SkinSkin andand skinskin appendagesappendages

LIU ying HISTOLOGY AND EMBRYOLOGY TheThe skinskin isis thethe largestlargest organorgan ofof thethe body.body. AppendagesAppendages include:include: FunctionsFunctions include:include: 1.1. ProtectiveProtective 2.Sensory2.Sensory 3.Exocrine3.Exocrine epidermisepidermis | ItIt isis thethe outerouter avascularavascular epithelialepithelial layer.layer. | ItIt consistsconsists ofof aa keratinizedkeratinized stratifiedstratified squamoussquamous epithelium.epithelium. | ItIt consistsconsists ofof 55 layerslayers fromfrom dermisdermis outward.outward. | ItIt isis composedcomposed ofof keratinocyteskeratinocytes andand nonkeratinocytesnonkeratinocytes.. 11.. stratum basale

| AA layerlayer ofof columnarcolumnar oror cuboidalcuboidal cellscells

| PlasmaPlasma isis basophilicbasophilic（（lysosomelysosome）；）； keratinkeratin filamentfilament

| TheseThese cellscells areare connectedconnected toto oneone anotheranother byby desmosomesdesmosomes,, toto thethe basalbasal laminalamina byby hemidesmosomeshemidesmosomes..

| TheyThey areare stemstem cellscells；；constantconstant renewalrenewal ofof epithelialepithelial cell.cell.

22.. stratumstratum spinosumspinosum | ItIt isis typicallytypically severalseveral cellscells thickthick | ItIt isis polygonalpolygonal cells,cells, cuboidalcuboidal oror slightlyslightly flattened,flattened, centralcentral nucleus,nucleus, numerousnumerous ribosomeribosome | CytoplasmCytoplasm isis palepale basophilic,basophilic, areare filledfilled withwith bundlesbundles ofof keratinkeratin filamentsfilaments ((tonofilamenttonofilament））.. | spinesspines ofof adjacentadjacent cellscells attachattach eacheach otherother byby dosmosomedosmosome..

Figure 6 Stratum spinosum of the skin from the sole of the foot (thick skin) showing the spiny projections that strongly bind the cells of this layer together to resist abrasion. Pararosaniline- toluidine blue stain. Medium magnification. Electron micrographs of the stratum spinosum. A: A cell of the stratum spinosum with melanin granules and the cytoplasm full of tonofilaments. The arrows show the spines with their desmosomes. x8400. B and C: The desmosomes from A, in greater detail. Note that a dense substance appears between the cell membranes and that bundles of cytoplasmic tonofilaments (F) insert themselves on the desmosomes. 33.. stratumstratum granulosumgranulosum | usuallyusually 33～～55 layerslayers thickthick | CellsCells areare flattendNucleiflattendNuclei andand organellsorganells havehave degenerateddegenerated | cytoplasmcytoplasm isis filledfilled withwith tonofilamentstonofilaments.. | isis filledfilled withwith coarsecoarse basophilicbasophilic granulesgranules ((keratohyalinkeratohyalin granules,granules, nono membrane)membrane)------intracellularintracellular cementcement | MembraneMembrane coatedcoated lamellarlamellar granulesgranules ------intercellularintercellular cementcement

