships.

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Dermis
TwoPortionsoftheDermis:
•Basedonitstissuestructure,thedermiscanbedividedinto:
•PapillaryPortion:Athin,superficialportion.
•ReticularPortion:Athick,deeperportion.
PracticalUse:
•Leather,whichweuseforbelts,shoes,baseballgloves,andbasketballs,isthedried
andtreateddermisofotheranimals.CellsoftheDermis:
•Thefewcellspresentinthedermispredominantlyincludefibroblasts,withsome
macrophagesandafewadipocytesnearitsboundary.

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Dermis
ThePapillaryRegion:StructureandFunction
OverviewofthePapillaryRegion
•Thepapillaryregionisacrucialcomponentofthedermis,makingupapproximatelyone-fifthof
thethicknessofthetotaldermallayer.
•Thisregionischaracterizedbyitsuniquestructuralandfunctionalproperties,whichplaya
significantroleinskinphysiology.
CompositionofthePapillaryRegion
•Thepapillaryregioniscomposedofthincollagenfibersandfineelasticfibers.
•Thesecomponentsprovidetheskinwithbothstrengthandflexibility,allowingittowithstand
mechanicalstresswhilemaintainingitselasticity.
DermalPapillae:EnhancingSurfaceArea
•Oneofthemostdistinctivefeaturesofthepapillaryregionisthepresenceofdermal
papillae(singular:papilla;derivedfromtheLatinwordpapilla,meaning"nipple").
•Thesearesmall,nipple-shapedstructuresthatprojectintotheundersurfaceoftheepidermis.

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Dermis
FunctionsofDermalPapillae:
•IncreasedSurfaceArea:Thedermalpapillaesignificantlyincreasethesurfaceareaofthepapillary
region,enhancingtheexchangeofnutrients,oxygen,andwasteproductsbetweenthedermisand
theepidermis.
•StructuralSupport:Theyalsostrengthentheconnectionbetweenthedermisandtheepidermis,
preventingthelayersfromseparating
ComponentsWithinDermalPapillae
•Thedermalpapillaearenotjuststructuralelements;theyalsohouseseveralimportantfunctional
components:
1.CapillaryLoops
•Alldermalpapillaecontaincapillaryloops,whicharesmallbloodvessels.These
capillariessupplynutrientsandoxygentotheepidermis,whichlacksitsownblood
supply.
2.TactileReceptors(MeissnerCorpuscles)
•Somedermalpapillaecontainspecializednerveendingsknownastactile
receptorsorMeissnercorpuscles(pronouncedMI-S-ner).

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•Thesereceptorsarehighlysensitivetolighttouchandareparticularlyabundantinareasof
theskinthatrequirehightactilesensitivity,suchasthefingertips,palms,andsoles.
3.FreeNerveEndings
•Otherdermalpapillaecontainfreenerveendings,whichareunspecializeddendritesthatlack
structuralcomplexity.
•Despitetheirsimplestructure,thesenerveendingsarehighlyfunctionalandplayacritical
roleinsensoryperception.
Dermis
SensoryFunctionsofFreeNerveEndings
•Free nerve endings are responsible for initiating signals that give rise to a variety of
sensations, including:
•
Warmth
•
Coolness
•
Pain
•
Tickling
•
Itching.

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ImportanceofthePapillaryRegion
•Thepapillaryregionisnotonlyvitalforstructuralintegritybutalsoforsensoryperception
andthermoregulation.
•Itsrichsupplyofbloodvesselsandnerveendingsmakesitakeyplayerinmaintainingskin
healthandfunction.
•Damagetothisregioncanimpairsensoryabilitiesandcompromisetheskin'sabilitytorepair
itself.
•Byunderstandingthepapillaryregion'sstructureandfunctions,wegaininsightintothe
complexanddynamicnatureoftheskin,whichservesasthebody'sfirstlineofdefense
againstexternalstimuli.
Dermis

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TheReticularRegionoftheDermis
•Thereticularregion(fromreticul-meaningnetlike)formsacrucialpartofthedermis,the
layerofskinbeneaththeepidermis.
•Itisattachedtothesubcutaneouslayerandplaysakeyroleinprovidingstrength,
flexibility,andprotectiontotheskin
.
StructureoftheReticularRegion
•Thereticularregionischaracterizedby:
•Thickcollagenfiberbundles:Thesefiberscreateastrongsupportnetwork
fortheskin.
•Scatteredfibroblasts:Fibroblastsarecellsresponsibleforproducing
collagenandotherextracellularmatrixcomponentsessentialforskin
structure.
•Wanderingcells:Theseincludemacrophages,whicharepartofthe
immunedefensesystemandhelpprotecttheskinfrominfection.
Dermis

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•Adiposecells:Thesefat-storingcellsarefoundinthedeepestpartofthislayerand
helpinsulatethebodyandcushiontissues.
•Coarseelasticfibers:Thesefibersprovidetheskinwithelasticity,allowingitto
stretchandreturntoitsoriginalshape
.
AdditionalComponents
•Bloodvessels:Essentialfornutrientdeliveryandtemperatureregulation.
•Nerves:Providesensoryinputsuchastouch,pressure,andpain.
•Hairfollicles:Thesestructuresproducehairandareanchoredinthereticularregion.
•Sebaceous(oil)glands:Theseglandssecretesebumtokeeptheskinmoisturizedand
protectagainstmicrobialinvasion.
•SudoriferousGland(SweatGland):Theseglandsplayaroleinthermoregulationby
producingsweat.
Dermis

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Dermis
CollagenandElasticFiberArrangement
•Thecollagenfibersinthisregionarearrangedinanetlikepattern,givingthereticularregion
itsname.
•Unliketheirregulararrangementinthepapillaryregion,thereticularregionhasamoreregular
collagenfiberorientation,whichprovidesstructuralstability.
•Thisregularorientationenablestheskintoresiststretchingandmaintainitsintegrityunder
mechanicalstress.
KeyFunctionsoftheReticularRegion
•Thereticularregionprovides:
Strength:Duetothedensecollagenfibernetwork.
Extensibility:Theabilityoftheskintostretchwithouttearing.
Thiscanbeobservedaroundjoints,andduringpregnancyand
obesitywhentheskinstretchestoaccommodatechangesinthe
body'sshape.
.

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Dermis
Elasticity:Theabilityoftheskintoreturntoitsoriginalshapeafterstretching
(e-las-TIS-i-tē).
Elasticfibersarecrucialforallowingtheskintorecoverafter
beingstretched
.
ClinicalRelevance
•Damagetothereticularregion,suchasduringsevereburns,canimpairskinelasticityand
strength,potentiallyrequiringgraftingforhealing.
•Collagendegradationwithagingcontributestowrinklesandsaggingskin.
•Thiscombinationofstructureandfunctionmakesthereticularregionanessential
componentformaintainingskinhealthandresilience.

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Dermis
Clinical Relevance: Tension Lines and Surgery
WhatareTensionLines?
•Tensionlines,alsoknownaslinesofcleavage,arenaturalpatternsintheskinthatindicatethe
predominantdirectionofcollagenfiberswithinthereticularregionofthedermis
.
FormationofTensionLines
•Collagenfibersincertainareasofthebodyaligninspecificdirectionsdueto:
Bonyprojections:Structuralfeaturesoftheskeletonthatinfluenceskin
tension.
Muscleorientation:Thearrangementofunderlyingmuscles.
Jointmovements:Frequentskinstretchingovermovablejoints.
•Thesefactorscreatepredictabletensionpatternsintheskin.