Lamellar disk are formed by lipid bilayer 44.. stratumstratum lucilumlucilum | CharacteristicCharacteristic ofof onlyonly thickthick skin,skin, thinthin layerlayer | CellsCells areare extremelyextremely flat.flat. | cytoplasmcytoplasm isis eosinophiliceosinophilic.. | OrganellsOrganells andand nucleinuclei areare nono longerlonger evident.evident. | DesmosomesDesmosomes areare stillstill evidentevident betweenbetween adjacentadjacent cells.cells. 55.. stratumstratum corneumcorneum | 15~2015~20 layerslayers | CellsCells areare flat,flat, nonnucleatednonnucleated.. | PlasmaPlasma isis eosinophiliceosinophilic,, filledfilled withwith keratin.keratin. | TonofilamentsTonofilaments areare packedpacked togethertogether inin aa matrixmatrix contributedcontributed byby keratohyalinkeratohyalin granules.granules. | PlasmaPlasma membranesmembranes areare coatedcoated withwith anan extraextra--cellularcellular lipidlipid layer.layer. | HornyHorny cellscells areare continuouslycontinuously shedshed atat thethe surfacesurface ofof thethe stratumstratum corneumcorneum.. CONCLUSION TheThe changeschanges ofof thethe keratinizedkeratinized cellscells fromfrom basalbasal layerlayer toto cornifiedcornified layerlayer showshow thethe processprocess ofof thethe keratinizationkeratinization:: ①①Morphology:Morphology: ColumnerColumner→→ polygonalpolygonal→→ spindlespindle→→ flattened;flattened; basophilicbasophilic→→acidophilicacidophilic ②② Nuclei./Nuclei./ Organelle:Organelle: ++→→----;; ③③ LamellarLamellar G:G: ---- →→ ++++ →→ ---- ((exocytosisexocytosis)) ④④ plasmaplasma membrane:membrane: 66--10nm10nm →→ 1515--20nm;20nm; ⑤⑤ keratin:keratin: ---- →→ ++++ →→ ++++++++ ⑥⑥ Filaments:Filaments: lessless→→many;many; scatteredscattered→→bundle;bundle; ⑦⑦ DesmosomesDesmosomes:: ++ →→ ----;; 1.1. melanocytemelanocyte | FoundFound nearnear thethe basebase ofof thethe epidermisepidermis |DerivedDerived fromfrom neuralneural crestcrest cellcell |LMLM darkdark nucleinuclei，，lightlight cytoplasmcytoplasm dendriticdendritic processesprocesses extendextend intointo thethe stratumstratum spinosumspinosum.. | EMEM containcontain numerousnumerous mitochondria,mitochondria, lysosomelysosome、、 RERRER、、GolgiGolgi complexcomplex | FUNCTIONSFUNCTIONS MelanocytesMelanocytes synthesizesynthesize melaninmelanin andand distributedistribute itit toto thethe keratinocyteskeratinocytes toto protectprotect themthem fromfrom thethe mutagenicmutagenic effecteffect ofof UVUV radiation.radiation. Fig.5 Diagram of a melanocyte. Its processes extend into the interstices between keratinocytes. The melanin granules are synthesized in the melanocyte, migrate to its processes, and are transferred into the cytoplasm of keratinocytes.

Fig.8 Diagram of a melanocyte. Its processes extend into the interstices between keratinocytes. The melanin granules are synthesized in the melanocyte, migrate to its processes, and are transferred into the cytoplasm of keratinocytes. P

P P M

Fig.9 melanocyte (M melanin granules P processes K kerotinocytes BL basal lamina D dermis) 2.2. LangerhansLangerhans cellcell | FoundFound mainlymainly inin thethe ST.ST. spinosumspinosum.. | DerivedDerived fromfrom stemstem cellscells inin thethe bonebone marrowmarrow | LMLM StarStar--shapedshaped，，lightlight cytoplasmcytoplasm nono desmosomes | FUNCTIONFUNCTION antigenantigen--presentingpresenting cells,cells, partpart ofof thethe mononuclearmononuclear phagocytoticphagocytotic systemsystem (MPS).(MPS). Bind,process.presentBind,process.present

Fig.10 Langerhans cells (ATPase stain) 3.3. MerkleMerkle’’ss cellcell

| foundfound inin thethe stratumstratum basalebasale..

| ShortShort processes,processes, smallsmall densedense granules,granules, lobed nuclear, desmosomes

| InIn combinationcombination withwith sensorysensory neuronneuron endingsendings inin thethe basalbasal lamina,lamina, MerkelMerkel cellscells formform aa mechanoreceptormechanoreceptor,, maymay bebe related to the diffuse neuro-endocrine system. Fig.12 Merkel’s cell与神经末梢超微结构模式图 （N 梅克尔细胞核,P 胞质突, D 桥粒,CY 糖原,GO 高尔基复合体 G 分泌颗粒,BM 基膜,A 轴突,NP 神经板） Fig.13 Merkel’s cell DermisDermis papillarypapillary layerlayer | TheThe projectionsprojections ofof thethe dermisdermis intointo thethe epidermisepidermis areare calledcalled dermaldermal papillae.papillae. | isis comprisedcomprised ofof aa LCT,LCT, moremore cells,cells, moremore cap.cap. | TactileTactile corpusclecorpuscle | Function: strengthening connection; touch feeling; nourishment 2.2. reticularreticular layerlayer | lieslies deepdeep toto thethe papillarypapillary layerlayer | isis typicallytypically thickerthicker andand fewerfewer cellscells | ItIt hashas largerlarger diameterdiameter typetype II collagencollagen andand elasticelastic fibers.fibers. | Sweat glands, Sebaceous glands, Hair folliciles | lamellated corpuscles Fig.14 papillary layer Fig.11. Photomicrograph of thin skin stained for fibers of the elastic system. Note the gradual decrease in the diameter of fibers as they approach the epidermis. The thick fibers are elastic fibers. Those with an intermediate diameter are elaunin fibers. The very thin superficial fibers are oxytalan fibers formed by microfibrils that insert into the basement membrane. Weigert stain. Medium magnification. HypodermisHypodermis | BeneathBeneath thethe dermisdermis lieslies hypodermis.hypodermis. | comprisedcomprised ofof adiposeadipose andand LCT.LCT. | ItIt isis thethe principalprincipal areaarea ofof fatfat storage,storage, providingproviding bothboth energyenergy reservesreserves andand insulationinsulation 1. hairs

| Hair shaft

| hair root

| Hair follicle hair bulb Hair papilla Hair matrix

periferalepcells. root sheath(internal, root sheath external) CT. root sheath | hairhair bulbbulb ：： TheThe bulbbulb isis aa proliferativeproliferative zonezone formedformed byby thethe epithelialepithelial matrixmatrix cellscells andand dermaldermal papilla.papilla. | dermaldermal papillapapilla ：：AtAt thethe basebase ofof thethe hairhair bulb,bulb, capillarycapillary networknetwork | matrixmatrix cellscells：：covercover thethe dermaldermal papillapapilla andand givegive riserise toto bothboth thethe hairhair andand rootroot sheathsheath rootroot sheathsheath | epep.. rootroot sheathsheath TheThe outermostoutermost cellscells ofof dermaldermal papillapapilla givegive riserise toto thethe internalinternal andand externalexternal rootroot sheath.sheath. | connectiveconnective tissuetissue sheathsheath dermisdermis surroundingsurrounding thethe folliclefollicle Fig.16 Relationships between the skin, hair follicle, arrector pili muscle, and sebaceous and sweat glands. The arrector pili muscle originates in the connective tissue sheath of the hair follicle and inserts into the papillary layer of the dermis, where it ends. Fig.17 The follicle has a bulbous terminal expansion with a dermal papilla. The papilla contains capillaries and is covered by cells that form the hair root and develop into the hair shaft. The central cells (A) form the medulla of the hair. The cells that produce the cortex of the hair are located laterally (B). Cells forming the hair cuticle originate in the next layer (C). The peripheral epithelial cells develop into ep. root sheaths. The AB external root sheath is continuous C with the epidermis, whereas the cells of the internal root sheath disappear at the level of the openings of the sebaceous gland dt Fig.18 hair root、hair follicle、hair bulb、dermal papilla cuticlecuticle arrectorarrector pilipili musclesmuscles : bundlesbundles ofof smoothsmooth musclemuscle cells.cells. disposeddisposed inin anan obliqueoblique direction.direction.

Function:Function: 1.1. contractioncontraction resultsresults inin thethe erectionerection ofof thethe hairhair shaftshaft toto aa moremore uprightupright position.position. 2.Contraction2.Contraction causescauses aa depressiondepression inin thethe skinskin wherewhere thethe musclesmuscles attachattach toto thethe dermis.dermis. ThisThis contractioncontraction producesproduces thethe "gooseflesh""gooseflesh" ofof commoncommon parlance.parlance. Fig.19 sebaceous gland and hair follicle 22.. SebaceousSebaceous glandsglands | secretorysecretory portion:portion: 1.a1.a basalbasal layerlayer ofof undifferentiatedundifferentiated flattenedflattened epithelialepithelial cellscells at periphery 2.rounded2.rounded cellscells containingcontaining increasingincreasing amountsamounts ofof fatfat dropletsdroplets inin center,center, TheirTheir nucleinuclei graduallygradually shrink,shrink, | ductduct：：shortshort，，openopen | Function: releaserelease sebum,sebum, soften skin and kill bacteria. Fig.20 Sebaceous gland. This is a holocrine gland, because its product is secreted with the remnants of a dead cell. Stem cells (arrows) in the base of the gland proliferate to replace the lost cells. Collagen fibers are stained in red. PSP stain. Medium magnification. 3.3. SweatSweat glandsglands areare simple,simple, coiledcoiled tubulartubular glands.glands.

| secretorysecretory portionportion ：：pyramidalpyramidal cellscells ，，palepale stainstain；；surroundedsurrounded byby myoepithelialmyoepithelial cellscells

| ductduct：：twotwo layerslayers ofof palepale basophilicbasophilic cuboidalcuboidal cellscells

| Function:Function: 1.the1.the excretionexcretion ofof nitrogenousnitrogenous waste.waste. 2.2.thermoregulationthermoregulation byby meansmeans evaporativeevaporative cooling.cooling. Figure21. Low-magnification photomicrograph of a section of sweat gland. This is a simple coiled tubular gland. H&E stain. Figure 22. Section of sweat gland. Note the duct lined by stratified cuboidal epithelium. The myoepithelial cells, whose contraction helps to discharge the glandular secretion, surround the secretory portion. H&E stain. Medium magnification.

SummarySummary

| Master the general structure of skin. | Know sebaceous glands, sweat glands and hair generally.