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Dermis
SignificanceinSurgery
•Understandingtensionlinesiscrucialforsurgicalprocedures,particularlyinplastic
andreconstructivesurgery.
AdvantagesofParallelIncisions
•Surgicalincisionsmadeparalleltothecollagenfiberstendtohealwithminimal
scarring,oftenresultinginafinescar.
•Thewoundedgesremainwell-aligned,promotingfasterhealing.
DisadvantagesofPerpendicularIncisions
•Incisionsmadeperpendicularoracrosstherowsofcollagenfibersdisruptthenatural
fiberalignment.
•Thesewoundstendtogapeopen,makingthemmorepronetohealingwithbroad,thick
scars.
ClinicalImplication
•Surgeonsconsidertensionlinesduringprocedurestoachievebettercosmeticoutcomes
andminimizescarring.Knowledgeoftheselinescansignificantlyenhancewound
healingandpatientsatisfaction.

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Dermis
Clinical Relevance: Tension Lines and Surgery
OverviewofEpidermalRidges
•Thesurfacesofthepalms,fingers,soles,andtoesfeatureaseriesofridgesandgrooves.
•Theseridgesmayappearasstraightlines,loops,orwhorls,particularlyevidentonthetipsof
thedigits.
FormationandDevelopmentofEpidermalRidges
•FetalDevelopment:Epidermalridgesformduringthethirdmonthoffetaldevelopmentas
downwardprojectionsoftheepidermisintothedermisbetweenthedermalpapillaeofthe
papillaryregion.
•StructuralBond:Theseridgescreateastrongbondbetweentheepidermisanddermis,
makingtheskinmoreresilientinregionsexposedtohighmechanicalstress.

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Dermis
Clinical Relevance: Tension Lines and Surgery
FunctionsofEpidermalRidges
IncreasedSurfaceArea:
•Enhancesthebondbetweentheepidermisanddermis.
•Increasesgripbyenhancingfrictiononsurfaces.
TactileSensitivity:
•Theridgesincreasethenumberofcorpusclesoftouch,improvingtactilesensitivity.
FormationofFingerprints:
•Sweatporesopenonthetopsofepidermalridges.
•Thecombinationofsweatandridgepatternsformsfingerprints(orfootprints)whentouching
smoothobjects.

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Dermis
Clinical Relevance: Tension Lines and SurgeryGeneticandIndividualUniqueness
•Thepatternofepidermalridgesispartiallygeneticallydeterminedandisuniqueforeach
individual,evenamongidenticaltwins.
•Thepatternremainsunchangedthroughoutlife,exceptforsizeenlargement,makingita
reliablefeatureforidentificationpurposes.

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The Structural Basis of Skin Color
PigmentsContributingtoSkinColor
•Melanin,hemoglobin,andcarotenearethreepigmentsthatimpartawidevarietyofcolorsto
skin.
•Theamountofmelanincausestheskin’scolortovaryfrompaleyellowtoreddish-brownto
black.
TypesofMelanin
•Thedifferencebetweenthetwoformsofmelanin,pheomelanin(fē-oˉ-MEL-a-nin)(yellowto
red)andeumelanin(ū-MEL-a-nin)(browntoblack),issignificant.
•Melaninaccumulatesinpatchescalledfreckles.Frecklestypicallyarereddishorbrownand
tendtobemorevisibleinthesummerthanthewinter.
Age-RelatedSkinChanges
•Asapersonages,age(liver)spotsmaydevelop.
•Theseflatblemisheshavenothingtodowiththeliver.
•Theylooklikefrecklesandrangeincolorfromlightbrowntoblack.Likefreckles,agespots
areaccumulationsofmelanin.

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The Structural Basis of Skin Color
•Agespotsaredarkerthanfrecklesandbuildupovertimeduetoexposuretosunlight.
•Agespotsdonotfadeawayduringthewintermonthsandaremorecommoninadultsover40.
BenignMelanocyteOvergrowth
•Around,flat,orraisedareathatrepresentsabenignlocalizedovergrowthofmelanocytesand
usuallydevelopsinchildhoodoradolescenceiscalledanevus(NE-vus),oramole.
MelaninSynthesisandFunction
•Melanocytessynthesizemelaninfromtheaminoacidtyrosineinthepresenceofanenzyme
calledtyrosinase.Synthesisoccursinanorganellecalledamelanosome(MEL-an-oˉ-soˉm).
EffectsofUVLight
•Exposuretoultraviolet(UV)lightincreasestheenzymaticactivitywithinmelanosomesand
thusincreasesmelaninproduction.
•BoththeamountanddarknessofmelaninincreaseonUVexposure,whichgivestheskina
tannedappearanceandhelpsprotectthebodyagainstfurtherUVradiation.

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The Structural Basis of Skin Color
ProtectiveRoleofMelanin
•MelaninabsorbsUVradiation,preventsdamagetoDNAinepidermalcells,andneutralizes
freeradicalsthatformintheskinfollowingdamagebyUVradiation.
•Thus,withinlimits,melaninservesaprotectivefunction.InresponsetoDNAdamage,
melaninproductionincreases.
VitaminDSynthesisandSkinCancerRisk
•Asyouwillseelater,exposingtheskintoasmallamountofUVlightisactuallynecessaryfor
theskintobegintheprocessofvitaminDsynthesis.
•However,repeatedlyexposingtheskintoalargeamountofUVlightmaycauseskincancer.
•Atanislostwhenthemelanin-containingkeratinocytesareshedfromthestratumcorneum.

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Skin Color Variations
Dark-SkinnedIndividuals
•Dark-skinnedindividualshavelargeamountsofmelaninintheepidermis,sotheirskincolor
rangesfromyellowtoreddish-browntoblack.
Light-SkinnedIndividuals
•Light-skinnedindividualshavelittlemelaninintheepidermis.
•Thus,theepidermisappearstranslucent,andskincolorrangesfrompinktoreddepending
ontheoxygencontentofthebloodmovingthroughcapillariesinthedermis.
•Theredcolorisduetohemoglobin(hē-moˉ-GLO-bin),theoxygen-carryingpigmentinred
bloodcells.
CaroteneandItsRole
•Carotene(KAR-oˉ-tēn;carot=carrot)isayellow-orangepigmentthatgiveseggyolksand
carrotstheircolor.
•ThisprecursorofvitaminA,whichisusedtosynthesizepigmentsneededforvision,is
storedinthestratumcorneumandfattyareasofthedermisandsubcutaneouslayerin
responsetoexcessivedietaryintake.

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Skin Color Variations
EffectsofExcessiveCaroteneIntake
•Infact,somuchcarotenemaybedepositedintheskinaftereatinglargeamountsof
carotene-richfoodsthattheskinactuallyturnsorange,whichisespeciallyapparentinlight-
skinnedindividuals.
•Decreasingcaroteneintakeeliminatestheproblem.
DistributionofMelanocytes
•Melanocytes,themelanin-producingcells,aremostplentifulintheepidermisofthepenis,
nipplesofthebreasts,areajustaroundthenipples(areolae),face,andlimbs.
•Theyarealsopresentinmucousmembranes.
•Becausethenumberofmelanocytesisaboutthesameinallpeople,differencesinskincolor
areduemainlytotheamountofpigmentthemelanocytesproduceandtransferto
keratinocytes.
GeneticPredisposition
•Insomepeoplewhoaregeneticallypredisposed,themelaninproductionandtransfer
processesmayvary,leadingtodifferentskintonesandsusceptibilitytopigmentation
changes.

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Albinism and Vitiligo
Albinism
•Albinism(AL-bin-izm;albin-=white)istheinheritedinabilityofanindividualtoproduce
melanin.
CharacteristicsofAlbinism
•Mostalbinos(al-BI-noˉs),peopleaffectedbyalbinism,havemelanocytesthatareunableto
synthesizetyrosinase.Melaninismissingfromtheirhair,eyes,andskin.
ConsequencesofAlbinism
•Thisresultsinproblemswithvisionandatendencyoftheskintoburneasilyon
overexposuretosunlight.
Vitiligo
•Inanothercondition,calledvitiligo(vit-i-LI-goˉ),thepartialorcompletelossofmelanocytes
frompatchesofskinproducesirregularwhitespots.
CauseofVitiligo
The loss of melanocytes is related to an immune system malfunction in which antibodies attack
the melanocytes
.

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Albinism Vitiligo

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57. HairBulb
•Thebaseofeachhairfollicleanditssurroundingdermalrootsheathformsanonion-shapedstructure
calledthehairbulb.
•Thehairbulbcontains:
•PapillaoftheHair:Anipple-shapedindentationthathousesareolarconnectivetissueandblood
vessels,whichnourishthegrowinghairfollicle.
•HairMatrix:Agerminallayerofcellsresponsibleforhairgrowthandregeneration.
Anatomy of Hair
Function of the Hair Matrix
•Thehairmatrixcellsoriginatefromthestratumbasale,thesiteofcelldivision.
•Thesecells:
•Facilitatethegrowthofexistinghairs.
•Producenewhairstoreplaceoldhairswhentheyareshed.
•Regeneratehairswithinthesamefollicle.
•Giverisetothecellsoftheinternalrootsheath.

58. Anatomy of Hair
HairRemovalMethods
Depilatory
•
Adepilatory(de-PIL-a-toˉ-rē)isasubstancethatremoveshair.
•
Itworksbydissolvingtheproteininthehairshaft,turningitintoagelatinousmassthatcanbe
wipedaway.
•
Sincethehairrootremainsunaffected,regrowthoccurs.
•
GenericName:Chemicaldepilatoriesoftencontaincalciumthioglycolateorpotassium
thioglycolateasactiveingredients.
Electrolysis
•
Inelectrolysis,anelectriccurrentisusedtodestroythehairmatrix.
•
Thispreventsthehairfromregrowing.
LaserTreatments
•
Lasertreatmentsareanothermethodusedtoremovehair.

59. Sebaceous (Oil) Glands and ArrectorPili
Sebaceous(Oil)Glands
:
Theseglandsareassociatedwithhairs(discussedshortly).SmoothMuscle(ArrectorPili):
•
Definition:Thearrectorpili(a-REK-torPI-lī;arrect-=toraise)isabundleofsmooth
musclecellsassociatedwithhairs.
•
Location:Extendsfromthesuperficialdermisoftheskintothedermalrootsheath
aroundthesideofthehairfollicle.

Function:

NormalPosition:Hairemergesatalessthan90-degreeangletothesurfaceofthe
skin.

ResponsetoStress:Underphysiologicaloremotionalstress(e.g.,coldorfright),
autonomicnerveendingsstimulatethearrectorpilimusclestocontract.

Result:Thiscontractionpullsthehairshaftperpendiculartotheskinsurface,
causing"goosebumps"or"gooseflesh"astheskinaroundtheshaftformsslight
elevations.

60. Sebaceous (Oil) Glands and ArrectorPili
Hair Follicle and Sensory Function
Hair Root Plexus:
Structure: Surrounding each hair follicle are dendrites of neurons that form a hair root plexus
(PLEK-sus).
Function:
Sensitivity: The hair root plexus is sensitive to touch.
Response: Generates nerve impulses if the hair shafts are moved.

61. Sebaceous (Oil) Glands and Smooth Muscle
Sebaceous Glands (Oil Glands)
Structure and Location
•
Type:Simple,branchedacinar(rounded)glands
•
Connection:Mostlyconnectedtohairfollicles
•
LocationofSecretoryPortion:Liesinthedermisandusuallyopensintotheneckof
ahairfollicle
•
DirectlyOpeningontoSkinSurface:
•
Foundinspecificareassuchas:
Lips
Glans penis
Labia minora
Tarsal glands of the eyelids
•
Absentin:
Palms
Soles

62. Sebaceous (Oil) Glands and Smooth Muscle
SizeVariation:
•
Smallinmostareasofthetrunkandlimbs
•
Largeinthebreasts,face,neck,andsuperiorchest
Secretion:Sebum
Composition:
•
Mixtureoftriglycerides,cholesterol,proteins,andinorganicsalts
Functions:
•
Coatsthesurfaceofhairs,preventingthemfromdryingand
becomingbrittle
•
Preventsexcessiveevaporationofwaterfromtheskin
•
Keepstheskinsoftandpliable
•
Inhibitsthegrowthofsomebacteria(butnotall
)

63. Sweat Glands
Overview:
•There are three million to four million sudoriferous (sweat) glands in the body. These glands
release sweat into hair follicles or onto the skin surface through pores.
Types of Sweat Glands
•Sweat glands are categorized into three main types based on their structure and secretion:
1.Eccrine Sweat Glands
2.Apocrine Sweat Glands
3.Ceruminous Glands (a specialized type of apocrine gland)

64. Sweat Glands
EccrineSweatGlands
StructureandDistribution
•Simple,coiledtubularglands
•Morecommonthanapocrinesweatglands
•Distributedthroughoutmostregionsofthebody,especiallyontheforehead,palms,andsoles
•Absentincertainareassuchasthelips,nailbeds,glanspenis,glansclitoris,labiaminora,and
eardrums
•Secretoryportionislocatedinthedeepdermisoruppersubcutaneouslayer
•Excretoryductopensatthesurfaceoftheepidermisasapore
CompositionofSweat
•Primarilywater
•Smallamountsofions(Na⁺andCl⁻),urea,uricacid,ammonia,aminoacids,glucose,and
lacticacid

65. Sweat Glands
Functions
•Thermoregulation:
Regulatesbodytemperaturethroughsweatevaporation
Processiscalledthermoregulatorysweating
Beginsontheforeheadandscalp,thenspreadstotherestofthebody,
withpalmsandsolessweatinglast
•Insensibleperspiration:
Sweatthatevaporatesbeforebeingperceivedasmoisture
•Sensibleperspiration:
Sweatthatappearsasmoistureontheskin
•WasteElimination:
Helpsremoveurea,uricacid,andammonia(thoughkidneysplaya
largerrole)
•EmotionalSweating:
Responsetostress,fear,orembarrassment
Alsocalledcoldsweat
Beginsonpalms,soles,andaxillaebeforespreading

66. Sweat Glands
ApocrineSweatGlands
StructureandDistribution
•Simple,coiledtubularglandswithlargerductsandlumensthaneccrineglands
•Foundmainlyintheaxilla(armpits),groin,areolae(nipples),andbeardedregionsofadult
males
•Secretoryportionislocatedinthelowerdermisoruppersubcutaneouslayer
•Excretoryductopensintohairfollicles.
CompositionofSweat
•Containsthesamecomponentsaseccrinesweatpluslipidsandproteins
•Appearsmilkyoryellowishincolor
•Initiallyodorless,butdevelopsamuskyodor(bodyodor)whenmetabolizedbyskinbacteria

67. Sweat Glands
Functions
•Emotional Sweating:
Activeduringstress-relatedsweatingalongwitheccrineglands
•Sexual Activity
:
Secretessweatduringsexualactivities
•No Role in Thermoregulation:
Unlikeeccrinesweatglands,apocrineglandsarenotinvolvedin
regulatingbodytemperature
•Activation
Eccrinesweatglandsstartfunctioningsoonafterbirth
Apocrinesweatglandsbecomeactiveonlyatpuberty

68. Sweat Glands
CeruminousGlands(ASpecializedApocrineSweatGland)
StructureandLocation
•Modifiedapocrinesweatglandslocatedintheexternalear
•Secretoryportionslieinthesubcutaneouslayer,deeptosebaceousglands
•Excretoryductsopeneither:
Directlyontothesurfaceoftheexternalauditorycanal(earcanal)
Intoductsofsebaceousglands

69. Sweat Glands
SecretionandFunction
•Producesawaxylubricatingsecretion
•Formscerumen(earwax),ayellowishmaterial
•Cerumen,alongwithhairsintheearcanal,servesasaprotectivebarrierby:
Trapping foreign bodies and insects
Waterproofing the ear canal
Preventing bacterial and fungal infections
CombinedSecretion
•Thesecretionofceruminousandsebaceousglandstogetherformsearwax,whichprotectsand
maintainsearhealth.

70. Sweat Glands
SecretionandFunction
•Producesawaxylubricatingsecretion
•Formscerumen(earwax),ayellowishmaterial
•Cerumen,alongwithhairsintheearcanal,servesasaprotectivebarrierby:
Trapping foreign bodies and insects
Waterproofing the ear canal
Preventing bacterial and fungal infections
CombinedSecretion
•Thesecretionofceruminousandsebaceousglandstogetherformsearwax,whichprotectsand
maintainsearhealth.

71. Sebaceous (Oil) Glands and Smooth Muscle
SizeVariation:
•
Smallinmostareasofthetrunkandlimbs
•
Largeinthebreasts,face,neck,andsuperiorchest
Secretion:Sebum
Composition:
•
Mixtureoftriglycerides,cholesterol,proteins,andinorganicsalts
Functions:
•
Coatsthesurfaceofhairs,preventingthemfromdryingand
becomingbrittle
•
Preventsexcessiveevaporationofwaterfromtheskin
•
Keepstheskinsoftandpliable
•
Inhibitsthegrowthofsomebacteria(butnotall
)

72. Nail Anatomy

73. Nail Anatomy
StructureofNails
Composition:
•Madeoftightlypacked,hard,dead,keratinizedepidermalcells
•Formsaclear,solidcoveringoverthedorsalsurfaceofthedistalportionsof
digits
MainPartsoftheNail:
1.NailBody(Plate)
•Visibleportionofthenail
•Comparabletothestratumcorneum,butcontainsharderkeratin
•Notshedlikenormalepidermalcells
•Appearspinkduetobloodflowinthecapillariesoftheunderlyingdermis
2.FreeEdge
•Extendspastthedistalendofthedigit
•Appearswhiteduetolackofunderlyingcapillaries

74. Nail Anatomy
3.NailRoot
•Buriedinafoldofskin
4.Lunula
•Whitish,crescent-shapedareaattheproximalendofthenailbody
•Appearswhitishbecausetheunderlyingvasculartissueisobscuredby
thickenedepithelium
5.Hyponychium
•Thickenedregionofstratumcorneumbeneaththefreeedge
•Securesthenail
tothefingertip
6.Nail Bed
•Skinbelowthenailplate
•Extendsfromthelunulatothehyponychium
•Lacksastratumgranulosum
6.Eponychium (Cuticle)
•Narrowbandofepidermisadheringtothelateralborderofthenailwall
•Occupiestheproximalborderofthenail
•Consistsofstratumcorneum

75. Nail Anatomy
7. Hangnail
•
smalltornpieceofskinatthesideorbaseofanail,causedbydrynessofthe
eponychium
Nail Growth
Nail Matrix:
•Locatedproximaltothenailroot
•Superficialmatrixcellsdividemitoticallytoformnewnailcells
•Growthratedependson:
Age
Health
Nutritionalstatus
Season,timeofday,andenvironmentaltemperature
•Averagegrowthrate:~1mmperweek
•Fingernailsgrowfasterthantoenails
•Longerdigitshavefaster-growingnails

76. Nail Anatomy
Functions of Nails
•Protect the distal end of digits
•Enhance touch perception and manipulation by providing
support and counterpressureto fingers
•Assist in grasping and handling small objects
•Aid in scratching and grooming

77. References
1.Tortora,G.J.,&Derrickson,B.( 2021( .PrinciplesofAnatomyand
Physiology)16 thed.).Wiley.
2.Marieb,E.N.,&Hoehn,K.( 2019(.HumanAnatomy&Physiology)11 th
ed.).Pearson.
3.Martini,F.H.,Nath,J.L.,&Bartholomew,E.F.( 2018(.Fundamentalsof
Anatomy&Physiology)11 thed.).Pearson.
4.Saladin,K.S.( 2020(.Anatomy&Physiology :TheUnityofFormand
Function)9 thed.).McGrawHill.